WO2016087439A1 - One-dimensional planar photonic crystals including fluoropolymer compositions and corresponding fabrication methods - Google Patents

One-dimensional planar photonic crystals including fluoropolymer compositions and corresponding fabrication methods Download PDF

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WO2016087439A1
WO2016087439A1 PCT/EP2015/078202 EP2015078202W WO2016087439A1 WO 2016087439 A1 WO2016087439 A1 WO 2016087439A1 EP 2015078202 W EP2015078202 W EP 2015078202W WO 2016087439 A1 WO2016087439 A1 WO 2016087439A1
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group
rpm
photonic crystals
fluoropolymer
dielectric
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PCT/EP2015/078202
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French (fr)
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Stefano Vincenzo RADICE
Padmanabhan Srinivasan
Davide COMORETTO
Serena GAZZO
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Solvay Specialty Polymers Italy S.P.A.
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Publication of WO2016087439A1 publication Critical patent/WO2016087439A1/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/20—Filters
    • G02B5/28—Interference filters
    • G02B5/281—Interference filters designed for the infrared light
    • G02B5/282—Interference filters designed for the infrared light reflecting for infrared and transparent for visible light, e.g. heat reflectors, laser protection
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
    • G02B1/002—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of materials engineered to provide properties not available in nature, e.g. metamaterials
    • G02B1/005—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of materials engineered to provide properties not available in nature, e.g. metamaterials made of photonic crystals or photonic band gap materials
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/08—Mirrors
    • G02B5/0816—Multilayer mirrors, i.e. having two or more reflecting layers
    • G02B5/0825—Multilayer mirrors, i.e. having two or more reflecting layers the reflecting layers comprising dielectric materials only
    • G02B5/0841—Multilayer mirrors, i.e. having two or more reflecting layers the reflecting layers comprising dielectric materials only comprising organic materials, e.g. polymers
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/1225—Basic optical elements, e.g. light-guiding paths comprising photonic band-gap structures or photonic lattices

Definitions

  • the present invention relates to one-dimensional planar photonic crystals. More specifically, the present invention relates to one-dimensional photonic crystals including a fluoropolymer composition.
  • One-dimensional photonic crystals owing to their potential technological applications, have a significant interest in the fields of optics and photovoltaics.
  • One-dimensional planar photonic crystals have been investigated for use in a variety of applications including, but not limited to, optical filters, waveguides, very low threshold lasers, and photovoltaic devices (e.g., crystalline silicon photovoltaic cells, polymeric bulk heterojunctions, fluorescent concentrators, dye-sensitized solar cells).
  • One-dimensional photonic crystals have a periodic dielectric layer structure.
  • the photonic crystals are constructed by sequentially forming dielectric layers with distinct compositions to form the periodic structure of the crystal.
  • the number of layers required to achieve a desirable reflectivity can significantly affect manufacturing time and costs. For example, an increased number of layers can lead to an increased probability of manufacturing errors or increased manufacturing costs. Furthermore, an increased number of layers can also lead to an increased probability of performance failure.
  • the invention in a first aspect, relates to a one-dimensional photonic crystal including a first dielectric layer having a refractive index 3 ⁇ 4 and comprising a fluoropolymer.
  • the one-dimensional photonic crystal further includes a second dielectric layer having a refractive index n 2 ⁇ 3 ⁇ 4 and comprising a second polymer composition.
  • the fluoropolymer is a polymer including an alicyclic structure in the polymer main chain or an elastomer comprising a fluoropolyether chain.
  • the one-dimensional photonic crystal has a thermal shielding of between about 5% to about 75% when irradiated with light having a power of about 150 W, a colour temperature of about 3500 K and a spot size of about 4.75 mm, relative to a glass substrate having substantially the same dimensions.
  • the one-dimensional photonic crystal includes a plurality of first dielectric layers and a plurality of second dielectric layers, with the first dielectric layers and second dielectric layers are alternately stacked and where the one-dimensional photonic crystals includes from 5 to 100 first dielectric layers and from about 5 to 100 second dielectric layers.
  • the one-dimensional photonic crystal has a band gap from about 300 nm to about 3000 nm.
  • the first dielectric layer has a thickness of from about 50 nm to about 5 ⁇ .
  • the photonic crystal has at least 10 repeat units, where 10 sequential repeat units have a reflectivity of at least 50% for a wavelength from about 300 nm to about 3000 nm, and where each of the 10 sequential repeat units comprises the first dielectric layer and the second dielectric layer in a stacked configuration.
  • 3 ⁇ 4 is from about 1.1 to about 1.6.
  • the fluoropolymer is a polymer having an alicyclic structure in the polymer main chain and including recurring units represented by:
  • Ri , R 2 , R 3 and R 4 are independently selected from the group consisting of -F, a Ci-C 6 fluoroalkyl, optionally comprising one or more oxygen atoms, a Ci-C 6 fluoroalkoxy, optionally comprising one or more oxygen atoms;
  • R5 and R6, equal to or different from each other, are independently selected from the group consisting of -F, a Ci-C 6 fluoroalkyl, optionally comprising one or more oxygen atoms, a Ci-C 6 fluoroalkoxy, optionally comprising one or more oxygen atoms; or
  • the fluoropolymer is an elastomer comprising a fluoropoly ether chain, obtained by the UV-curing of compositions comprising: at least one functional fluoropolyether compound comprising a fluoropolyoxyalkylene chain (R f ) and having at least two unsaturated moieties; and at least one photoinitiator.
  • the functional fiuoropolyether compound is selected from the group consisting of compounds of formula (IV):
  • R f represents a fluoropolyoxyalkylene chain comprising recurring units having general formula: -(CF 2 ) k -CFZ-0-, wherein k is an integer of from 0 to 3 and Z is a fluorine atom or a C1-C 5 perfiuoroalkyl group, optionally comprising one or more oxygen atom;
  • J and J' are independently a bond or a divalent bridging group
  • Ti and T 2 are selected from the group consisting of:
  • R H is H or a Ci-C 6 alkyl group
  • R A is selected from the group consisting of:
  • R B is a divalent group selected from the group consisting of C1-C10 aliphatic group, C 5 -C14 cyclo aliphatic group; C 6 -Ci4 aromatic or alkylaromatic group.
  • the second dielectric layer comprises poly(methyl methacrylate), polycarbonate, polystyrene, cellulose acetate, poly(vinyl carbazole), or any combination thereof.
  • the photonic crystal can be made by a method including forming a first layer on a substrate, the forming comprising spin- coating a first precursor solution onto the substrate, wherein the first precursor solution comprises a solvent and from about 0.1 % weight by volume to about 50% weight by volume of a fluoropolymer and wherein the substrate is spun at a speed of about 1000 rpm to about 20000 rpm. In some embodiments of the method, the substrate is spun at a speed from about 1000 rpm to about 15000 rpm.
  • FIG. 1 is a schematic depiction of a one-dimensional photonic crystal.
  • FIG. 2 is a schematic depiction of sampling locations on a surface of a photonic crystal.
  • FIG. 3A is a graph showing reflectance spectra obtained from a photonic crystal having fluoropolymer and polystyrene dielectric layers and sampled at the locations schematically depicted in FIG. 2.
  • FIG. 3B is a graph showing reflectance spectra obtained from a photonic crystal having fluoropolymer and PVK dielectric layers and sampled at the locations schematically depicted in FIG. 2.
  • FIG. 4A is a graph showing P-polarized transmittance spectra obtained from the photonic crystal of FIG. 3A and sampled at the locations schematically depicted in FIG. 2.
  • FIG. 4B is a graph showing S-polarized transmittance spectra obtain from the photonic crystal of FIG. 3A and sampled at the locations schematically depicted in FIG. 2.
  • FIG. 4C is a graph showing P-polarized transmittance spectra obtained from the photonic crystal of FIG. 3B and sampled at the locations schematically depicted in FIG. 2.
  • FIG. 4D is a graph showing S-polarized transmittance spectra obtain from the photonic crystal of FIG. 3B and sampled at the locations schematically depicted in FIG. 2.
  • FIG. 5 is a graph showing reflectance spectra obtained from a photonic crystal having 3 repeat layers and sampled at the locations shown in the inset, the inset showing a schematic representation of sampling locations on the surface of the photonic crystal having 3 repeat layers.
  • FIG. 6 is a schematic representation of sampling location on the surface of a fluoropolymer monolayer fabricated by spin-coating at various speeds.
  • FIG. 7A is a graph showing reflectance spectra obtained from a fluoropolymer monolayer fabricated by spin-coating at 1200 rpm and sampled at the locations schematically depicted in FIG. 6.
  • FIG. 7B is a graph showing reflectance spectra obtained from a fluoropolymer monolayer fabricated by spin-coating at 3600 rpm and sampled at the locations schematically depicted in FIG. 6.
  • FIG. 7C is a graph showing reflectance spectra obtained from a fluoropolymer monolayer fabricated by spin-coating at 4800 rpm and sampled at the locations schematically depicted in FIG. 6.
  • FIG. 8A is a schematic representation of a horizontal experimental set-up to obtain temperature profiles of photonic crystals.
  • FIG. 8B is a schematic representation of a vertical experimental set-up to obtain temperature profiles of photonic crystals.
  • FIG. 9A is a graph showing temperature profiles obtained from 2 glass samples, a photonic crystal having fluoropolymer and polystyrene dielectric layers, and a photonic crystal having fiuoropolymer and PVK dielectric layers, where the temperature profiles were obtained from the horizontal experimental set-up schematically depicted in FIG. 8A and where the inset is a schematic depiction of the sampling location on the surface of the photonic crystal.
  • FIG. 9B is an enlargement of FIG. 9A, showing the region between 0 and
  • FIG. 9C is an enlargement of FIG. 9A, showing the region between 28.5° C and 30.5° C.
  • FIG. 10A is a graph showing the temperature profiles obtained from the glass samples and photonic crystals of FIG. 9A, where the temperature profiles were obtained from the vertical experimental set-up schematically depicted in FIG. 8B and wherein the inserts are schematic depictions of the sampling location on the surface of the photonic crystal having polystyrene dielectric layers (left inset) and of the photonic crystal having PVK dielectric layers (right inset).
  • FIG. 10B is an enlargement of FIG. 10A, showing the region between 0 and 0.1 minutes.
  • FIG. IOC is an enlargement of FIG. 10A, showing the region between 42° C and 50° C.
  • FIG. 11 A is a graph showing plots of T samp i e /T g i ass generated from the temperature profiles displayed in FIG. 9A.
  • FIG. 11B is a graph displaying plots of AT samp i e /AT g i ass generated from the temperature profiles displayed in FIG. 9A.
  • FIG. 12A is a graph showing plots of T samp i e /T g i ass generated from the temperature profiles displayed in FIG. 10A.
  • FIG. 12B is a graph displaying plots of AT samp i e /AT g i ass generated from the temperature profiles displayed in FIG. 10A.
  • FIG. 13A is a graph displaying plots of reflectance spectra of a one- dimensional photonic crystal having one repeat unit over a wavelength range between about 200 and about 1070 nm.
  • Fig. 13B is a graph reflectance spectra of the one-dimensional photonic crystal of FIG. 13A over a wavelength range between about 960 nm and about 2500 nm.
  • FIG. 14A is a graph displaying reflectance spectra of a one-dimensional photonic crystal having two repeat units over a wavelength range between about 200 and about 1070 nm.
  • Fig. 14B is a graph displaying reflectance spectra of the one-dimensional photonic crystal of FIG. 14A over a wavelength range between about 960 nm and about 2500 nm.
  • FIG. 15A is a graph displaying reflectance spectra of a one-dimensional photonic crystal having three repeat units over a wavelength range between about 200 and about 1070 nm.
  • Fig. 15B is a graph displaying reflectance spectra of the one-dimensional photonic crystal of FIG. 15A over a wavelength range between about 960 nm and about 2500 nm.
  • FIG. 16A is a graph displaying reflectance spectra of a fluorinated polymer monolayer deposited using a spin speed of about 4800 rpm.
  • FIG. 16B is a graph displaying reflectance spectra of a fluorinated polymer monolayer deposited using a spin speed of about 7200 rpm.
  • One-dimensional planar photonic crystals having significantly increased reflectance efficiency can be formed from optical materials including a fluoropolymer composition.
  • the one- dimensional photonic crystals described herein include an interface between different optical materials having different indexes of refraction, where at least one of the optical materials includes an amorphous fluoropolymer.
  • the one- dimensional photonic crystals described herein have a periodic structure formed from alternating layers of optical materials in which at least one of the alternating layers includes an amorphous fluoropolymer.
  • the relatively high dielectric contrast of the one-dimensional photonic crystals can provide desirable levels of reflectivity while incorporating a relative few number of dielectric layers.
  • the one-dimensional photonic crystals described herein are formed by sequential deposition of the optical materials. In some such embodiments, specifically adapted solution and post-deposition processing techniques can be used to promote desirable properties of the interfaces between the optical materials. Additionally, the one-dimensional photonic crystals described herein can provide desirable levels of thermal shielding to underlying substrates.
  • Photonic crystals involve optical structures having a periodic arrangement of optical materials having different refractive indexes.
  • the refractive index of a photonic crystal is spatially periodic.
  • the period can be comparable to that of the wavelength of visible light.
  • the optical materials are dielectric materials and, therefore, the optical materials are also referred to as dielectric materials when describing photonic crystals.
  • the photonic crystals described herein are one-dimensional photonic crystals and, correspondingly, have a refractive index that is periodic in a single dimension.
  • One-dimensional photonic crystals have a structure formed from repeating layers of dielectric layers, where the dielectric layers in the repeating layers have different refractive indexes.
  • the differences in the refractive indexes of the alternating dielectric layers form a photonic band gap along a single dimension. Based at least in part on the band gap, photons of some frequencies are transmitted (modes) through the photonic crystals and some frequencies are reflected.
  • the group of transmitted frequencies are referred to as allowed bands (to photon propagation) and the group of reflected frequencies is referred to as a photonic band gap (or forbidden bands).
  • the one-dimensional photonic crystals of interest herein have repeating units, each including at least two dielectric layers with different refractive indexes, where at least one of the dielectric layers in the repeating layers includes at least one fiuoropolymer.
  • the periodic arrangement of the repeating layers (or repeating units) can be referred to as a "stacked configuration.”
  • FIG. 1 is a schematic depiction of one embodiment of a one-dimensional photonic crystal according the present description. Referring to FIG. 1, photonic crystal 100 includes periodic repeating layers 102 (for clarity, only a first repeating unit is labelled). Repeating layers 102 include first dielectric layers 104 and a second dielectric layers 106 with respective widths 108, 110.
  • First dielectric layers 104, second dielectric layers 106 or both include a fiuoropolymer.
  • First dielectric layers 104 and second dielectric layers 106 have respective indexes of refraction ni and n 2 , 3 ⁇ 4 ⁇ n 2 .
  • a band gap is formed, in part, along the length "L" of photonic crystal 100 and in the direction represented by axis 112. Photons of allowed modes can be transmitted through photonic crystal 100 in a direction along axis 112. Photons having a frequency in the photonic band gap are reflected.
  • the one-dimensional photonic crystals can have repeating units including more than two dielectric layers.
  • one, some or all of the repeating can have 3, 4, 5, 6, 7, 8, 9, 10, 100 or more distinct dielectric layers.
  • the one-dimensional photonic crystals of interest herein can have at least 5 repeat units and no more than 200, 100, 90, 80, 70, or 50 repeat units.
  • the one-dimensional photonic crystals of interest herein can have a two or more sets of repeating units.
  • each repeating unit of each set includes at least two dielectric layers with different indexes of refraction.
  • at least one of the dielectric layers in each repeating unit includes at least one fluoropolymer.
  • a first set of repeat units can include dielectric layers A and B and a second set of repeat units can include dielectric layers C and D, where composition A includes a fluoropolymer.
  • the one dimensional photonic crystal can be schematically represented as: (AB) N (CD) M , where N and M are the number of repeat units AB and CD, respectively.
  • the one-dimensional photonic crystals of interest here can have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 100 or more sets of repeat units.
  • a person of ordinary skill will recognize additional ranges of number of sets of repeat units within the explicitly disclosed ranges are contemplated and within the scope of the present disclosure.
  • photonic crystals having repeat units including a dielectric layer having at least one fluoropolymer layer can have significantly improved efficiency, relative to corresponding photonic crystals having a non-fluorinate polymer layer.
  • photonic crystals having a larger number of repeat layers have a larger reflectivity, relative to corresponding photonic crystals have a smaller number of repeat layers.
  • the photonic crystals described herein can have significantly improved dielectric contrast and, correspondingly, the same or improved reflectivity as a corresponding photonic crystals having non-fluorinated polymer compositions, while including a fewer number of repeat units.
  • the photonic crystals described herein can have increased reflectivity relative to corresponding photonic crystals having only non-fluorinated polymer compositions, while including the same number of repeat units. Furthermore, because of the increased dielectric contrast, the on-dimensional photonic crystals described herein have an increased photonic band gap, relative to corresponding one- dimensional photonic crystals free of the fluoropolymer.
  • the optical devices described herein can be formed by depositing precursor solutions using conventional deposition techniques.
  • the dielectric compositions can be formed as precursor solutions that are sequentially deposited to form alternating dielectric layers using conventional deposition techniques including, but not limited to, spin coating, spray coating, knife edge coating or other appropriate techniques.
  • the precursor solutions can be deposited using printing techniques including, but not limited to, screen printing, inkjet printing and like. Deposition approaches including printing techniques can facilitate patterning of the precursor solution, although patterning can also be performed using a spin coating, spray coating or knife edge coating technique in conjunction with masks having appropriate geometries. Notwithstanding the particular deposition technique, after deposition, removal of at least a portion of the solvent from the deposited precursor solution can stabilize the deposited optical material.
  • the deposited precursor solution can be heated to remove at least a portion of the solvent.
  • the resulting cured layer is generally sufficiently stable for further processing including, but not limited to, deposition of another optical layer on top of or adjacent to the cured layer.
  • specifically adapted processing techniques can improve the reflective and structural properties of the photonic crystals.
  • specifically adapted deposition techniques and specifically adapted surface treatment techniques can be integrated into the processing approach to provide for improved layer thickness uniformity and improved adhesion between the fluoropolymer layers and the non-fluoropolymer layers, respectively.
  • any conventional method can be used to deposit the dielectric materials
  • specifically adapted spin coating approaches can aid in the formation of more uniform dielectric layers with a more narrow distribution of refractive indexes.
  • photonic crystals formed from the sequential deposition of dielectric materials by the specifically adapted spin coating techniques described herein can have a more uniform spatial reflectivity.
  • specifically adapted post deposition layer processing techniques can also be used to enhance the structural stability of the photonic crystal by enhancing the mechanical strength and optical uniformity of the interface between the dielectric layers.
  • the first dielectric layer can be plasma treated to enhance the adhesion between the first dielectric layer and the subsequently deposited second dielectric material.
  • Specifically adapted interlayer plasma processing as just described can also promote the optical performance of the photonic crystal by providing a more uniform interface between dielectric layers of different refractive indexes.
  • the one dimensional photonic crystals of interest herein can also have significantly improved thermal shielding for relatively thin photonic crystal structures.
  • relative thin photonic crystals can provide a significant degree of thermal shielding to an underlying substrate.
  • the one dimensional photonic crystals can reflect near-IR radiation that would otherwise be absorbed by the underlying substrate.
  • many electronic devices including but not limited to mobile devices (e.g. mobile phones, tablets, laptops, watches etc.) are used outdoors. These devices can absorb solar radiation and heat-up.
  • the one- dimensional photonic crystals described herein can reflect some or all of the near-IR portion of the incident solar radiation away from the devices to keep them at lower temperature. Reduced operating temperatures can help prevent damage to the electronic device and can help improve performance. Similar benefits to thermal shielding can be attained in photovoltaic (PV) modules, where higher temperatures lead to the reduction of the conversion efficiency, especially in the case of silicon based PV modules.
  • PV photovoltaic
  • the one-dimensional photonic crystals described herein can have from about 1 repeat unit to about 50 repeat units, from about 1 repeat unit to about 20 repeat units or from about 1 repeat unit to about 10 repeat units and can have a thermal shielding of from about 5% to about 95%, from about 5% to about 75%, from about 5% to about 50%, from about 5% to about 40% or from about 5% to about 30% thermal shielding in the near infrared spectrum (about 800 nm to about 3000 nm).
  • the one-dimensional photonic crystals described herein can have from about 1 repeat unit to about 50 repeat units, from about 1 repeat unit to about 20 repeat units or from about 1 repeat unit to about 10 repeat units and can have a thermal shielding of no less than about 5%, no less than about 10%, no less than about 20%, no less than about 40%> or no less than about 10% in the near infrared spectrum.
  • Thermal shielding can be measured by irradiating a photonic crystal, at room temperature, with light having a power of about 150 W, a colour temperature of about 3500 K and a spot diameter of about 4.75 mm.
  • the temperature of the photonic crystal can be monitored at an opposite surface (relative to the irradiated surface) to determine when the temperature of the photonic crystal is equilibrated.
  • the same measurement can be repeated on a glass sample having substantially similar dimensions to the photonic crystal.
  • the difference in equilibrated temperatures of the photonic crystal and glass substrate, relative to the equilibrated temperature of the glass substrate, can be multiplied by 100 and defined as the percent thermal shielding.
  • the one-dimensional photonic crystals described herein include repeating units of dielectric layers, as explained above.
  • the repeating units include at least a first dielectric layer having a fiuoropolymer and an adjacent second, distinct dielectric layer.
  • the second dielectric layer can include a (fluoro)polymer.
  • the photonic bandgap of the photonic crystal can be specifically engineered by appropriate selection of the compositions and thicknesses of the dielectric layers.
  • the photonic band gap of the photonic crystal can be characterized by a central frequency and a width.
  • one-dimensional photonic crystals reflect wavelengths that are about twice the optical distance of the periodicity of the repeating layers.
  • the thickness of the dielectric layers are selected to be about 1 ⁇ 4 of the central frequency of the desired photonic bandgap, taking into account the refractive index. For example, in application settings where near IR reflection is desirable (e.g.
  • Layer thickness can be optically measured using techniques known in the art including, but not limited to, reflectance and transmittance spectroscopy, ellipsometry, profilometry and interference microscopy. With respect to transmittance spectroscopy, light incident on the top surface of a film is reflected by the top surface as well as the opposite bottom surface. The reflections and transmissions correspondingly produce interference patterns that give rise to fringes. Based upon the number of the fringes, the thickness of the dielectric layer can be determined according to the following formula:
  • ⁇ and ⁇ 2 are, respectively, the minimum and maximum incident wavelength
  • n is the index of refraction of the dielectric layer
  • N is the number of fringes in the interference pattern
  • ⁇ is the angle of incidence of the incoming light beam relative to the plane of the top surface of the dielectric layer
  • t is the thickness of the dielectric layer.
  • the average thickness of a dielectric layer can be determined by measuring the thickness of the dielectric layer at various points along the top surface of the layer and averaging the measurement results.
  • the composition of the dielectric layers can be selected to engineer the width of the photonic bandgap.
  • the composition of the dielectric layer affects the indexes of the refraction of the layer and, correspondingly, affects the width of the photonic bandgap.
  • the width of the photonic bandgap can be estimated by the following formula:
  • the first dielectric layer can have a refractive index of greater than about 1 , or from about 1.1 to about 1.6, from about 1.1 to about 1.5, from about 1.2 to about 1.45, or from about 1.2 to about 1.4.
  • the refractive index of greater than about 1 can be greater than about 1 , or from about 1.2 to about 1.9, from about 1.3 to about 1.7, from about 1.35 to about 1.7, or from about 1.4 to about 1.7.
  • inorganic based second dielectric layers can have an index of refractions that is greater than about 1.3, or from about 1.3 to about 7, from about 1.3 to about 5 or from about 1.4 to about 5.
  • the composition of the first and second dielectric layers can be selected such that
  • can be within the aforementioned ranges.
  • the composition of the first and second dielectric layer is chosen such that n 2 > 3 ⁇ 4 and in other embodiments, is chosen such that 3 ⁇ 4 > n 2 .
  • can be within the ranges described above. A person of ordinary skill in the art will recognize that additional ranges of indexes of refraction and
  • the one-dimensional photonic crystals of interest herein can have a band gap from about 300 nm to about 3000 nm, from about 400 nm to about 2500 nm, from about 800 nm to about 2000 nm, from about 800 nm to about 1700 nm or from about 600 nm to about 1700 nm.
  • the one-dimensional photonic crystals of interest herein can have a first order band gap of from about from about 500 nm to about 3000 nm, from about 500 nm to about 2000 nm, or from about 800 nm to about 1700 nm.
  • the on-dimensional photonic crystals of interest herein can have a second order band gap from about 500 nm to about 2000 nm, from about 500 nm to about 1500 nm, from about 500 nm to about 1500 nm or from about 600 nm to about 1300 nm.
  • the width (full width half maximum ("FWHM")) of the first diffraction order band gap can be from about 50 nm to about 500 nm, from 100 nm to about 500 nm or from about 100 nm to about 400 nm or from about 100 nm to about 300 nm.
  • Higher order band gaps e.g.
  • second order, third order, etc. can have a FWHM within the same ranges as described for first diffraction order band gaps.
  • a person of ordinary skill in the art will recognized additional ranges of band gaps and widths within the explicitly disclosed ranges are contemplated and within the scope of the present disclosure.
  • the one- dimensional photonic crystals incorporating repeating units including at least one dielectric layer having a fluoropolymer composition have significantly improved efficiency with respect to reflectivity.
  • the presently described photonic crystals can achieve the same or greater reflectivity with a smaller number of repeat units.
  • increasing the number of repeat units in a one dimension photonic crystal increases the amount the incident light reflected.
  • the photonic crystals can have at least 1 repeat unit or at least 5 repeat units and no more than 200 repeat units, no more than 100 repeat units, no more than 50 repeat units, no more than 30 repeat units, no more than 20 repeat units, no more than 15 repeat units, no more than 13 repeat units, no more than 10 repeat units, no more than 9 repeat layers or no more than 7 repeat units.
  • the one-dimensional photonic crystals can have from 5 to 200 first dielectric layers and from 5 to 200 second dielectric layers; from 5 to 100 first dielectric layers and from 5 to 100 second dielectric layer; from 5 to 50; 5 to 30 first dielectric layers and 5 to 30 second dielectric layers; 5 to 15 first dielectric layers and 5 to 15 second dielectric layers; or 5 to 10 first dielectric layers and 5 to 10 second dielectric layers; where the dielectric layers are in an alternating stacked configuration.
  • the one-dimensional photonic crystals of interest herein have a reflectivity of at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% or at least 98%, for a wavelength from about 300 nm to about 3000 nm, from about 400 nm to about 2500 nm, from about 800 nm to about 2000 nm, form about 800 nm to about 1700 nm or from about 600 nm to about 1700 nm.
  • the one-dimensional photonic crystals of interest herein can have at least 10 repeat units where 10 sequential repeat units have a reflectivity of at least 70%, at least 80%, at least 90%, at least 92% or at least 95%, for a wavelength between about 800 nm to about 1700 nm.
  • 10 sequential repeat units have a reflectivity of at least 70%, at least 80%, at least 90%, at least 92% or at least 95%, for a wavelength between about 800 nm to about 1700 nm.
  • the thickness of the dielectric layers can be selected to engineer a desired band gap, with respect to the dielectric constant of the dielectric layers. Based upon the present disclosure, a person of ordinary skill in the art will know how to select appropriate dielectric layer thicknesses based on the intended application setting of the one-dimensional photonic crystal (e.g., based upon the desired band gap for the application setting).
  • the first dielectric layer or second dielectric layer can have a thickness (e.g. 108, 1 10 of FIG. 1) of from about 50 nm to about 5 ⁇ , from about 50 nm to about 2 ⁇ , from about 100 nm to about 2 ⁇ , from about 200 nm to about 2 ⁇ or from about 200 nm to about 1 ⁇ .
  • a person of ordinary skill in the art will recognize additional thickness ranges within the explicitly disclosed ranges are contemplate and within the scope of the present disclosure.
  • the one-dimensional photonic crystals of interest herein include repeating layers including at least a first dielectric layer and an adjacent second dielectric layer.
  • the first dielectric layer includes a first dielectric composition including a fluoropolymer, and has a bulk refractive index, 3 ⁇ 4 .
  • the first dielectric composition can optionally include other components that promote improved optical or mechanical properties or processing characteristics of the composition.
  • the second dielectric layer includes a second dielectric composition and has a bulk refractive index n 2 ⁇ 3 ⁇ 4 .
  • the second dielectric layer includes an organic or nonorganic composition and can also include other components as described above.
  • the first dielectric composition includes one or more fluoropolymers and, optionally, one or more additional components.
  • fluoropolymers include polymers having a recurring unit that includes at least one fluorine atom.
  • a first class of fluoropolymers appropriate for use in the first dielectric layer includes amorphous fluoropolymers having alicyclic structures in the polymer main chain.
  • amorphous fluoropolymers refer to fluoropolymers that are substantially free of any internal crystal structure and, in particular, have a heat of fusion lower than 5 J/g as determined by differential scanning calorimetry ("DSC") according to ASTM D3418-08.
  • amorphous fluoropolymers having alicyclic structures in the polymer main chain are described in, EP 803557 A to Avataneo et al., filed October 19, 2012, describing amorphous fluoropolymers having recurring units derived from at least one fluorinated monomer having alicylcic structres in the polymer main chain, recurring units derived form at least one fluorinated monomer having an - S0 2 X functional group and, optionally, recurring units derived from at least one ethylenically unsaturated fluorinated monomer; EP 1256591 A to Tortelli et al., filed April 25, 2002, describing amorphous fluoropolymers in including perfluorinated polymers; EP 645406 A to Squire, filed May 31 , 1988, describing amorphous copolymers of perfluoro-2,2-dimethyl-l,3-dioxole; and EP 303298 A to Nakamur
  • the amorphous fluoropolymer including alicyclic structures in the polymer main chain can have recurring units derived from at least one fluorinated monomer selected from the group consisting of:
  • Ri, R 2 , R 3 and R 4 are independently selected from the group consisting of -F, a Ci-C 6 fluoroalkyl, optionally including one or more oxygen atoms, a Ci- C 6 fluoroalkoxy, optionally including one or more oxygen atoms; the fluorodioxo lanes of formula (II):
  • R5 and R 6 are independently selected from the group consisting of -F, a Ci-C 6 fluoroalkyl, optionally including one or more oxygen atoms, a Ci- C 6 fluoroalkoxy, optionally including one or more oxygen atoms; and
  • each R 7 to Ri 6 independently of one another, is selected from -F, and a Ci-C 3 fluoroalkyl, a is 0 or 1 , b is 0 or 1 with the proviso that b is 0 when a is 1.
  • the fluoropolymers including alicyclic structures in the polymer main chain suitable for the first dielectric component are those selected from the group consisting of:
  • Ri, R 2 , R 3 and R 4 equal to or different from each other, are independently selected from the group consisting of -F, a Ci-C 6 fiuoroalkyl, optionally including one or more oxygen atoms, a Ci-C 6 fluoroalkoxy, optionally including one or more oxygen atoms; preferably wherein Ri, R 2 , R3 and R 4 , equal to or different from each other, are independently selected from the group consisting of -F, a C 1 -C3 perfluoroalkyl, e.g.
  • the fluoropolymers including alicyclic structures in the polymer main chain for the first dielectric component are those selected from the group consisting of:
  • amorphous fluoropolymers including recurring units derived from fluorodioxoles of formula (I) or from monomers of formula (III) and of interest herein can have a bulk refractive index npp of from about 1.250 to about 1.350 or from about 1.298 to about 1.334.
  • npp bulk refractive index
  • a second class of fluoropolymers suitable for use in the first dielectric layer include elastomers having fluoropolyether chains.
  • the elastomer can obtained by the UV-curing of compositions including: at least one functional fluoropolyether compound having a fluoropolyoxyalkylene chain (R f ) and having at least two unsaturated moieties; and at least one photoinitiator, as described in WO 2010/094661 to Koo et al , filed February 16, 2010, which is incorporated herein by reference.
  • the functional fluoropolyether compound can be selected among those compounds of formula (IV):
  • Tj-J-R f J' -T 2 (IV) - R f represents a fluoropolyoxyalkylene chain including recurring units having general formula: -(CF 2 ) k -CFZ-0-, wherein k is an integer of from 0 to 3 and Z is selected between a fluorine atom and a C1-C 5 perfluoroalkyl group, optionally including one or more oxygen atom; preferably chain R f complies with formula: - (CF 2 0) p (CF 2 CF 2 0) q (CFYO) r (CF 2 CFYO) s -(CF 2 (CF 2 ) z CF 2 0)t- wherein Y is a C1-C 5 perfluoroalkyl group, optionally including one or more oxygen atom, z is 1 or 2; and p, q, r, s, t are integers > 0; chain R f more preferably complies with formula:
  • T 2 - Ti and T 2 are selected from the group consisting of:
  • R H is H or a Ci-C 6 alkyl group
  • R A is selected from the group consisting of:
  • R is a divalent group selected from the group consisting of C1-C10 aliphatic group, C5-C14 cycloaliphatic group; C 6 -Ci4 aromatic or alkylaromatic group.
  • chain R f has preferably an average molecular weight between 1000 and 3000, more preferably between 1 100 and 3000, even more preferably between 1 100 and 2500; it is thus understood that in corresponding preferred structures as above detailed p, q, r, s, t, p ' and q' represent integers selected so as to comply with these molecular weight requirements.
  • p, q, r, s, t, p ' and q' represent integers selected so as to comply with these molecular weight requirements.
  • suitable compounds of formula (IV) can be selected from the group consisting of:
  • compositions suitable for the preparation of elastomeric polymers by UV curing are commercially available from Solvay Specialty Polymers Italy SpA under the trade name Fluorolink ® , e.g. Fluorolink ® MD500 PFPE.
  • Fluorolink ® e.g. Fluorolink ® MD500 PFPE.
  • the elastomeric polymers obtainable by UV curing of a functional fluoropolyether compound of formula (IV) of interest herein have a bulk refractive index npp of from about 1.250 to about 1.350.
  • fluoroelastomers are amorphous polymers and have a glass transition temperature ("T g ”) below room temperature, in most cases even below 0° C.
  • T g glass transition temperature
  • Suitable fluoroelastomers advantageously comprise recurring units derived from vinylidene fluoride and/or from tetrafiuoroethylene.
  • the fluoroelastomer used as the first dielectric component in the photonic crystal of the invention consists of recurring units derived from vinylidene fluoride and/or from tetrafiuoroethylene and at least one other fluorinated monomer.
  • suitable fluorinated monomers can be selected from:
  • the fluoroelastomer can optionally contain recurring units derived from C 3 -Cs fluoroolefins, optionally containing hydrogen atoms, chlorine and/or bromine and/or iodine, C 2 -C8 non- fluorinated olefins, preferably ethylene and/or propylene.
  • the fluoroelastomers of the first dielectric layer can include those described in U.S. 5,585,449 ('"449”) to Arcella et al, filed December 22, 1994, describing fluoroelastomers including monomeric layers deriving form a bis-olefin; U.S. 5,264,509 to Arcella et al.
  • the fluoroelastomer can optionally contain from 0.01 to 1 mol% of recurring units derived from bis- olefins.
  • Non-limiting examples of suitable fluoroelastomers include, but are not limited to copolymers of vinylidene fluoride, hexafluoropropene, tetrafluoroethylene and perfluoroalkyl vinyl ethers; copolymers of vinylidene fluoride, hexafluoropropene and optionally tetrafluoroethylene; copolymers of vinylidene fluoride, perfluoroalkyl vinyl ether, and optionally tetrafluoroethylene; copolymers of vinylidene fluoride, C 2 -Cs non-fluorinated olefins, hexafluoropropylene and/or perfluoroalkyl vinyl ether and tetrafluoroethylene; copolymers including vinylidene fluoride and fluoromethoxyvinyl ether and optionally perfluoroalkyl vinyl ether and tetrafluoroethylene ; copolymers of
  • desirable fluoroelastomers for the first dielectric layer can be selected from the group consisting of: copolymers of vinylidene fluoride (55-85 mol%), hexafluoropropene (15-45 mol%) and optionally tetrafluoroethylene (0-30 mol%); copolymers of vinylidene fluoride (50-80 mol%), perfluoroalkyl vinyl ether (5-50 mol%), and optionally tetrafluoroethylene (0-20 mol%); copolymers of vinylidene fluoride (20-30 mol%), C 2 -Cs non-fluorinated olefins (10-30 mol%), hexafluoropropylene and/or perfluoroalkyl vinyl ether (18-27 mol%) and tetrafluoroethylene (10-30 mol%); copolymers including vinylidene fiuoride (50-80 mol%) and fluoromethoxyvinyl ether (20-50-50 .
  • Fluoroelastomers suitable for the photonic crystals described herein are commercially available under the trade name TECNOFLON ® (Solvay Specialty Polymers Italy SpA), TECNOFLON ® PFR (Solvay Specialty Polymers Italy SpA), VITON ® (Du Pont), KALREZ ® (Du Pont), DAIEL ® (Daikin), FLUOREL ® (Dyneon, 3M).
  • the bulk refractive index npp of fluoroelastomers of interest herein is from about 1.320 to about 1.400.
  • a fourth class of suitable fluoropolymers for use in the first dielectric component are those selected from the group consisting of fluorosilicone rubbers ("FVMQ"), for example, those described in PIERCE, O.R., et al, “Fluorosilicone rubber,” Industrial and Engineering Chemistry Research, 1960, vol.52, p.783-784 and in Cornelius, D.J., et al , "The unique properties of silicone and fluorosilicone elastomers," Polym. 1985, vol.25, p.467-473, both of which are incorporated by reference herein.
  • FVMQ fluorosilicone rubbers
  • Fluorosilicone rubbers can include contain recurring units of formula (V):
  • RF is a Ci-C 6 fluoroalkyl, typically -CH 2 CH 2 CF 3 .
  • Fluorosilicone rubbers suitable for the photonic crystals described herein are commercially available under the trade name Silastic ® (Dow Corning), FQE ® /FSE ® (Momentive Performance Materials), FE ® (Shin-Etsu), ELASTOSIL ® FLR (Wacker).
  • the fluoropolymer for the first dielectric layer is desirably selected from the groups consisting of the fluoropolymers including alicyclic structures in the polymer main chain and the elastomers including fluoropolyether chains as defined above.
  • the first dielectric composition can include one or more additional components, including but not limited to, viscosity modifiers, solvents, emulsifiers, organic and inorganic fluorophores, phosphorescence and chemiluminescent materials, non-linear optical materials, charge transport dopants, chemical receptors, and any combination thereof.
  • the first dielectric composition consists essentially of one or more fluoropolymers. When the first dielectric compositions includes more than one fluoropolymer and/or includes one or more additional components as described above, then the effective refractive index 3 ⁇ 4 of the first dielectric component can be determined according to the suitable effective medium approximation as discussed in GHER, R.J., et al.
  • the total concentration of the one or more fluoropolymers in the first dielectric composition is from about 50 weight percent ("wt%") to about 99 wt%, from about 60 wt% to about 95 wt%, from about 70 wt% to about 95 wt%, or from about 80 wt% to about 95 wt%, relative to the total weight of the first dielectric composition.
  • the toatl concentration of the one or more fluoropolymers is at least 60 wt%, at least 70 wt%, at least 85 wt%, at least 90 wt%, at least 95 wt% or at least 97 wt%, relative to the total weight of the first dielectric composition.
  • the second dielectric layer composition can be an organic or an inorganic composition.
  • organic materials for the second dielectric layers described herein include, but are not limited to polymeric materials, in particular polymeric materials having a refractive index n 2 - 3 ⁇ 4 is at least 0.001.
  • the second dielectric layer includes an organic material selected from the group consisting of poly(methyl methacrylate), polycarbonate, polystyrene, cellulose acetate and poly(vinyl carbazole).
  • the one dimensional photonic crystals described herein can be fabricated by sequential deposition of precursor solutions, formed from the dielectric layer compositions, onto a substrate.
  • specifically adapted solution processing techniques can promote the formation of dielectric layers having significantly improved optical performance.
  • specifically adapted plasma processing techniques can be used to increase the mechanical stability and optical performance of the photonic crystals described herein.
  • the composition of the substrate can be selected based on the desired application of the one dimensional photonic crystal.
  • the substrate can include, but is not limited to, silicon wafers, silica substrates, glass substrates, other inorganic material substrates, polymer substrates (e.g., organic polymer substrates), composites thereof and combinations thereof across a surface and/or in layers of the substrate.
  • Polymer substrates or polymer coated substrates can be particularly desirable in application sections requiring flexibility and appropriate polymers can be selected with respect to processing temperatures.
  • Appropriate polymers include, but are not limited to, polycarbonates, polyimides, polyesters, polyalkenes, copolymers thereof and mixtures thereof. For optical applications, it can be particularly desirable for the substrate to have a relatively flat surface.
  • the substrate can be an optical device, or a portion thereof, and the one-dimensional photonic crystal can be formed as an integrated component of the optical device.
  • the substrate can be a support upon which free-standing one- dimensional photonic crystal is fabricated.
  • the one dimensional photonic crystal can be separated from the substrate and, optionally, integrated into an optical device or other device with further processing.
  • any suitable coating process can be used to deposit the precursor solution of the dielectric layer compositions onto a substrate.
  • the precursor solutions can be spin-coated, spray-coated, dip coated, knife edge coated or printed.
  • Printing approaches include, but are not limited to, inkjet printing and screen printing.
  • the one dimensional photonic crystals are formed by sequentially depositing precursor solutions to sequentially form the first and second dielectric layers.
  • Each dielectric layer can be formed by performing one or more spin-coating steps to achieve the desired thickness of the layer.
  • the deposited precursor solution can be thermally processed to stabilize the layer with respect to further processing including, but not limited to, deposition of the same or a different precursor solution.
  • dielectric layers with significantly improved uniformity can be formed using specifically adapted spin-coating approaches.
  • Spin-coating approaches involve placing a substrate on a rotating support, rotating the support at a selected frequency and depositing the precursor solutions at the location on the substrate surface corresponding to the axis of rotation. Such an approach is intended to promote complete coverage of the substrate with the precursor solution.
  • relatively small variations in layer thickness can translate into large variations in optical properties (e.g. reflectivity) along the surface of the layers.
  • small variations in layer thickness can promote large anisotropy in the optical properties of a dielectric layer.
  • the substrate can be spun at rates from about 100 revolutions per minute ("rpm") to about 20000 rpm, from about 200 rpm, to about 20000 rpm, from about 200 rpm to about 15000 rpm, from about 500 rpm to about 15000 rpm, from about 1000 rpm to about 10000 rpm, from about 2500 rpm to about 10000 rpm, from about 3000 rpm to about 9000 rpm, or from about 3000 rpm to about 7000 rpm.
  • the substrate can be spun for a duration from about 5 seconds to about 5 minutes, from about 10 seconds to about 4 minutes or from about 30 seconds to about 4 minutes.
  • an initial low speed spin can be used to perform an initial bulk spreading of the precursor solution across the surface of the substrate.
  • the substrate can be spun at between 10 rpm to about 200 rpm and for about 10 seconds to about 1 minute.
  • additional spin speeds and spin times within the explicitly disclosed ranges are contemplated and within the scope of the present disclosure.
  • the resulting films can have a thickness that varies no more than about 25%, no more than about 20%, no more than about 15%, no more than about 10%, no more than about 5% across the surface of the dielectric layer, relative to the average thickness of the dielectric layer.
  • the precursor solutions can be formed by creating a dispersion of the dielectric layer composition with one or more appropriate solvents.
  • any suitable solvent or solvent blend including a plurality of solvents can be used.
  • Suitable solvents include solvents that homogenous ly disperse the dielectric layer composition in the precursor solution, alone or in conjunction with a dispersant including, but not limited to a surfactant.
  • appropriate solvents homogenously disperse the dielectric layer composition so that it can be coated onto the substrate without an undesirable amount of settling/separation.
  • desirable qualities of the dispersions can depend on the polymer concentration, the dielectric layer composition and the formation of the dispersion.
  • suitable solvents can include, but are not limited to, water, organic solvents, such as alcohols and hydrocarbons, and combinations thereof.
  • suitable solvents can include, but are not limited to acetone, perfiuoropolyether fluids, hydrofluoroethers, or blends thereof. Desirable perfiuoropolyether ethers are commercially available as Galden® PFPE and Fomblin® PFPE from Solvay Specialty Polymers Italy SpA.
  • Desirable hydrofluoroethers are commercially available as NovecTM Fluids from 3M Corporation and include compositions represented by the formula C2nFn+i-OC n H 2 n+i .
  • the selection of desirable solvent can involve the selection of solvents having a relative low boiling point. Solvents having a relative low boiling point can be removed from the deposited dielectric layer composition with relatively mild thermal processing.
  • the solvent can have a boiling point of less than about 250° C, less than about 150° C, less than about 100° C, or less than about 80° C, less than about 60° C or less than about 40° C.
  • a person of ordinary skill in the art will recognize additional boiling point ranges within the explicitly disclosed ranges are contemplated and within the scope of the present disclosure.
  • the concentration of the dielectric layer composition in the precursor solution can be selected to achieve desirable precursor solution viscosities for the spin-coating deposition as described above.
  • the concentration of the dielectric layer composition in the precursor solution can be selected to achieve desirable viscosities for spin-coating deposition.
  • the concentration of the fluoropolymer in the precursor solution of the first dielectric composition can be between 0.01% to about 50%, from about 0.1%) to about 50%>, from about 0.5 to about 50%>, from about 0.1 to about 20%> from about 0.1 % to about 15%, or from about 0.1 % to about 10%> weight by volume (“wt./vol").
  • the deposited material after deposition of a dielectric layer composition, can be thermally processed (e.g. cured) to remove solvent and stabilize the deposited material for subsequent processing. In some embodiments, the deposited material can be heated to remove solvent. Removal of the solvent can alter the layer thickness as well as the concentration of the dielectric composition components in the ultimately formed dielectric layer. The effects of solvent removal can be accounted for in the design of the precursor solution and/or spin-coating recipe. In particular, to account for removal of solvent, the initial concentration of the dielectric composition components in the precursor solution and the amount of precursor solution deposited on the substrate can be adjusted. Based upon the present disclosure, a person of ordinary skill in the art will know how to empirically determine the degree of adjustment.
  • the deposited dielectric composition can be further processed. Further processing can include, but is not limited to, deposition of another dielectric composition, distinct or the same as the cured dielectric composition, on the cured dielectric composition; plasma treatment of the cured dielectric layer or a combination of both.
  • the dielectric layer can be plasma treated to improve the adhesion between polymeric based dielectric layers.
  • Plasma treatment involves subjecting the cured dielectric layer to plasma at an appropriate power density in a plasma chamber.
  • the plasma can clean the surface of a polymeric dielectric layer by, in part, removing organic contaminants at the surface.
  • the plasma can be a capacitatively coupled plasma ("CCP"). Relative to an inductively coupled plasma (“ICC”), CCPs can be less dense and result in more a more benign treatment of the dielectric layer.
  • the plasma can be formed by applying an electric field/electromagnetic field to a gas.
  • the gas can include or consist essentially of argon, oxygen, nitrogen or any combination thereof.
  • the field can include a DC field (e.g. continuous filed) or an AC field, such as a periodic field (e.g., an RF field).
  • the power of the resulting plasma can be at least partially determined by the amplitude of the voltage applied to the electrodes, as described further below.
  • the plasma power and treatment time can be selected to help reduce undesirable damage to the dielectric layer.
  • a polymer based dielectric layer can be exposed to a plasma having a power density of from about 1 W/L to about 100 W/L, from about 1 W/L to about 50 W/L, from about 1 W/L to about 20 W/L or from about 1 W/L to about 10 W/L.
  • a polymer based dielectric layer can be exposed to a plasma for a duration from about 1 second to about 20 minutes, from about 1 second to about 10 minutes, from about 1 second to about 5 minutes, from about 30 seconds to about 5 minutes, from about 30 seconds to about 3 minutes, or from about 50 seconds to about 3 minutes.
  • the plasma treatment can be performed in a plasma chamber having a pressure of no more than about 100 millibar ("mbar"), no more than about 10 mbar, no more than about 5 mbar or no more than about 1 mbar.
  • mbar millibar
  • power density refers to the average power of the plasma divided by the volume of the plasma chamber (e.g. vacuum chamber).
  • D l and where ⁇ Pcw> is the average power of the continuous wave plasma.
  • one-dimensional photonic crystals including at least one fluoropolymer-based dielectric layer in the repeating layers.
  • one dimensional photonic crystals consisting of repeat layers consisted of a fluoropolymer based dielectric layer and a second polymeric based dielectric layer were formed.
  • cellulose acetate and PVK were commercially obtained from Sigma- Aldrich and ThermoFisher, respectively.
  • precursor solutions of the fluoropolymer and non-fluorinated polymer were sequentially spin-coated to build the repeat layers.
  • the fluoropolymer was dispersed in a perfluoropolyether solvent (Galden ® PFPE HT110 commercially available from Solvay Specialty Polymers Italy SpA) to form a 2% wt./vol. - 10% wt./vol. solution of the fluoropolymer.
  • the non-fluorinated polymer was dispersed in toluene to form a 2% wt./vol. - 10% wt./vol. solution of the non-fluorinated polymer.
  • the precursor solution was spin-cast and, subsequently, cured (by heating) to remove solvent and form the dielectric layer (unless explicitly stated otherwise).
  • Spin coating was performed between 200 rpm and 12000 rpm and for about 2 minutes (unless explicitly stated otherwise).
  • the cured dielectric layer was subjected to plasma treatment to improve the adhesion between the dielectric layers of the ultimately formed one-dimensional photonic crystals.
  • Plasma treatment involved subjecting the cured dielectric layer to an air or oxygen plasma, at a power density of about 7.5 W/L for a duration of 10 seconds to 10 minutes.
  • the gas was flowed into the plasma chamber at a flow rate of about 24 standard cubic centimetres per minute ("seem") to maintain a pressure of about 0.5 mbar.
  • seem standard cubic centimetres per minute
  • the spin-coating deposition, curing, and plasma treatment of successive layers was repeated until the desired number of repeat layers (and repeat units) were formed.
  • This Example demonstrates the performance of one-dimensional photonic crystals including at least one fluoropolymer-based dielectric layer in the repeating layers.
  • 2 samples were formed, each consisting of 9 repeat layers.
  • the non-fluorinated polymer of samples 1 (Fig. 3A) and 2 (Fig. 3B) were, respectively, polystyrene and PVK.
  • the dielectric layers of sample 1 had a thickness of about 347 nm for the fluoropolymer based dielectric layer and 187 nm for the non-fluorinated polymer based dielectric layer, respectively.
  • the dielectric layers of samples 2 had a thickness of about 221 nm for the fluoropolymer based dielectric layer and 118 nm the non-fluorinated polymer based dielectric layer, respectively.
  • the fluoropolymer precursor solutions were formed by adding a selected amount of polymer to an appropriate solvent.
  • the fluorinated polymer precursor solutions were formed by adding 5g of Hyflon® AD60 to 100 ml of (Galden® HT 110).
  • the polystyrene and PVK precursor solutions were formed by adding 7.5 g of polystyrene and 5g of PVK, respectively, to 100 ml of toluene.
  • the fluorinated polymer dielectric layers 130 ⁇ _, of the corresponding precursor solution was deposited at the centre of the previous formed layer (or glass substrate for the first deposited layer) while spinning the glass substrate for about 2 minutes at 6000 rpm.
  • 150 ⁇ _, of the corresponding precursor solutions were spin-cast as just described but using a spin rate of about 9000 rpm.
  • the structure was cured on a hot plate at a temperature of about 80° C for about 2 minutes.
  • Plasmas treatment involved exposing the layers to an air plasma for 30 seconds with a power density of 7.5 W/L.
  • the ultimately formed one- dimensional photonic crystals had a thickness of about 4.5 micrometers (" ⁇ ") and about 3 ⁇ , for samples 1 and 2, respectively. Both samples had a length and width of about 2 cm.
  • Sample 1 had a band gap of about 1500 nm and sample 2 had a band gap of about 1000 nm.
  • Reflectance and transmittance spectra were obtained using optical fiber coupled AvaSpec ULS2048 spectrometers (200-1100 nm, resolution 1.4 nm) (commercially available from Avantes) and an ARCoptix FT-interferometer (900-2600 nm, resolution 8 cm "1 ).
  • the light source was a combined deuterium- halogen light source Micropak DH-200-BAL (commercially available from Ocean Optics. Reflectance and transmittance spectra were obtained using spot sizes of about 2 nm and 0.5 mm to about 5 mm.
  • FIG. 2 is a schematic depiction of the sampling points (each about 2 mm diameter) on the sample surface. Transmittance spectra were obtained for incidence angles of between about 0° and about 60°, relative to the plane defined by the sample surface.
  • FIGS. 3A and 3B and 4A - 4D are graphs showing wavelength versus reflectance (reflectance spectrum) and wavelength versus transmittance (transmittance spectrum), respectively, obtained from samples 1 and 2.
  • FIG. 3A is a graph showing a plots of incident wavelength vs. reflectance (reflectance spectrum) obtained from various locations about the surface of sample 1, as indicated in FIG. 2.
  • FIG. 3 A demonstrates that around the band gap of about 1500 nm, the sample had a 1 st order reflectance of at least about 85% and a second order reflectance of about 70% (at about 750 nm).
  • FIG. 3B is a graph showing the reflectance spectra from various location about the surface of sample 2, as indicated in FIG. 2.
  • FIG. 3A is a graph showing a plots of incident wavelength vs. reflectance (reflectance spectrum) obtained from various locations about the surface of sample 1, as indicated in FIG. 2.
  • FIG. 3 A demonstrates that around the band gap of about 1500 nm, the sample had a 1 st order reflectance of at least about 85% and a second order reflectance of about 70% (at about 750 nm).
  • FIG. 3B is a graph showing the reflectance spectra from
  • sample 2 had a first order reflectance of about 98% and second order reflectance (at about 500 nm) of about 68%. It is noted that for sampling locations E (in the center of each sample), the reflectance spectra of samples 1 and 2 exhibited significant spectral shift with respect to the other locations due to a lower thickness uniformity there achieved being such point the solution deployment site.
  • FIG. 4A is a graph showing plots of wavelength vs. transmittance (transmittance spectrum) of P-polarized light obtained from sample 1 at various incidence angles.
  • FIG. 4B is analogous to FIG. 4A and shows the transmittance spectra of S-polarized light.
  • the transmittance monotonically decreased with increased incidence angle, for both P- and S-polarized light.
  • the transmittance of the S-polarized components of the incident light was generally greater than that of the P-polarized light of the same wavelength. Similar results were obtained from the transmittance spectra of sample 2 as shown in FIGS. 4C and 4D, which are analogous to FIGS. 4A and 4B, respectively.
  • sample 3 a further sample consisting of 3 repeat layers.
  • the non-fluorinated polymer of sample 3 was polystyrene
  • the dielectric layers of sample 3 had an estimated average thickness of about 100 nm and 230 nm for the fluoropolymer based dielectric layer and the non-fluorinated polymer based dielectric layer, respectively. The thicknesses were estimated from thickness measurements made on similar samples (not shown).
  • the dielectric layers were formed as described above in this Example using a spin speed of 4200 rpm for both the fluoropolymer and non- fluoropolymer dielectric layers. Similarly, plasma treatment was performed as described above with respect to the polystyrene layers.
  • the ultimately formed one-dimensional photonic crystals had a thickness of about 1 micron and a length and width of about 2 cm.
  • reflectance spectra were obtained as described above. The reflectance spectra were obtained at various points along the surface of Sample 3, as indicated in the inset of FIG. 5.
  • FIG. 5 is a graph showing the reflectance spectra obtained from Sample 3. Referring to FIG. 5, the spectra show a significant second order reflectance (at about 1100 nm) of about 23% to about 37% and a fourth order reflectance (at about 380 nm) of from about 35% to about 43%. As explained above, the significant variation in the reflectance spectrum obtained at point H (center of the sample) likely reflects that Sample 3 is thicker in the central region relative to peripheral regions A - E.
  • Example 2 Effect of Fabrication Parameters on the Thickness of One- Dimensional Photonic Crystals
  • This example demonstrates the effect of Spin-Coating parameters on the average thickness of one-dimensional photonic crystal dielectric layers.
  • each sample consisted of a single dielectric layer formed from Hyflon® AD60 (fluoropolymer).
  • the precursor solutions consisted of about 2% wt./vol. to about 7.5% wt./vol. of the fluoropolymer.
  • 100 to about 200 ⁇ , of each precursor solution was spin coated onto a glass substrate using spin rate of from about 1200 rpm to about 7200 rpm and a spin time of about 2 minutes.
  • TABLE 1 shows the formation parameters of each of the samples.
  • samples prepared with increased spin speed and decreased fluoropolymer concentration had the smallest average thickness.
  • the average thickness of Samples 7 - 9 decreased from 280 nm to 170 nm when the spin speed was increased from 1200 rpm 3600 rpm.
  • the average thickness of Samples 10 - 13 decreased from 680 nm to about 360 nm when the spin speed was increased from 1200 rpm to 4800 rpm.
  • comparison of the average thickness of Samples 7 - 9 with Samples 1 1 - 13, respectively demonstrate that increasing the fluoropolymer concentration in the precursor solution increases the average thickness of the ultimately formed monolayer.
  • FIGs. 7A - 7C graphs showing the reflectance spectra of samples 13, 1 1 and 10, respectively, taken at the various points along the sample surface as depicted in FIG. 6.
  • spin speed 1200 rpm
  • the reflectance spectrum of Sample 13, obtained at point G is significantly different from the reflectance spectra obtained at points A - F. More particularly, the difference in the reflectance spectrum at point G appears to indicate that the monolayer of Sample 13 is thicker in the central region relative to the peripheral regions.
  • This Example demonstrates the thermal shielding by one-dimensional photonic crystals.
  • samples 1 and 2 were subjected to thermal shielding testing Thermal shielding was measured both horizontally and vertically, to facilitate thermal shielding measurements.
  • light having a power of about 150 W and a color temperature of about 3200 K centre wavelength of about 900 nm
  • a thermometer (Testo Mod.1 10 with a 6 mm diameter probe) was placed at the opposite surface and at a location corresponding to the target location. The thermal stability was evaluated by monitoring the temperature as a function of time while the incident light was directed at the target location.
  • FIGS. 8A and 8B are schematic representations of the respective horizontal and vertical experimental set-ups.
  • samples 902, 904 are supported on sample holder 906 and film 908 (grease film to improve adhesion of thermometer head to the substrate), respectively.
  • Fiber optic bundles 910, 912 are displaced away from the surfaces of respective films 902, 904 at a respective distance of about 3 cm and 5 cm.
  • Light exiting fiber optic bundles 910, 912 travels through respective samples 902, 904 to respective thermocouples 914, 916, which are in contact with respective samples 910, 912.
  • the temperature of the samples 902, 912 is monitored by respective thermocouples 914, 916.
  • Samples 14 and 15 were illuminated for about 11 minutes (horizontal thermal stability) and 30 minutes (vertical thermal stability) while the temperature of the samples were monitored.
  • horizontal thermal stability measurements were taken at a single location along the samples.
  • vertical thermal stability the samples were moved in the plane of the sample between the thermocouple and optical bundle to obtain measurements at 3 locations along the samples.
  • thermal stability measurements were also obtained for the bare glass substrate samples having dimensions that were substantially similar to those of Samples 14 and 15.
  • FIG. 9A is a graph showing plots of time versus temperature ("temperature profile") obtained from horizontal thermal measurements of Samples 14 and 15 and the glass references.
  • the inset of FIG. 9A is a schematic representation depicting the sampling area on surface of the samples.
  • FIGS. 9B and 9C are enlargements of FIG. 9A.
  • FIG. 9B is an enlargement in the region between 0 and 0.6 seconds
  • FIG. 9C is an enlargement of the range between 28.4° C and 30.5° C.
  • Samples 14 and 15 demonstrate improved thermal shielding beyond about 2 minutes.
  • FIG. 10A is a graph showing temperature profiles for Samples 14 and 15, the glass references.
  • the insets of FIG. 10A shows the sample areas on the surface of Samples 14 (left inset) and Sample 15 (right inset).
  • the notation SX.Y denotes Sample number X at sampling location Y
  • the notation GZ denotes glass sample number Z.
  • FIG. 10B and IOC are enlargements of FIG. 10A.
  • FIG. 10B is an enlargement in the region between 0 and 0.1 seconds.
  • FIG. IOC is an enlargement of the region between about 42° C and about 50° C.
  • comparison of FIGs. 10A and IOC demonstrate that, on average, Sample 14 had a lower equilibrium temperature relative to Sample 15. It is noted that the reflectance spectra of Samples 14 and 15 were relatively anisotropic with respect to measurement location on sample surface (not shown). While it is not definitively known, it is believed that the variation of the temperature profiles with sampling location is due at least in part to variations in the ambient temperature of the room.
  • the sample was allowed to cool for about 35 min to about 1 hour before a subsequent profile was generated.
  • the ambient temperature of the room had changed and, therefore, for each temperature profile, the ambient room temperature was slightly different, as demonstrated in FIG. 10B.
  • FIGs. 11A and 11B are graphs showing plots of the time versus sampie/ giass and time versus AT samp ie/ATgi ass , respectively, for the samples and generated from the temperature profiles in FIG. 9A.
  • FIGs. 12A and 12B are analogous to FIGs. 11A and 11B and were generated from the temperature profiles in FIG. 10A. Referring to FIGS. 11(B) and 12(B) demonstrate that Samples 14 and 15 had a thermal shielding effect of about 20% and about 10% respectively, relative to the bare glass samples.
  • Example 4 - Additional Demonstrations of Optical Performance of One- Dimensional Photonic Crystals
  • This Example demonstrates the performance of one-dimensional photonic crystals including at least one fiuoropolymer-based dielectric layer in the repeating layers.
  • Samples 16 - 18 consisted of 1 - 3 repeat units, respectively, with each repeat unit consisting of a fluorinated polymer layer and a non-fluorinate polymer layer.
  • the non- fluorinated polymer was Hyflon® AD60 and the non- fluorinated polymer was polystyrene.
  • the fluorinated polymer precursor solution consisted comprised 220 of 10%> wt./vol. fluorinated polymer composition.
  • the non- fluorinated polymer solution consisted of 150 of a 10%) wt./vol. polystyrene in toluene.
  • the fluorinated polymer precursor solution was spin coated for about 2 minutes at 1200 rpm and the non- fluorinated polymer precursor solution was spin coated for about 2 minutes at 6000 rpm.
  • the deposited layers were plasma treated without curing. Plasma treatment was performed using an oxygen plasma at about 0.5 mbar and having a power density of about 5 W/L. Oxygen was flowed into the plasma chamber at a rate of about 65 seem. The deposited layers were plasma treated for about 5 seconds. The samples were allowed to rest in the plasma chamber for about 60 seconds prior to plasma treatment. Samples 16 - 18 had average thicknesses of about 1030 nm, 1700 nm, and 1740 nm, respectively.
  • FIGs. 13(A) and (B), 14(A) and (B), and 15(A) and (B) are the reflectance spectra obtained from Samples 16 - 18, respectively.
  • the inset of FIG. 13(B) shows the sampling locations (A - E) on the sample surfaces.
  • FIGs. 13(A) - 15(B) demonstrate that the photonic crystals have significant reflectivity with a band gap in the near-IR.
  • FIGs. 13(A) to 14(B) demonstrate a relatively small spectral shift with respect to the sampling location on the sample surface.
  • This example demonstrates the effect of precursor solution concentration and spin-coating parameters on the average thickness of one-dimensional photonic crystal dielectric layers.
  • AD60 fluoropolymer
  • the precursor solutions consisted of about 7.5% wt./vol. to about 20% wt./vol. of the fluoropolymer.
  • 100 mL to about 200 mL of each precursor solution was spin coated onto a glass substrate using a spin time of about 2 minutes.
  • TABLE 2 shows the formation parameters of each of the samples.
  • each sample was measured by reflectance spectroscopy as describe above. Thickness measurements were taken along various points (A - E) along the sample surface as shown in the inset of FIG. 13(B), and the results were averaged to obtain a final average layer thickness. The thicknesses at the various sampling points varied no more than about 3%..
  • FIGs. 16(A) and 16(B) are reflectance spectra obtained from points A - E of Samples 21 and 24, respectively.
  • the grouping of the reflectance spectra of FIG. 16(A) is representative of the grouping of reflectance spectra of Samples 19 - 22 (spin speed ⁇ 7200 rpm) and the group of the reflectance spectra of FIG. 16(B) is representative of the grouping of reflectance spectra of Samples 23 - 27 (spin speed > 7200 rpm).
  • 16(A) and 16(B) demonstrate that the reflectance spectra of the samples prepared with a spin speed of 7200 rpm or greater were more isotropic with the respect to the surface of the sample, relative to the reflectance spectra of samples prepared with a spin speed of less than 7200 rpm.
  • the aforementioned results suggests that the samples prepared with a spin speed of 7200 rpm or greater had more uniform thickness relative to samples prepared with a spin speed of less than 7200 rpm.
  • This Example further demonstrates the effect of plasma treatment on the reflectance spectra of one-dimensional photonic crystals.
  • Example 38 - 46 9 additional samples were formed (Samples 38 - 46) as fluoropolymer monolayers.
  • the fluorinated polymer precursor solution consisted of 10% wt./vol. or 20% wt./vol. of Hyflon® 60 AD.
  • the monolayers were formed by spin-coating 150 or 220 of the precursor solution at 12000 rpm.
  • the deposited monolayers were treated with an oxygen plasma having a power density of about 2.5 W/L - about 10 W/L for between 5 seconds and 1 minute.
  • the oxygen plasma was flowed into the plasma chamber at a rate of about 65 seem.
  • the monolayer thickness was measured before plasma treatment and after plasma treatment, using reflectance spectroscopy as described above and at various points on the sample surface (inset of FIG. 14(B) (A - E)). TABLE 3 displays the results of the thickness measurements. TABLE 3
  • a one dimensional photonic crystal comprising: a first dielectric layer having a refractive index 3 ⁇ 4 and comprising a fluoropolymer; a second dielectric layer having a refractive index n 2 ⁇ 3 ⁇ 4 and comprising a second polymer composition.
  • the fluoropolymer is a polymer comprising an alicyclic structure in the polymer main chain or an elastomer comprising a fluoropolyether chain.
  • the inventive concept 1 or 2 wherein the photonic crystal has a thermal shielding of between about 5% to about 75% when irradiated with light having a power of about 150 W, a colour temperature of about 3500 K and a spot size of about 4.75 mm, relative to a glass substrate having substantially the same dimensions.
  • the photonic crystal has a thermal shielding of at least about 20% when irradiated with light having a power of about 150 W, a colour temperature of about 3500 K and a spot size of about 4.75 mm, relative to a glass substrate having substantially the same dimensions.
  • any of the inventive concepts 1 to 4 wherein the one-dimensional photonic crystal comprises a plurality of first dielectric layers and a plurality of second dielectric layers, wherein the first dielectric layers and second dielectric layers are alternately stacked. 6. Any of the inventive concepts 1 to 5, wherein the one-dimensional photonic crystals comprises from 5 to 100 first dielectric layers and from about 5 to 100 second dielectric layers. 7. Any of the inventive concepts 1 to 6, wherein the one-dimensional photonic crystal comprises from 5 to 50 first dielectric layers and from about 5 to 50 second dielectric layers.
  • Any of the inventive concepts 8 to 10, wherein the band gap is a first order band gap.
  • any of the inventive concepts 1 to 20, wherein 3 ⁇ 4 is from about 1.1 to about 1.6. 22. Any of the inventive concepts of 1 to 21, wherein
  • any of the inventive concepts 1 to 24, wherein the f uoropolymer is a polymer comprising an alicyclic structure in the polymer main chain and comprising recurring units represented by: (A) the fluorodioxoles of formula (I):
  • Ri , R 2 , R 3 and R 4 are independently selected from the group consisting of -F, a Ci-C 6 fluoroalkyl, optionally comprising one or more oxygen atoms, a Ci-C 6 fluoroalkoxy, optionally comprising one or more oxygen atoms;
  • R5 and R6, equal to or different from each other, are independently selected from the group consisting of -F, a Ci-C 6 fluoroalkyl, optionally comprising one or more oxygen atoms, a Ci-C 6 fluoroalkoxy, optionally comprising one or more oxygen atoms; or
  • any of the inventive concepts 1 to 24, wherein the fluoropolymer is an elastomer comprising a fluoropoly ether chain, obtained by the UV-curing of compositions comprising: at least one functional fluoropoly ether compound comprising a fluoropolyoxyalkylene chain (R f ) and having at least two unsaturated moieties; and at least one photoinitiator.
  • the functional fluoropolyether compound is selected from the group consisting of compounds of formula (IV):
  • R f represents a fluoropolyoxyalkylene chain comprising recurring units having general formula: -(CF 2 ) k -CFZ-0-, wherein k is an integer of from 0 to 3 and Z is a fluorine atom or a C1-C5 perfluoroalkyl group, optionally comprising one or more oxygen atom;
  • J and J' are independently a bond or a divalent bridging group
  • Ti and T 2 are selected from the group consisting of:
  • R H is H or a Ci-C 6 alkyl group
  • R A is selected from the group consisting of:
  • R B is a divalent group selected from the group consisting of C1-C10 aliphatic group, C5-C14 cyclo aliphatic group; C 6 -Ci4 aromatic or alkylaromatic group.
  • any of the inventive concepts 1 to 28, wherein the second dielectric layer comprises poly(methyl methacrylate), polycarbonate, polystyrene, cellulose acetate, poly( vinyl carbazole), or any combination thereof.
  • a method of making a one-dimensional photonic crystal comprising:
  • a first layer on a substrate comprising spin-coating a first precursor solution onto the substrate, wherein the first precursor solution comprises a solvent and from about 0.1% weight by volume to about 50% weight by volume of a fluoropolymer and wherein the substrate is spun at a speed of about 1000 rpm to about 20000 rpm.
  • the inventive concept 30 or 31 wherein the substrate is spun at a speed from about 1000 rpm to about 15000 rpm. 33. Any of the inventive concepts 30 to 32, wherein the substrate is spun for at least 5 minutes. 34. Any of the inventive concepts 30 to 32, wherein the substrate is spun from about 5 seconds to about 5 minutes.
  • mbar millibar
  • Any of the inventive concepts 30 to 41 further comprising heating the spin-coated first precursor solution by heating to remove solvent.
  • the substrate comprises a second layer and wherein the first precursor solution is deposited on the second layer.
  • the second layer comprises a polymer composition distinct from the fluoropolymer composition.
  • the second layer comprises poly(methyl methacrylate), polycarbonate, polystyrene, cellulose acetate, poly(vinyl carbazole), or any combination thereof.
  • any of the inventive concepts 30 to 46, wherein the fluoropolymer is a polymer comprising an alicyclic structure in the polymer main chain and comprising recurring units represented by::
  • Ri , R 2 , R 3 and R 4 are independently selected from the group consisting of -F, a Ci-C 6 fluoroalkyl, optionally comprising one or more oxygen atoms, a Ci-C 6 fluoroalkoxy, optionally comprising one or more oxygen atoms;
  • R5 and R 6 are independently selected from the group consisting of -F, a Ci-C 6 fluoroalkyl, optionally comprising one or more oxygen atoms, a Ci-C 6 fluoroalkoxy, optionally comprising one or more oxygen atoms; or
  • any of the inventive concepts 30 to 46, wherein the fluoropolymer is an elastomer comprising a fluoropolyether chain, obtained by the UV-curing of compositions comprising: at least one functional fluoropolyether compound comprising a fluoropolyoxyalkylene chain (R f ) and having at least two unsaturated moieties; and at least one photoinitiator.
  • the functional fluoropolyether compound is selected from the group consisting of compounds of formula (IV):
  • R f represents a fluoropolyoxyalkylene chain comprising recurring units having general formula: -(CF 2 ) k -CFZ-0-, wherein k is an integer of from 0 to 3 and Z is a fluorine atom or a C1-C5 perfluoroalkyl group, optionally comprising one or more oxygen atom;
  • J and J' are independently a bond or a divalent bridging group
  • Ti and T 2 are selected from the group consisting of:
  • R H is H or a Ci-C 6 alkyl group
  • R A is selected from the group consisting of:
  • R is a divalent group selected from the group consisting of Ci-Cio aliphatic group, C5-C14 cycloaliphatic group; C 6 -Ci4 aromatic or alkylaromatic group.
  • any of the inventive concepts 30 to 50, wherein the thickness of the first layer does not vary by more than about 20%.
  • the inventive concept 51 wherein the thickness of the first layer does not vary by more than about 10%.
  • the inventive concept 52 wherein the thickness of the first layer does not vary by more than about 5%.
  • the first precursor solution comprises 0.1 % weight by volume to about 20% weight by volume of the fluoropolymer.
  • the photonic crystal is the photonic crystal of any of the inventive concepts 1 to 29 and wherein the first layer is the first dielectric layer.

Abstract

One-dimensional planar photonic crystals having at least one dielectric layer comprising a fluoropolymer are described. The photonic crystals generally include repeating layers having alternating dielectric layers, where ate least one of the dielectric layers includes a fluorinate polymer. The photonic crystals can have relatively few repeating layers while maintaining desirable reflectance. The photonic crystals can be formed with specifically adapted spin-coating techniques to promote uniformity of the thicknesses of the dielectric layers. In some embodiments, the dielectric layers can be plasma treated to improve the structural integrity of the photonic crystal as well as to promote a more homogenous interface between dielectric layers. The one-dimensional photonic crystals can also provide desirable amounts of thermal shielding in the near infrared.

Description

ONE-DIMENSIONAL PLANAR PHOTONIC CRYSTALS INCLUDING FLUOROPOLYMER COMPOSITIONS AND CORRESPONDING FABRICATION METHODS
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority to European patent application No. 14196624.2, filed December 5, 2014, the whole content of this application being incorporated herein by reference for all purposes.
TECHNICAL FIELD
The present invention relates to one-dimensional planar photonic crystals. More specifically, the present invention relates to one-dimensional photonic crystals including a fluoropolymer composition.
BACKGROUND
One-dimensional photonic crystals, owing to their potential technological applications, have a significant interest in the fields of optics and photovoltaics. One-dimensional planar photonic crystals have been investigated for use in a variety of applications including, but not limited to, optical filters, waveguides, very low threshold lasers, and photovoltaic devices (e.g., crystalline silicon photovoltaic cells, polymeric bulk heterojunctions, fluorescent concentrators, dye-sensitized solar cells). One-dimensional photonic crystals have a periodic dielectric layer structure. In general, the photonic crystals are constructed by sequentially forming dielectric layers with distinct compositions to form the periodic structure of the crystal. Correspondingly, the number of layers required to achieve a desirable reflectivity can significantly affect manufacturing time and costs. For example, an increased number of layers can lead to an increased probability of manufacturing errors or increased manufacturing costs. Furthermore, an increased number of layers can also lead to an increased probability of performance failure. SUMMARY
In a first aspect, the invention relates to a one-dimensional photonic crystal including a first dielectric layer having a refractive index ¾ and comprising a fluoropolymer. The one-dimensional photonic crystal further includes a second dielectric layer having a refractive index n2 ≠ ¾ and comprising a second polymer composition. In some embodiments, the fluoropolymer is a polymer including an alicyclic structure in the polymer main chain or an elastomer comprising a fluoropolyether chain. In some embodiments, the one-dimensional photonic crystal has a thermal shielding of between about 5% to about 75% when irradiated with light having a power of about 150 W, a colour temperature of about 3500 K and a spot size of about 4.75 mm, relative to a glass substrate having substantially the same dimensions.
In some embodiments, the one-dimensional photonic crystal includes a plurality of first dielectric layers and a plurality of second dielectric layers, with the first dielectric layers and second dielectric layers are alternately stacked and where the one-dimensional photonic crystals includes from 5 to 100 first dielectric layers and from about 5 to 100 second dielectric layers. In some embodiments, the one-dimensional photonic crystal has a band gap from about 300 nm to about 3000 nm. In some embodiments, the first dielectric layer has a thickness of from about 50 nm to about 5 μιη. In some embodiments, the photonic crystal has at least 10 repeat units, where 10 sequential repeat units have a reflectivity of at least 50% for a wavelength from about 300 nm to about 3000 nm, and where each of the 10 sequential repeat units comprises the first dielectric layer and the second dielectric layer in a stacked configuration. In some embodiments, ¾ is from about 1.1 to about 1.6.
In some embodiments, the fluoropolymer is a polymer having an alicyclic structure in the polymer main chain and including recurring units represented by:
(A) the fluorodioxoles of formula (I): R1 R 2
R3 R4
(I)
wherein Ri, R2, R3 and R4, equal to or different from each other, are independently selected from the group consisting of -F, a Ci-C6 fluoroalkyl, optionally comprising one or more oxygen atoms, a Ci-C6 fluoroalkoxy, optionally comprising one or more oxygen atoms;
(B) the fluorodioxolanes of formula (II):
R5 R6
V- -
/ \
CF2
(II)
wherein R5 and R6, equal to or different from each other, are independently selected from the group consisting of -F, a Ci-C6 fluoroalkyl, optionally comprising one or more oxygen atoms, a Ci-C6 fluoroalkoxy, optionally comprising one or more oxygen atoms; or
(C) the cyclopolymerizable monomers of formula (III):
CR7R8=CR9OCRioRii(CRi2Ri3)a(0)bCRi4=CRi5Ri6, (III) wherein each R7 to Ri6, independently of one another, is selected from -F, and a Ci-C3 fluoroalkyl, a is 0 or 1 , b is 0 or 1 with the proviso that b is 0 when a is 1.
In some embodiments, the fluoropolymers are the copolymers of tetrafluoroethylene and the fluorodioxoles of formula (I) having Ri=R3=R4 = -F and R2 = -OCF3 or wherein Ri=R2= -F and R3=R4= -CF3.
In some embodiments, the fluoropolymer is an elastomer comprising a fluoropoly ether chain, obtained by the UV-curing of compositions comprising: at least one functional fluoropolyether compound comprising a fluoropolyoxyalkylene chain (Rf) and having at least two unsaturated moieties; and at least one photoinitiator. In some embodiments, the functional fiuoropolyether compound is selected from the group consisting of compounds of formula (IV):
Ti-J-R J' -T2, (IV)
wherein
Rf represents a fluoropolyoxyalkylene chain comprising recurring units having general formula: -(CF2)k-CFZ-0-, wherein k is an integer of from 0 to 3 and Z is a fluorine atom or a C1-C5 perfiuoroalkyl group, optionally comprising one or more oxygen atom;
J and J' , equal to or different from each other, are independently a bond or a divalent bridging group, and
Ti and T2, equal to or different from each other, are selected from the group consisting of:
(A) -0-CO-CRH=CH2,
(B) -0-CO-NH-CO-CRH=CH2, and
(C) -0-CO-RA-CRH=CH2,
wherein RH is H or a Ci-C6 alkyl group; RA is selected from the group consisting of:
(j) -NH-RB-0-CO- (jj) -NH-RB-NHCOO-RB-OCO-;
wherein RB is a divalent group selected from the group consisting of C1-C10 aliphatic group, C5-C14 cyclo aliphatic group; C6-Ci4 aromatic or alkylaromatic group.
In some embodiments, the second dielectric layer comprises poly(methyl methacrylate), polycarbonate, polystyrene, cellulose acetate, poly(vinyl carbazole), or any combination thereof.
In some embodiments, the photonic crystal can be made by a method including forming a first layer on a substrate, the forming comprising spin- coating a first precursor solution onto the substrate, wherein the first precursor solution comprises a solvent and from about 0.1 % weight by volume to about 50% weight by volume of a fluoropolymer and wherein the substrate is spun at a speed of about 1000 rpm to about 20000 rpm. In some embodiments of the method, the substrate is spun at a speed from about 1000 rpm to about 15000 rpm. BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic depiction of a one-dimensional photonic crystal. FIG. 2 is a schematic depiction of sampling locations on a surface of a photonic crystal.
FIG. 3A is a graph showing reflectance spectra obtained from a photonic crystal having fluoropolymer and polystyrene dielectric layers and sampled at the locations schematically depicted in FIG. 2.
FIG. 3B is a graph showing reflectance spectra obtained from a photonic crystal having fluoropolymer and PVK dielectric layers and sampled at the locations schematically depicted in FIG. 2.
FIG. 4A is a graph showing P-polarized transmittance spectra obtained from the photonic crystal of FIG. 3A and sampled at the locations schematically depicted in FIG. 2.
FIG. 4B is a graph showing S-polarized transmittance spectra obtain from the photonic crystal of FIG. 3A and sampled at the locations schematically depicted in FIG. 2.
FIG. 4C is a graph showing P-polarized transmittance spectra obtained from the photonic crystal of FIG. 3B and sampled at the locations schematically depicted in FIG. 2.
FIG. 4D is a graph showing S-polarized transmittance spectra obtain from the photonic crystal of FIG. 3B and sampled at the locations schematically depicted in FIG. 2.
FIG. 5 is a graph showing reflectance spectra obtained from a photonic crystal having 3 repeat layers and sampled at the locations shown in the inset, the inset showing a schematic representation of sampling locations on the surface of the photonic crystal having 3 repeat layers.
FIG. 6 is a schematic representation of sampling location on the surface of a fluoropolymer monolayer fabricated by spin-coating at various speeds. FIG. 7A is a graph showing reflectance spectra obtained from a fluoropolymer monolayer fabricated by spin-coating at 1200 rpm and sampled at the locations schematically depicted in FIG. 6.
FIG. 7B is a graph showing reflectance spectra obtained from a fluoropolymer monolayer fabricated by spin-coating at 3600 rpm and sampled at the locations schematically depicted in FIG. 6.
FIG. 7C is a graph showing reflectance spectra obtained from a fluoropolymer monolayer fabricated by spin-coating at 4800 rpm and sampled at the locations schematically depicted in FIG. 6.
FIG. 8A is a schematic representation of a horizontal experimental set-up to obtain temperature profiles of photonic crystals.
FIG. 8B is a schematic representation of a vertical experimental set-up to obtain temperature profiles of photonic crystals.
FIG. 9A is a graph showing temperature profiles obtained from 2 glass samples, a photonic crystal having fluoropolymer and polystyrene dielectric layers, and a photonic crystal having fiuoropolymer and PVK dielectric layers, where the temperature profiles were obtained from the horizontal experimental set-up schematically depicted in FIG. 8A and where the inset is a schematic depiction of the sampling location on the surface of the photonic crystal.
FIG. 9B is an enlargement of FIG. 9A, showing the region between 0 and
0.6 minutes.
FIG. 9C is an enlargement of FIG. 9A, showing the region between 28.5° C and 30.5° C.
FIG. 10A is a graph showing the temperature profiles obtained from the glass samples and photonic crystals of FIG. 9A, where the temperature profiles were obtained from the vertical experimental set-up schematically depicted in FIG. 8B and wherein the inserts are schematic depictions of the sampling location on the surface of the photonic crystal having polystyrene dielectric layers (left inset) and of the photonic crystal having PVK dielectric layers (right inset).
FIG. 10B is an enlargement of FIG. 10A, showing the region between 0 and 0.1 minutes. FIG. IOC is an enlargement of FIG. 10A, showing the region between 42° C and 50° C.
FIG. 11 A is a graph showing plots of Tsampie/Tgiass generated from the temperature profiles displayed in FIG. 9A.
FIG. 11B is a graph displaying plots of ATsampie/ATgiass generated from the temperature profiles displayed in FIG. 9A.
FIG. 12A is a graph showing plots of Tsampie/Tgiass generated from the temperature profiles displayed in FIG. 10A.
FIG. 12B is a graph displaying plots of ATsampie/ATgiass generated from the temperature profiles displayed in FIG. 10A.
FIG. 13A is a graph displaying plots of reflectance spectra of a one- dimensional photonic crystal having one repeat unit over a wavelength range between about 200 and about 1070 nm.
Fig. 13B is a graph reflectance spectra of the one-dimensional photonic crystal of FIG. 13A over a wavelength range between about 960 nm and about 2500 nm.
FIG. 14A is a graph displaying reflectance spectra of a one-dimensional photonic crystal having two repeat units over a wavelength range between about 200 and about 1070 nm.
Fig. 14B is a graph displaying reflectance spectra of the one-dimensional photonic crystal of FIG. 14A over a wavelength range between about 960 nm and about 2500 nm.
FIG. 15A is a graph displaying reflectance spectra of a one-dimensional photonic crystal having three repeat units over a wavelength range between about 200 and about 1070 nm.
Fig. 15B is a graph displaying reflectance spectra of the one-dimensional photonic crystal of FIG. 15A over a wavelength range between about 960 nm and about 2500 nm.
FIG. 16A is a graph displaying reflectance spectra of a fluorinated polymer monolayer deposited using a spin speed of about 4800 rpm.
FIG. 16B is a graph displaying reflectance spectra of a fluorinated polymer monolayer deposited using a spin speed of about 7200 rpm. DETAILED DESCRIPTION
One-dimensional planar photonic crystals, (hereinafter, "one-dimensional photonic crystal) having significantly increased reflectance efficiency can be formed from optical materials including a fluoropolymer composition. The one- dimensional photonic crystals described herein include an interface between different optical materials having different indexes of refraction, where at least one of the optical materials includes an amorphous fluoropolymer. The one- dimensional photonic crystals described herein have a periodic structure formed from alternating layers of optical materials in which at least one of the alternating layers includes an amorphous fluoropolymer. The relatively high dielectric contrast of the one-dimensional photonic crystals can provide desirable levels of reflectivity while incorporating a relative few number of dielectric layers. In some embodiments, the one-dimensional photonic crystals described herein are formed by sequential deposition of the optical materials. In some such embodiments, specifically adapted solution and post-deposition processing techniques can be used to promote desirable properties of the interfaces between the optical materials. Additionally, the one-dimensional photonic crystals described herein can provide desirable levels of thermal shielding to underlying substrates.
Photonic crystals involve optical structures having a periodic arrangement of optical materials having different refractive indexes. Correspondingly, the refractive index of a photonic crystal is spatially periodic. In some embodiments, the period can be comparable to that of the wavelength of visible light. In general, for photonic crystals, the optical materials are dielectric materials and, therefore, the optical materials are also referred to as dielectric materials when describing photonic crystals. The photonic crystals described herein are one-dimensional photonic crystals and, correspondingly, have a refractive index that is periodic in a single dimension. One-dimensional photonic crystals have a structure formed from repeating layers of dielectric layers, where the dielectric layers in the repeating layers have different refractive indexes. The differences in the refractive indexes of the alternating dielectric layers form a photonic band gap along a single dimension. Based at least in part on the band gap, photons of some frequencies are transmitted (modes) through the photonic crystals and some frequencies are reflected. The group of transmitted frequencies are referred to as allowed bands (to photon propagation) and the group of reflected frequencies is referred to as a photonic band gap (or forbidden bands).
The one-dimensional photonic crystals of interest herein have repeating units, each including at least two dielectric layers with different refractive indexes, where at least one of the dielectric layers in the repeating layers includes at least one fiuoropolymer. The periodic arrangement of the repeating layers (or repeating units) can be referred to as a "stacked configuration." FIG. 1 is a schematic depiction of one embodiment of a one-dimensional photonic crystal according the present description. Referring to FIG. 1, photonic crystal 100 includes periodic repeating layers 102 (for clarity, only a first repeating unit is labelled). Repeating layers 102 include first dielectric layers 104 and a second dielectric layers 106 with respective widths 108, 110. First dielectric layers 104, second dielectric layers 106 or both include a fiuoropolymer. First dielectric layers 104 and second dielectric layers 106 have respective indexes of refraction ni and n2, ¾≠ n2. A band gap is formed, in part, along the length "L" of photonic crystal 100 and in the direction represented by axis 112. Photons of allowed modes can be transmitted through photonic crystal 100 in a direction along axis 112. Photons having a frequency in the photonic band gap are reflected. In some embodiments, the one-dimensional photonic crystals can have repeating units including more than two dielectric layers. For example, one, some or all of the repeating can have 3, 4, 5, 6, 7, 8, 9, 10, 100 or more distinct dielectric layers. In some embodiments, the one-dimensional photonic crystals of interest herein can have at least 5 repeat units and no more than 200, 100, 90, 80, 70, or 50 repeat units. A person of ordinary skill in the art will recognize additional ranges of number of repeat units within the explicitly disclosed ranges are contemplated and within the scope of the present disclosure.
In some embodiments, the one-dimensional photonic crystals of interest herein can have a two or more sets of repeating units. In such embodiments, each repeating unit of each set includes at least two dielectric layers with different indexes of refraction. In at least one set, at least one of the dielectric layers in each repeating unit includes at least one fluoropolymer. For example, in one embodiment a first set of repeat units can include dielectric layers A and B and a second set of repeat units can include dielectric layers C and D, where composition A includes a fluoropolymer. In such an example, the one dimensional photonic crystal can be schematically represented as: (AB)N(CD)M, where N and M are the number of repeat units AB and CD, respectively. In some embodiments, there can be other layers between (AB)N and (CD)M. In some embodiments, the one-dimensional photonic crystals of interest here can have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 100 or more sets of repeat units. A person of ordinary skill will recognize additional ranges of number of sets of repeat units within the explicitly disclosed ranges are contemplated and within the scope of the present disclosure.
It has been surprisingly discovered that photonic crystals having repeat units including a dielectric layer having at least one fluoropolymer layer can have significantly improved efficiency, relative to corresponding photonic crystals having a non-fluorinate polymer layer. In general, photonic crystals having a larger number of repeat layers have a larger reflectivity, relative to corresponding photonic crystals have a smaller number of repeat layers. The photonic crystals described herein can have significantly improved dielectric contrast and, correspondingly, the same or improved reflectivity as a corresponding photonic crystals having non-fluorinated polymer compositions, while including a fewer number of repeat units. Put another way, the photonic crystals described herein can have increased reflectivity relative to corresponding photonic crystals having only non-fluorinated polymer compositions, while including the same number of repeat units. Furthermore, because of the increased dielectric contrast, the on-dimensional photonic crystals described herein have an increased photonic band gap, relative to corresponding one- dimensional photonic crystals free of the fluoropolymer.
In general, the optical devices described herein can be formed by depositing precursor solutions using conventional deposition techniques. The dielectric compositions can be formed as precursor solutions that are sequentially deposited to form alternating dielectric layers using conventional deposition techniques including, but not limited to, spin coating, spray coating, knife edge coating or other appropriate techniques. In some embodiments, the precursor solutions can be deposited using printing techniques including, but not limited to, screen printing, inkjet printing and like. Deposition approaches including printing techniques can facilitate patterning of the precursor solution, although patterning can also be performed using a spin coating, spray coating or knife edge coating technique in conjunction with masks having appropriate geometries. Notwithstanding the particular deposition technique, after deposition, removal of at least a portion of the solvent from the deposited precursor solution can stabilize the deposited optical material. In some embodiments, the deposited precursor solution can be heated to remove at least a portion of the solvent. The resulting cured layer is generally sufficiently stable for further processing including, but not limited to, deposition of another optical layer on top of or adjacent to the cured layer.
For the one dimensional photonic crystals of interest herein, it has been found that specifically adapted processing techniques can improve the reflective and structural properties of the photonic crystals. In particular, specifically adapted deposition techniques and specifically adapted surface treatment techniques can be integrated into the processing approach to provide for improved layer thickness uniformity and improved adhesion between the fluoropolymer layers and the non-fluoropolymer layers, respectively. While any conventional method can be used to deposit the dielectric materials, it has been found that specifically adapted spin coating approaches can aid in the formation of more uniform dielectric layers with a more narrow distribution of refractive indexes. Correspondingly, photonic crystals formed from the sequential deposition of dielectric materials by the specifically adapted spin coating techniques described herein can have a more uniform spatial reflectivity. Furthermore, in some embodiments, specifically adapted post deposition layer processing techniques can also be used to enhance the structural stability of the photonic crystal by enhancing the mechanical strength and optical uniformity of the interface between the dielectric layers. In particular, between the deposition of a first dielectric material to form a first dielectric layer, and the subsequent deposition of a second dielectric material, the first dielectric layer can be plasma treated to enhance the adhesion between the first dielectric layer and the subsequently deposited second dielectric material. Specifically adapted interlayer plasma processing as just described can also promote the optical performance of the photonic crystal by providing a more uniform interface between dielectric layers of different refractive indexes.
The one dimensional photonic crystals of interest herein can also have significantly improved thermal shielding for relatively thin photonic crystal structures. In particular, due at least in part to the high reflectance efficiencies of the one-dimensional photonic crystals described herein, relative thin photonic crystals can provide a significant degree of thermal shielding to an underlying substrate. In such embodiments, the one dimensional photonic crystals can reflect near-IR radiation that would otherwise be absorbed by the underlying substrate. For example, many electronic devices, including but not limited to mobile devices (e.g. mobile phones, tablets, laptops, watches etc.) are used outdoors. These devices can absorb solar radiation and heat-up. The one- dimensional photonic crystals described herein can reflect some or all of the near-IR portion of the incident solar radiation away from the devices to keep them at lower temperature. Reduced operating temperatures can help prevent damage to the electronic device and can help improve performance. Similar benefits to thermal shielding can be attained in photovoltaic (PV) modules, where higher temperatures lead to the reduction of the conversion efficiency, especially in the case of silicon based PV modules. In some embodiments, the one-dimensional photonic crystals described herein can have from about 1 repeat unit to about 50 repeat units, from about 1 repeat unit to about 20 repeat units or from about 1 repeat unit to about 10 repeat units and can have a thermal shielding of from about 5% to about 95%, from about 5% to about 75%, from about 5% to about 50%, from about 5% to about 40% or from about 5% to about 30% thermal shielding in the near infrared spectrum (about 800 nm to about 3000 nm). In some embodiments, the one-dimensional photonic crystals described herein can have from about 1 repeat unit to about 50 repeat units, from about 1 repeat unit to about 20 repeat units or from about 1 repeat unit to about 10 repeat units and can have a thermal shielding of no less than about 5%, no less than about 10%, no less than about 20%, no less than about 40%> or no less than about 10% in the near infrared spectrum. Thermal shielding can be measured by irradiating a photonic crystal, at room temperature, with light having a power of about 150 W, a colour temperature of about 3500 K and a spot diameter of about 4.75 mm. The temperature of the photonic crystal can be monitored at an opposite surface (relative to the irradiated surface) to determine when the temperature of the photonic crystal is equilibrated. The same measurement can be repeated on a glass sample having substantially similar dimensions to the photonic crystal. The difference in equilibrated temperatures of the photonic crystal and glass substrate, relative to the equilibrated temperature of the glass substrate, can be multiplied by 100 and defined as the percent thermal shielding. A person of ordinary skill in the art will recognize that additional ranges of repeat units and thermal shielding percentages within the explicitly disclosed ranges are contemplated and within the scope of the present disclosure.
Photonic Crystals
The one-dimensional photonic crystals described herein include repeating units of dielectric layers, as explained above. The repeating units include at least a first dielectric layer having a fiuoropolymer and an adjacent second, distinct dielectric layer. In some embodiments, the second dielectric layer can include a (fluoro)polymer. The photonic bandgap of the photonic crystal can be specifically engineered by appropriate selection of the compositions and thicknesses of the dielectric layers.
The photonic band gap of the photonic crystal can be characterized by a central frequency and a width. In general, one-dimensional photonic crystals reflect wavelengths that are about twice the optical distance of the periodicity of the repeating layers. Correspondingly, for a repeating unit consisting of two dielectric layers, the thickness of the dielectric layers are selected to be about ¼ of the central frequency of the desired photonic bandgap, taking into account the refractive index. For example, in application settings where near IR reflection is desirable (e.g. , λο ~ 1000 nm), the dielectric layers can be selected to have a thickness of about λο/(4η) = 1000nm/(4n), where n is the refractive index of the dielectric layer and ο is the central frequency of the incident light. Layer thickness can be optically measured using techniques known in the art including, but not limited to, reflectance and transmittance spectroscopy, ellipsometry, profilometry and interference microscopy. With respect to transmittance spectroscopy, light incident on the top surface of a film is reflected by the top surface as well as the opposite bottom surface. The reflections and transmissions correspondingly produce interference patterns that give rise to fringes. Based upon the number of the fringes, the thickness of the dielectric layer can be determined according to the following formula:
t = where λι and λ2 are, respectively, the minimum and maximum incident wavelength, n is the index of refraction of the dielectric layer, N is the number of fringes in the interference pattern, Θ is the angle of incidence of the incoming light beam relative to the plane of the top surface of the dielectric layer, and t is the thickness of the dielectric layer. The average thickness of a dielectric layer can be determined by measuring the thickness of the dielectric layer at various points along the top surface of the layer and averaging the measurement results.
The composition of the dielectric layers can be selected to engineer the width of the photonic bandgap. In particular, the composition of the dielectric layer affects the indexes of the refraction of the layer and, correspondingly, affects the width of the photonic bandgap. For example, using a quarter wavelength model, the width of the photonic bandgap can be estimated by the following formula:
Figure imgf000015_0001
where Δ ο is the bandwidth, ο is the center wavelength and where ¾ and n2 are, respectively, the refractive indexes of the first and second dielectric layers. For photonic crystals of interest herein, the first dielectric layer can have a refractive index of greater than about 1 , or from about 1.1 to about 1.6, from about 1.1 to about 1.5, from about 1.2 to about 1.45, or from about 1.2 to about 1.4. In some embodiments, for polymer based second dielectric layers can have a refractive index of greater than about 1 , or from about 1.2 to about 1.9, from about 1.3 to about 1.7, from about 1.35 to about 1.7, or from about 1.4 to about 1.7. In some embodiments, inorganic based second dielectric layers can have an index of refractions that is greater than about 1.3, or from about 1.3 to about 7, from about 1.3 to about 5 or from about 1.4 to about 5. In some embodiments, the composition of the first and second dielectric layers can be selected such that |n2- ni | is at least about 0.001 , at least about 0.01 , at least about 0.1 , or at least about 0.2, or at least about 0.3, or at least about 0.4, or at least about 0.5, or at least about 0.6, or at least about 0.7, or between about 0.1 to about 1 , between about 0.1 to about 0.7, between about 0.1 to about 0.5, or between about 0.1 to about 0.4. In some embodiments, n2 > 1 and |n2-ni | can be within the aforementioned ranges. In some embodiments, the composition of the first and second dielectric layer is chosen such that n2 > ¾ and in other embodiments, is chosen such that ¾ > n2. In either of the aforementioned instances, the quantity |n2-ni | can be within the ranges described above. A person of ordinary skill in the art will recognize that additional ranges of indexes of refraction and |n2-ni | within the explicitly disclosed ranges are contemplated and within the scope of the present disclosure.
In some embodiments, the one-dimensional photonic crystals of interest herein can have a band gap from about 300 nm to about 3000 nm, from about 400 nm to about 2500 nm, from about 800 nm to about 2000 nm, from about 800 nm to about 1700 nm or from about 600 nm to about 1700 nm. In some embodiments, the one-dimensional photonic crystals of interest herein can have a first order band gap of from about from about 500 nm to about 3000 nm, from about 500 nm to about 2000 nm, or from about 800 nm to about 1700 nm. In some embodiments, the on-dimensional photonic crystals of interest herein can have a second order band gap from about 500 nm to about 2000 nm, from about 500 nm to about 1500 nm, from about 500 nm to about 1500 nm or from about 600 nm to about 1300 nm. In some embodiments, the width (full width half maximum ("FWHM")) of the first diffraction order band gap can be from about 50 nm to about 500 nm, from 100 nm to about 500 nm or from about 100 nm to about 400 nm or from about 100 nm to about 300 nm. Higher order band gaps (e.g. second order, third order, etc.) can have a FWHM within the same ranges as described for first diffraction order band gaps. A person of ordinary skill in the art will recognized additional ranges of band gaps and widths within the explicitly disclosed ranges are contemplated and within the scope of the present disclosure.
As described in detail above, it has been surprisingly found that the one- dimensional photonic crystals incorporating repeating units including at least one dielectric layer having a fluoropolymer composition have significantly improved efficiency with respect to reflectivity. In particular, relative to corresponding one-dimensional photonic crystals free of a dielectric layer with a fluoropolymer composition, the presently described photonic crystals can achieve the same or greater reflectivity with a smaller number of repeat units. In general, increasing the number of repeat units in a one dimension photonic crystal increases the amount the incident light reflected. For the ID photonic crystals described herein, the photonic crystals can have at least 1 repeat unit or at least 5 repeat units and no more than 200 repeat units, no more than 100 repeat units, no more than 50 repeat units, no more than 30 repeat units, no more than 20 repeat units, no more than 15 repeat units, no more than 13 repeat units, no more than 10 repeat units, no more than 9 repeat layers or no more than 7 repeat units. In some embodiments, the one-dimensional photonic crystals can have from 5 to 200 first dielectric layers and from 5 to 200 second dielectric layers; from 5 to 100 first dielectric layers and from 5 to 100 second dielectric layer; from 5 to 50; 5 to 30 first dielectric layers and 5 to 30 second dielectric layers; 5 to 15 first dielectric layers and 5 to 15 second dielectric layers; or 5 to 10 first dielectric layers and 5 to 10 second dielectric layers; where the dielectric layers are in an alternating stacked configuration. In such embodiments, the one-dimensional photonic crystals of interest herein have a reflectivity of at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% or at least 98%, for a wavelength from about 300 nm to about 3000 nm, from about 400 nm to about 2500 nm, from about 800 nm to about 2000 nm, form about 800 nm to about 1700 nm or from about 600 nm to about 1700 nm. In some embodiments, the one-dimensional photonic crystals of interest herein can have at least 10 repeat units where 10 sequential repeat units have a reflectivity of at least 70%, at least 80%, at least 90%, at least 92% or at least 95%, for a wavelength between about 800 nm to about 1700 nm. A person of ordinary skill in the art will recognize additional ranges of repeat layers, reflectivity and band gaps within the explicitly disclosed ranges are contemplated and within the scope of the present disclosure.
The thickness of the dielectric layers can be selected to engineer a desired band gap, with respect to the dielectric constant of the dielectric layers. Based upon the present disclosure, a person of ordinary skill in the art will know how to select appropriate dielectric layer thicknesses based on the intended application setting of the one-dimensional photonic crystal (e.g., based upon the desired band gap for the application setting). In some embodiments, the first dielectric layer or second dielectric layer can have a thickness (e.g. 108, 1 10 of FIG. 1) of from about 50 nm to about 5 μιη, from about 50 nm to about 2 μιη, from about 100 nm to about 2 μιη, from about 200 nm to about 2 μιη or from about 200 nm to about 1 μιη. A person of ordinary skill in the art will recognize additional thickness ranges within the explicitly disclosed ranges are contemplate and within the scope of the present disclosure.
Dielectric Layer Compositions
The one-dimensional photonic crystals of interest herein include repeating layers including at least a first dielectric layer and an adjacent second dielectric layer. The first dielectric layer includes a first dielectric composition including a fluoropolymer, and has a bulk refractive index, ¾ . The first dielectric composition can optionally include other components that promote improved optical or mechanical properties or processing characteristics of the composition. The second dielectric layer includes a second dielectric composition and has a bulk refractive index n2≠ ¾ . The second dielectric layer includes an organic or nonorganic composition and can also include other components as described above. The first dielectric composition includes one or more fluoropolymers and, optionally, one or more additional components. As described in detail above, it has been surprising discovered that photonic crystals having repeat layers including a first dielectric layer having a first dielectric composition with one or more fluoropolymers can have significantly improved reflectance efficiency, relative to corresponding photonic crystals free of a fluoropolymer. As used herein, fluoropolymers include polymers having a recurring unit that includes at least one fluorine atom.
A first class of fluoropolymers appropriate for use in the first dielectric layer includes amorphous fluoropolymers having alicyclic structures in the polymer main chain. As used herein, amorphous fluoropolymers refer to fluoropolymers that are substantially free of any internal crystal structure and, in particular, have a heat of fusion lower than 5 J/g as determined by differential scanning calorimetry ("DSC") according to ASTM D3418-08. Examples of amorphous fluoropolymers having alicyclic structures in the polymer main chain are described in, EP 803557 A to Avataneo et al., filed October 19, 2012, describing amorphous fluoropolymers having recurring units derived from at least one fluorinated monomer having alicylcic structres in the polymer main chain, recurring units derived form at least one fluorinated monomer having an - S02X functional group and, optionally, recurring units derived from at least one ethylenically unsaturated fluorinated monomer; EP 1256591 A to Tortelli et al., filed April 25, 2002, describing amorphous fluoropolymers in including perfluorinated polymers; EP 645406 A to Squire, filed May 31 , 1988, describing amorphous copolymers of perfluoro-2,2-dimethyl-l,3-dioxole; and EP 303298 A to Nakamura et al., filed December 8, 1988, describing fluorine-containing cyclic polymers, all of which are incorporated herein by reference.
In some embodiments, the amorphous fluoropolymer including alicyclic structures in the polymer main chain can have recurring units derived from at least one fluorinated monomer selected from the group consisting of:
- the fluorodioxoles of formula (I): R1 R 2.
Cv
(I)
wherein Ri, R2, R3 and R4, equal to or different from each other, are independently selected from the group consisting of -F, a Ci-C6 fluoroalkyl, optionally including one or more oxygen atoms, a Ci- C6 fluoroalkoxy, optionally including one or more oxygen atoms; the fluorodioxo lanes of formula (II):
R5 R6
CF2 (II)
wherein R5 and R6, equal to or different from each other, are independently selected from the group consisting of -F, a Ci-C6 fluoroalkyl, optionally including one or more oxygen atoms, a Ci- C6 fluoroalkoxy, optionally including one or more oxygen atoms; and
- the cyclopolymerizable monomers of formula (III):
Figure imgf000020_0001
wherein each R7 to Ri6, independently of one another, is selected from -F, and a Ci-C3 fluoroalkyl, a is 0 or 1 , b is 0 or 1 with the proviso that b is 0 when a is 1.
In some embodiments, the fluoropolymers including alicyclic structures in the polymer main chain suitable for the first dielectric component are those selected from the group consisting of:
- the copolymers of tetrafluoroethylene and the fluorodioxoles of formula (I) as defined above wherein Ri, R2, R3 and R4, equal to or different from each other, are independently selected from the group consisting of -F, a Ci-C6 fiuoroalkyl, optionally including one or more oxygen atoms, a Ci-C6 fluoroalkoxy, optionally including one or more oxygen atoms; preferably wherein Ri, R2, R3 and R4, equal to or different from each other, are independently selected from the group consisting of -F, a C1-C3 perfluoroalkyl, e.g. -CF3, -C2F5, - C3F7, and a Ci-C3 perfiuoroalkoxy optionally including one oxygen atom, e.g. -OCF3, -OC2F5, -OC3F7, -OCF2CF2OCF3; more preferably wherein Ri=R2= -F and R3=R4 is a Ci-C3 perfluoroalkyl, preferably R3=R4= -CF3 or wherein Ri=R3=R4 = -F and R2 is a Ci-C3 perfiuoroalkoxy, e.g. -OCF3, -OC2F5, -OC3F7; and
- the polymers including recurring units derived from the cyclopolymerizable monomers of formula (III) as defined above, wherein each R7 to Ri6, independently of one another, is selected from -F, and a Ci-C3 fiuoroalkyl, a is 0 or 1, b is 0 or 1 with the proviso that b is 0 when a is 1 ; preferably in formula (III) each R7 to Ri6 is -F; more preferably in formula (III) each R7 to Ri6 is -F, a=l and b=0.
In some embodiments, the fluoropolymers including alicyclic structures in the polymer main chain for the first dielectric component are those selected from the group consisting of:
- the copolymers of tetrafluoroethylene and the fiuorodioxoles of formula (I) as defined above wherein Ri=R3=R4 = -F and R2 = - OCF3 or wherein Ri=R2= -F and R3=R4= -CF3 ; and
- the polymers including recurring units derived from the cyclopolymerizable monomers of formula (III) as defined above, wherein each R7 to Ri6 is -F, a=l and b=0.
In some embodiments, the fluoropolymers including alicyclic structures in the polymer main chain for the first dielectric component are those selected from the group consisting of: - the amorphous copolymers of tetrafluoroethylene and the fluorodioxoles of formula (I) as defined above wherein Ri=R3=R4 = -F and R2 = -OCF3 or wherein Ri=R2= -F and R3=R4= -CF3 ; and
- the amorphous polymers including recurring units derived from the cyclopolymerizable monomers of formula (III) as defined above, wherein each R7 to Ri6 is -F, a=l and b=0.
Amorphous fluoropolymers including recurring units derived from fluorodioxoles of formula (I) suitable for the photonic crystal of the invention are commercially available under the trade name HYFLON® AD (e.g. AD40 (nFP = 1.331) and AD60 (npp =1.327)) (Commercially available from Solvay Specialty Polymers Italy SpA) and TEFLON® AF (Commercially available from Du Pont), whereas amorphous fluoropolymers including recurring units derived from cyclopolymerizable monomers of formula (III) are commercially available under the trade name CYTOP® (Asahi Glass Company).
The amorphous fluoropolymers including recurring units derived from fluorodioxoles of formula (I) or from monomers of formula (III) and of interest herein can have a bulk refractive index npp of from about 1.250 to about 1.350 or from about 1.298 to about 1.334. A person of ordinary skill in the art will recognize additional ranges of bulk refractive indexes within the specifically disclosed ranges are contemplated and within the scope of the present description.
A second class of fluoropolymers suitable for use in the first dielectric layer include elastomers having fluoropolyether chains. In some embodiments, the elastomer can obtained by the UV-curing of compositions including: at least one functional fluoropolyether compound having a fluoropolyoxyalkylene chain (Rf) and having at least two unsaturated moieties; and at least one photoinitiator, as described in WO 2010/094661 to Koo et al , filed February 16, 2010, which is incorporated herein by reference.
The functional fluoropolyether compound can be selected among those compounds of formula (IV):
Tj-J-RfJ' -T2 (IV) - Rf represents a fluoropolyoxyalkylene chain including recurring units having general formula: -(CF2)k-CFZ-0-, wherein k is an integer of from 0 to 3 and Z is selected between a fluorine atom and a C1-C5 perfluoroalkyl group, optionally including one or more oxygen atom; preferably chain Rf complies with formula: - (CF20)p(CF2CF20)q(CFYO)r(CF2CFYO)s-(CF2(CF2)zCF20)t- wherein Y is a C1-C5 perfluoroalkyl group, optionally including one or more oxygen atom, z is 1 or 2; and p, q, r, s, t are integers > 0; chain Rf more preferably complies with formula: -(CF20)p- (CF2CF20)q. - wherein p ' and q' are integers > 0; said chain Rf typically has an average molecular weight of more than 1000 and less than 3500;
- J and J' , equal to or different from each other, are independently a bond or a divalent bridging group, and
- Ti and T2, equal to or different from each other, are selected from the group consisting of:
(A) -0-CO-CRH=CH2,
(B) -0-CO-NH-CO-CRH=CH2, and
(C) -0-CO-RA-CRH=CH2,
wherein RH is H or a Ci-C6 alkyl group; RA is selected from the group consisting of:
(j) -NH-RB-0-CO- and
(jj) -NH-RB-NHCOO-RB-OCO-,
wherein R is a divalent group selected from the group consisting of C1-C10 aliphatic group, C5-C14 cycloaliphatic group; C6-Ci4 aromatic or alkylaromatic group.
In formula (IV) chain Rf has preferably an average molecular weight between 1000 and 3000, more preferably between 1 100 and 3000, even more preferably between 1 100 and 2500; it is thus understood that in corresponding preferred structures as above detailed p, q, r, s, t, p ' and q' represent integers selected so as to comply with these molecular weight requirements. A person of ordinary skill in the art will recognize additional molecular weight ranges within the explicitly disclosed ranges are contemplated within the scope of the present disclosure.
In some embodiments, suitable compounds of formula (IV) can be selected from the group consisting of:
Figure imgf000024_0001
wherein in formulae (i) to (iv) p' and q' are selected so that the average molecular weight of chain Rf ls preferably comprised between 1000 and 3500. A person of ordinary skill in the art will recognized additional molecular weight ranges within the explicitly disclosed range are contemplated and within the scope of the present disclosure.
Compositions suitable for the preparation of elastomeric polymers by UV curing are commercially available from Solvay Specialty Polymers Italy SpA under the trade name Fluorolink®, e.g. Fluorolink® MD500 PFPE. In some embodiments, the elastomeric polymers obtainable by UV curing of a functional fluoropolyether compound of formula (IV) of interest herein have a bulk refractive index npp of from about 1.250 to about 1.350.
A third class of suitable fluoropolymers for use in the first dielectric component are fluoroelastomers. In general, fluoro elastomers are amorphous polymers and have a glass transition temperature ("Tg") below room temperature, in most cases even below 0° C. Suitable fluoroelastomers advantageously comprise recurring units derived from vinylidene fluoride and/or from tetrafiuoroethylene.
In some embodiments, the fluoroelastomer used as the first dielectric component in the photonic crystal of the invention consists of recurring units derived from vinylidene fluoride and/or from tetrafiuoroethylene and at least one other fluorinated monomer. In particular suitable fluorinated monomers can be selected from:
- fluoroalkylvinylethers of formula
Figure imgf000025_0001
wherein Rn is a Ci-C6 fluoroalkyl, e.g. "CF3, -C2F5, -C3F7;
- fluoro -oxyalkylvinylethers of formula
Figure imgf000025_0002
wherein X and XI are each independently selected from -H and -F and Ris is a C1-C12 perfluorooxyalkyl, containing one or more ether groups, for example perfluoro-2-propoxy-propyl; in particular compounds having general formula:
Figure imgf000025_0003
wherein R19 is selected from C2-C6 linear or branched fluoroalkyl, C5-C6 cyclic fluoroalkyl, C2-C6 linear or branched fluorooxyalkyl containing from one to three oxygen atoms, preferably selected from the following: CF2=CFOCF2OCF2CF3, CF2=CFOCF2OCF2CF2OCF3, CF2=CFOCF2OCF3.
The fluoroelastomer can optionally contain recurring units derived from C3-Cs fluoroolefins, optionally containing hydrogen atoms, chlorine and/or bromine and/or iodine, C2-C8 non- fluorinated olefins, preferably ethylene and/or propylene. In some embodiments, the fluoroelastomers of the first dielectric layer can include those described in U.S. 5,585,449 ('"449") to Arcella et al, filed December 22, 1994, describing fluoroelastomers including monomeric layers deriving form a bis-olefin; U.S. 5,264,509 to Arcella et al. , filed February 8, 1993, describing fiuroelastomers based on vinylidene fluoride; EP 683149 A to Arcella et al. , filed May 9, 1995, describing peroxide curable fluoroelastomers; and EP 1626068 A to Arrigoni et al., filed June 15, 2005, describing perfiuoroelastomer gels, all of which are incorporated herein by reference. In particular, the '449 patent describes that the fluoroelastomer can optionally contain from 0.01 to 1 mol% of recurring units derived from bis- olefins.
Non-limiting examples of suitable fluoroelastomers include, but are not limited to copolymers of vinylidene fluoride, hexafluoropropene, tetrafluoroethylene and perfluoroalkyl vinyl ethers; copolymers of vinylidene fluoride, hexafluoropropene and optionally tetrafluoroethylene; copolymers of vinylidene fluoride, perfluoroalkyl vinyl ether, and optionally tetrafluoroethylene; copolymers of vinylidene fluoride, C2-Cs non-fluorinated olefins, hexafluoropropylene and/or perfluoroalkyl vinyl ether and tetrafluoroethylene; copolymers including vinylidene fluoride and fluoromethoxyvinyl ether and optionally perfluoroalkyl vinyl ether and tetrafluoroethylene ; copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ether. For example, the fluoroelastomer can include, but is not limited to, poly(vinyldiene fluoride) (npvdf = 1.42) and poly(tetrafluoroethylene) (nptfe = 1.35).
In some embodiments, desirable fluoroelastomers for the first dielectric layer can be selected from the group consisting of: copolymers of vinylidene fluoride (55-85 mol%), hexafluoropropene (15-45 mol%) and optionally tetrafluoroethylene (0-30 mol%); copolymers of vinylidene fluoride (50-80 mol%), perfluoroalkyl vinyl ether (5-50 mol%), and optionally tetrafluoroethylene (0-20 mol%); copolymers of vinylidene fluoride (20-30 mol%), C2-Cs non-fluorinated olefins (10-30 mol%), hexafluoropropylene and/or perfluoroalkyl vinyl ether (18-27 mol%) and tetrafluoroethylene (10-30 mol%); copolymers including vinylidene fiuoride (50-80 mol%) and fluoromethoxyvinyl ether (20-50 mol%) and optionally tetrafluoroethylene (0-20 mol%); copolymers of tetrafluoroethylene (50-80 mol%) and perfluoroalkyl vinyl ether (20-50 mol%); copolymers of tetrafluoroethylene (50-80 mol%) and perfluoromethoxyvinyl ether (20-50 mol%); copolymers of tetrafluoroethylene (45-65 mol%), C2-Cs non-fluorinated olefins (10-40 mol%), perfluoroalkyl vinyl ether or vinylidene fluoride (0-40 mol%); copolymers of tetrafluoroethylene (33- 75 mol%), perfluoroalkyl vinyl ether (15-45 mol%) and vinylidene fluoride (10- 22 mol%).
Fluoroelastomers suitable for the photonic crystals described herein are commercially available under the trade name TECNOFLON® (Solvay Specialty Polymers Italy SpA), TECNOFLON® PFR (Solvay Specialty Polymers Italy SpA), VITON® (Du Pont), KALREZ® (Du Pont), DAIEL® (Daikin), FLUOREL® (Dyneon, 3M). The bulk refractive index npp of fluoroelastomers of interest herein is from about 1.320 to about 1.400.
A fourth class of suitable fluoropolymers for use in the first dielectric component are those selected from the group consisting of fluorosilicone rubbers ("FVMQ"), for example, those described in PIERCE, O.R., et al, "Fluorosilicone rubber," Industrial and Engineering Chemistry Research, 1960, vol.52, p.783-784 and in Cornelius, D.J., et al , "The unique properties of silicone and fluorosilicone elastomers," Polym. 1985, vol.25, p.467-473, both of which are incorporated by reference herein.
Fluorosilicone rubbers can include contain recurring units of formula (V):
-(Si(CH3)(RF)-0-)- (V)
where RF is a Ci-C6 fluoroalkyl, typically -CH2CH2CF3. Fluorosilicone rubbers suitable for the photonic crystals described herein are commercially available under the trade name Silastic® (Dow Corning), FQE® /FSE® (Momentive Performance Materials), FE® (Shin-Etsu), ELASTOSIL® FLR (Wacker).
In some embodiments, the fluoropolymer for the first dielectric layer is desirably selected from the groups consisting of the fluoropolymers including alicyclic structures in the polymer main chain and the elastomers including fluoropolyether chains as defined above. In such embodiments, it can also be desirable to select fluoropolymers having a bulk refractive index npp that is no more than about 1.350 or from about 1.250 to about 1.350. Applicant has surprising discovered that the selection of such fluoropolymers can allow for one-dimensional photonic crystals having significantly improved reflectance efficiency, as described above.
In some embodiments, the first dielectric composition can include one or more additional components, including but not limited to, viscosity modifiers, solvents, emulsifiers, organic and inorganic fluorophores, phosphorescence and chemiluminescent materials, non-linear optical materials, charge transport dopants, chemical receptors, and any combination thereof. In some embodiments, the first dielectric composition consists essentially of one or more fluoropolymers. When the first dielectric compositions includes more than one fluoropolymer and/or includes one or more additional components as described above, then the effective refractive index ¾ of the first dielectric component can be determined according to the suitable effective medium approximation as discussed in GHER, R.J., et al. Optical properties of nanostructured optical materials. Chem. Mater.. 1996, vol.8, p.1807-1819. In some embodiments, the total concentration of the one or more fluoropolymers in the first dielectric composition is from about 50 weight percent ("wt%") to about 99 wt%, from about 60 wt% to about 95 wt%, from about 70 wt% to about 95 wt%, or from about 80 wt% to about 95 wt%, relative to the total weight of the first dielectric composition. In some embodiments, the toatl concentration of the one or more fluoropolymers is at least 60 wt%, at least 70 wt%, at least 85 wt%, at least 90 wt%, at least 95 wt% or at least 97 wt%, relative to the total weight of the first dielectric composition. A person of ordinary skill in the art will recognize that additional concentration ranges within the explicitly disclosed ranges are contemplated and within the scope of the present disclosure.
The second dielectric layer composition can be an organic or an inorganic composition. In some embodiments, organic materials for the second dielectric layers described herein include, but are not limited to polymeric materials, in particular polymeric materials having a refractive index n2 - ¾ is at least 0.001. Non limiting examples of suitable polymeric materials include, for example, poly(methyl methacrylate) (nPMMA = 1.494), polycarbonate (nPC = 1.590), polystyrene (nPS = 1.597), poly(styrene-co-acrylonitrile) (nSAN = 1.572), poly(vinyl carbazole) (η Ρνκ = 1.683), cellulose acetate (ncA = 1.477), polysulfone (nps = 1.59), polyethylene (nPE = 1.49), poly( vinyl acetate) (npva=1.467), and poly(vinylchloride) = (npvc = 1.539). In some embodiments, the second dielectric layer includes an organic material selected from the group consisting of poly(methyl methacrylate), polycarbonate, polystyrene, cellulose acetate and poly(vinyl carbazole). Non-limiting examples of suitable inorganic materials include, but are not limited to, silica (η¾ο2 = 1.458), titania (nTio2 = 2.460), hafnia (nHf02 = 1.888), silicon (nSi = 3.497) and germanium (¾¾ = 4.545). Fabrication of Photonic Crystals
The one dimensional photonic crystals described herein can be fabricated by sequential deposition of precursor solutions, formed from the dielectric layer compositions, onto a substrate. In some embodiments, it has been found that specifically adapted solution processing techniques can promote the formation of dielectric layers having significantly improved optical performance. In some embodiments, specifically adapted plasma processing techniques can be used to increase the mechanical stability and optical performance of the photonic crystals described herein.
The composition of the substrate can be selected based on the desired application of the one dimensional photonic crystal. In some embodiments, the substrate can include, but is not limited to, silicon wafers, silica substrates, glass substrates, other inorganic material substrates, polymer substrates (e.g., organic polymer substrates), composites thereof and combinations thereof across a surface and/or in layers of the substrate. Polymer substrates or polymer coated substrates can be particularly desirable in application sections requiring flexibility and appropriate polymers can be selected with respect to processing temperatures. Appropriate polymers include, but are not limited to, polycarbonates, polyimides, polyesters, polyalkenes, copolymers thereof and mixtures thereof. For optical applications, it can be particularly desirable for the substrate to have a relatively flat surface. In some embodiments, the substrate can be an optical device, or a portion thereof, and the one-dimensional photonic crystal can be formed as an integrated component of the optical device. In other embodiments, the substrate can be a support upon which free-standing one- dimensional photonic crystal is fabricated. In such embodiments, the one dimensional photonic crystal can be separated from the substrate and, optionally, integrated into an optical device or other device with further processing.
In general, any suitable coating process can be used to deposit the precursor solution of the dielectric layer compositions onto a substrate. For example, the precursor solutions can be spin-coated, spray-coated, dip coated, knife edge coated or printed. Printing approaches include, but are not limited to, inkjet printing and screen printing. In general, notwithstanding the particular coating approach, the one dimensional photonic crystals are formed by sequentially depositing precursor solutions to sequentially form the first and second dielectric layers. Each dielectric layer can be formed by performing one or more spin-coating steps to achieve the desired thickness of the layer. As described below, after each spin-coating step, the deposited precursor solution can be thermally processed to stabilize the layer with respect to further processing including, but not limited to, deposition of the same or a different precursor solution.
In some embodiments, dielectric layers with significantly improved uniformity can be formed using specifically adapted spin-coating approaches. Spin-coating approaches involve placing a substrate on a rotating support, rotating the support at a selected frequency and depositing the precursor solutions at the location on the substrate surface corresponding to the axis of rotation. Such an approach is intended to promote complete coverage of the substrate with the precursor solution. For optical applications, relatively small variations in layer thickness can translate into large variations in optical properties (e.g. reflectivity) along the surface of the layers. Put another way, small variations in layer thickness can promote large anisotropy in the optical properties of a dielectric layer.
It has been discovered that specifically adapted spin coating approaches that can significantly improve the thickness uniformity of dielectric layers. In particular, for a selected layer thickness (as described above), the appropriate selection of spin frequencies, spin time and precursor solution viscosity can promote the formation of dielectric layers having significantly improved thickness uniformity. In some embodiments, the substrate can be spun at rates from about 100 revolutions per minute ("rpm") to about 20000 rpm, from about 200 rpm, to about 20000 rpm, from about 200 rpm to about 15000 rpm, from about 500 rpm to about 15000 rpm, from about 1000 rpm to about 10000 rpm, from about 2500 rpm to about 10000 rpm, from about 3000 rpm to about 9000 rpm, or from about 3000 rpm to about 7000 rpm. In some embodiments, the substrate can be spun for a duration from about 5 seconds to about 5 minutes, from about 10 seconds to about 4 minutes or from about 30 seconds to about 4 minutes. A person of ordinary skill in the art will know how to adjust the spinning speed and times within the disclosed ranges to obtain a desired layer thickness, based upon the present disclosure. In some embodiments, an initial low speed spin can be used to perform an initial bulk spreading of the precursor solution across the surface of the substrate. In such embodiments, the substrate can be spun at between 10 rpm to about 200 rpm and for about 10 seconds to about 1 minute. A person of ordinary skill in the art will recognized additional spin speeds and spin times within the explicitly disclosed ranges are contemplated and within the scope of the present disclosure. In some embodiments, the resulting films can have a thickness that varies no more than about 25%, no more than about 20%, no more than about 15%, no more than about 10%, no more than about 5% across the surface of the dielectric layer, relative to the average thickness of the dielectric layer.
In general the precursor solutions can be formed by creating a dispersion of the dielectric layer composition with one or more appropriate solvents. In general any suitable solvent or solvent blend including a plurality of solvents can be used. Suitable solvents include solvents that homogenous ly disperse the dielectric layer composition in the precursor solution, alone or in conjunction with a dispersant including, but not limited to a surfactant. In general, appropriate solvents homogenously disperse the dielectric layer composition so that it can be coated onto the substrate without an undesirable amount of settling/separation. With respect to dielectric layer compositions including polymers, desirable qualities of the dispersions can depend on the polymer concentration, the dielectric layer composition and the formation of the dispersion. The degree of dispersion can depend on the polymer-polymer and polymer- solvent interactions. For the first and second dielectric compositions described herein, suitable solvents can include, but are not limited to, water, organic solvents, such as alcohols and hydrocarbons, and combinations thereof. With respect to the fiuoropolymers described herein, suitable solvents can include, but are not limited to acetone, perfiuoropolyether fluids, hydrofluoroethers, or blends thereof. Desirable perfiuoropolyether ethers are commercially available as Galden® PFPE and Fomblin® PFPE from Solvay Specialty Polymers Italy SpA. Desirable hydrofluoroethers are commercially available as Novec™ Fluids from 3M Corporation and include compositions represented by the formula C2nFn+i-OCnH2n+i . In some embodiments, the selection of desirable solvent can involve the selection of solvents having a relative low boiling point. Solvents having a relative low boiling point can be removed from the deposited dielectric layer composition with relatively mild thermal processing. In some embodiments, the solvent can have a boiling point of less than about 250° C, less than about 150° C, less than about 100° C, or less than about 80° C, less than about 60° C or less than about 40° C. A person of ordinary skill in the art will recognize additional boiling point ranges within the explicitly disclosed ranges are contemplated and within the scope of the present disclosure.
In general, the concentration of the dielectric layer composition in the precursor solution can be selected to achieve desirable precursor solution viscosities for the spin-coating deposition as described above. In particular, the concentration of the dielectric layer composition in the precursor solution can be selected to achieve desirable viscosities for spin-coating deposition. In some embodiments, the concentration of the fluoropolymer in the precursor solution of the first dielectric composition can be between 0.01% to about 50%, from about 0.1%) to about 50%>, from about 0.5 to about 50%>, from about 0.1 to about 20%> from about 0.1 % to about 15%, or from about 0.1 % to about 10%> weight by volume ("wt./vol"). A person of ordinary skill in the art will recognize additional fluoropolymer concentrations within the explicitly disclosed ranges are contemplated within the scope of the present disclosure.
In some embodiments, after deposition of a dielectric layer composition, the deposited material can be thermally processed (e.g. cured) to remove solvent and stabilize the deposited material for subsequent processing. In some embodiments, the deposited material can be heated to remove solvent. Removal of the solvent can alter the layer thickness as well as the concentration of the dielectric composition components in the ultimately formed dielectric layer. The effects of solvent removal can be accounted for in the design of the precursor solution and/or spin-coating recipe. In particular, to account for removal of solvent, the initial concentration of the dielectric composition components in the precursor solution and the amount of precursor solution deposited on the substrate can be adjusted. Based upon the present disclosure, a person of ordinary skill in the art will know how to empirically determine the degree of adjustment. Subsequent to curing, the deposited dielectric composition can be further processed. Further processing can include, but is not limited to, deposition of another dielectric composition, distinct or the same as the cured dielectric composition, on the cured dielectric composition; plasma treatment of the cured dielectric layer or a combination of both.
In some embodiments, following curing, the dielectric layer can be plasma treated to improve the adhesion between polymeric based dielectric layers. Plasma treatment involves subjecting the cured dielectric layer to plasma at an appropriate power density in a plasma chamber. The plasma can clean the surface of a polymeric dielectric layer by, in part, removing organic contaminants at the surface. In some embodiments, the plasma can be a capacitatively coupled plasma ("CCP"). Relative to an inductively coupled plasma ("ICC"), CCPs can be less dense and result in more a more benign treatment of the dielectric layer. In general, the plasma can be formed by applying an electric field/electromagnetic field to a gas. In some embodiments, the gas can include or consist essentially of argon, oxygen, nitrogen or any combination thereof. The field can include a DC field (e.g. continuous filed) or an AC field, such as a periodic field (e.g., an RF field). The power of the resulting plasma can be at least partially determined by the amplitude of the voltage applied to the electrodes, as described further below. The plasma power and treatment time can be selected to help reduce undesirable damage to the dielectric layer. In some embodiments, a polymer based dielectric layer can be exposed to a plasma having a power density of from about 1 W/L to about 100 W/L, from about 1 W/L to about 50 W/L, from about 1 W/L to about 20 W/L or from about 1 W/L to about 10 W/L. In some embodiment, a polymer based dielectric layer can be exposed to a plasma for a duration from about 1 second to about 20 minutes, from about 1 second to about 10 minutes, from about 1 second to about 5 minutes, from about 30 seconds to about 5 minutes, from about 30 seconds to about 3 minutes, or from about 50 seconds to about 3 minutes. In some embodiments, the plasma treatment can be performed in a plasma chamber having a pressure of no more than about 100 millibar ("mbar"), no more than about 10 mbar, no more than about 5 mbar or no more than about 1 mbar. A person of ordinary skill in the art will recognize that additional ranges of power densities and exposure durations within the explicitly disclosed ranges are contemplated and within the scope of the present disclosure.
As used herein, power density refers to the average power of the plasma divided by the volume of the plasma chamber (e.g. vacuum chamber). The average power of the plasma can be defined as <P>=<Pon>*D, where <Pon> is the average input power supplied to the electrodes and D is the duty cycle. For continuous wave plasmas, D=l and
Figure imgf000034_0001
where <Pcw> is the average power of the continuous wave plasma.
EXAMPLES
The following Examples demonstrate the performance and fabrication of one-dimensional photonic crystals including at least one fluoropolymer-based dielectric layer in the repeating layers. In the Examples, one dimensional photonic crystals consisting of repeat layers consisted of a fluoropolymer based dielectric layer and a second polymeric based dielectric layer were formed. The fluoropolymer based dielectric layer consisted of a tetrafluoroethylene/2,2,4- trifluoro-5-trifluoromethoxy-l,3-dioxole copolymer (commercially available as HYFLON AD60 from Solvay Specialty Polymers Italy SpA) (nFP = 1.327). The second dielectric layer consisted of a non-fluorinated polymer that was either cellulose acetate (ncA = 1.477), poly(n-vinylcarbazole) ("PVK") (ηΡνκ = 1.683) or a polystyrene (nPS = 1.597). The cellulose acetate and PVK were commercially obtained from Sigma- Aldrich and ThermoFisher, respectively.
To fabricate the one-dimensional photonic crystals, precursor solutions of the fluoropolymer and non-fluorinated polymer were sequentially spin-coated to build the repeat layers. The fluoropolymer was dispersed in a perfluoropolyether solvent (Galden® PFPE HT110 commercially available from Solvay Specialty Polymers Italy SpA) to form a 2% wt./vol. - 10% wt./vol. solution of the fluoropolymer. The non-fluorinated polymer was dispersed in toluene to form a 2% wt./vol. - 10% wt./vol. solution of the non-fluorinated polymer. For each dielectric layer, the precursor solution was spin-cast and, subsequently, cured (by heating) to remove solvent and form the dielectric layer (unless explicitly stated otherwise). Spin coating was performed between 200 rpm and 12000 rpm and for about 2 minutes (unless explicitly stated otherwise). Prior to deposition of a subsequent precursor solution, the cured dielectric layer was subjected to plasma treatment to improve the adhesion between the dielectric layers of the ultimately formed one-dimensional photonic crystals.
Plasma treatment involved subjecting the cured dielectric layer to an air or oxygen plasma, at a power density of about 7.5 W/L for a duration of 10 seconds to 10 minutes. The gas was flowed into the plasma chamber at a flow rate of about 24 standard cubic centimetres per minute ("seem") to maintain a pressure of about 0.5 mbar. Following plasma treatment, the spin-coating deposition, curing, and plasma treatment of successive layers was repeated until the desired number of repeat layers (and repeat units) were formed.
Example 1 - Optical Performance of One-Dimensional Photonic Crystals
This Example demonstrates the performance of one-dimensional photonic crystals including at least one fluoropolymer-based dielectric layer in the repeating layers. To demonstrate performance, 2 samples were formed, each consisting of 9 repeat layers. The non-fluorinated polymer of samples 1 (Fig. 3A) and 2 (Fig. 3B) were, respectively, polystyrene and PVK. The dielectric layers of sample 1 had a thickness of about 347 nm for the fluoropolymer based dielectric layer and 187 nm for the non-fluorinated polymer based dielectric layer, respectively. The dielectric layers of samples 2 had a thickness of about 221 nm for the fluoropolymer based dielectric layer and 118 nm the non-fluorinated polymer based dielectric layer, respectively. The fluoropolymer precursor solutions were formed by adding a selected amount of polymer to an appropriate solvent. The fluorinated polymer precursor solutions were formed by adding 5g of Hyflon® AD60 to 100 ml of (Galden® HT 110). The polystyrene and PVK precursor solutions were formed by adding 7.5 g of polystyrene and 5g of PVK, respectively, to 100 ml of toluene. To form the fluorinated polymer dielectric layers, 130 μΙ_, of the corresponding precursor solution was deposited at the centre of the previous formed layer (or glass substrate for the first deposited layer) while spinning the glass substrate for about 2 minutes at 6000 rpm. For the polystyrene and PVK layers, 150 μΙ_, of the corresponding precursor solutions were spin-cast as just described but using a spin rate of about 9000 rpm. Subsequent to spin casting each PVK layer, the structure was cured on a hot plate at a temperature of about 80° C for about 2 minutes.
Plasmas treatment involved exposing the layers to an air plasma for 30 seconds with a power density of 7.5 W/L. The ultimately formed one- dimensional photonic crystals had a thickness of about 4.5 micrometers ("μιη") and about 3 μιη, for samples 1 and 2, respectively. Both samples had a length and width of about 2 cm. Sample 1 had a band gap of about 1500 nm and sample 2 had a band gap of about 1000 nm.
Optical performance was demonstrated by delivering light to the surface of the samples and measuring the reflectance and transmittance spectroscopy. Reflectance and transmittance spectra were obtained using optical fiber coupled AvaSpec ULS2048 spectrometers (200-1100 nm, resolution 1.4 nm) (commercially available from Avantes) and an ARCoptix FT-interferometer (900-2600 nm, resolution 8 cm"1). The light source was a combined deuterium- halogen light source Micropak DH-200-BAL (commercially available from Ocean Optics. Reflectance and transmittance spectra were obtained using spot sizes of about 2 nm and 0.5 mm to about 5 mm. The samples were mounted on a rotatable in order to perform variable incidence angle transmittance measurements. Reflectance spectra were taken at an angle of incidence of about 0°, relative to the plane defined by the sample surface, and at various points along the sample surface. FIG. 2 is a schematic depiction of the sampling points (each about 2 mm diameter) on the sample surface. Transmittance spectra were obtained for incidence angles of between about 0° and about 60°, relative to the plane defined by the sample surface. FIGS. 3A and 3B and 4A - 4D are graphs showing wavelength versus reflectance (reflectance spectrum) and wavelength versus transmittance (transmittance spectrum), respectively, obtained from samples 1 and 2.
Referring to FIGS. 3A and 3B, both samples had a reflectivity of about 85% or greater around the band gap. FIG. 3A is a graph showing a plots of incident wavelength vs. reflectance (reflectance spectrum) obtained from various locations about the surface of sample 1, as indicated in FIG. 2. FIG. 3 A demonstrates that around the band gap of about 1500 nm, the sample had a 1st order reflectance of at least about 85% and a second order reflectance of about 70% (at about 750 nm). Similarly, FIG. 3B is a graph showing the reflectance spectra from various location about the surface of sample 2, as indicated in FIG. 2. FIG. 3A demonstrates that around the band gap of about 1000 nm, sample 2 had a first order reflectance of about 98% and second order reflectance (at about 500 nm) of about 68%. It is noted that for sampling locations E (in the center of each sample), the reflectance spectra of samples 1 and 2 exhibited significant spectral shift with respect to the other locations due to a lower thickness uniformity there achieved being such point the solution deployment site.
Referring to FIGS. 4 A - 4D, both samples had monotonically decreasing transmittance with increased incident angles. FIG. 4A is a graph showing plots of wavelength vs. transmittance (transmittance spectrum) of P-polarized light obtained from sample 1 at various incidence angles. FIG. 4B is analogous to FIG. 4A and shows the transmittance spectra of S-polarized light. Referring to FIGS. 4A and 4B, in general, the transmittance monotonically decreased with increased incidence angle, for both P- and S-polarized light. However, the transmittance of the S-polarized components of the incident light was generally greater than that of the P-polarized light of the same wavelength. Similar results were obtained from the transmittance spectra of sample 2 as shown in FIGS. 4C and 4D, which are analogous to FIGS. 4A and 4B, respectively.
To demonstrate the effect of the number of repeat layers, a further sample (Sample 3) was formed consisting of 3 repeat layers. The non-fluorinated polymer of sample 3 was polystyrene The dielectric layers of sample 3 had an estimated average thickness of about 100 nm and 230 nm for the fluoropolymer based dielectric layer and the non-fluorinated polymer based dielectric layer, respectively. The thicknesses were estimated from thickness measurements made on similar samples (not shown). The dielectric layers were formed as described above in this Example using a spin speed of 4200 rpm for both the fluoropolymer and non- fluoropolymer dielectric layers. Similarly, plasma treatment was performed as described above with respect to the polystyrene layers. The ultimately formed one-dimensional photonic crystals had a thickness of about 1 micron and a length and width of about 2 cm. Following fabrication, reflectance spectra were obtained as described above. The reflectance spectra were obtained at various points along the surface of Sample 3, as indicated in the inset of FIG. 5.
Sample 3 showed a significant amount of reflectance for only 3 repeat layers. FIG. 5 is a graph showing the reflectance spectra obtained from Sample 3. Referring to FIG. 5, the spectra show a significant second order reflectance (at about 1100 nm) of about 23% to about 37% and a fourth order reflectance (at about 380 nm) of from about 35% to about 43%. As explained above, the significant variation in the reflectance spectrum obtained at point H (center of the sample) likely reflects that Sample 3 is thicker in the central region relative to peripheral regions A - E. Example 2 - Effect of Fabrication Parameters on the Thickness of One- Dimensional Photonic Crystals
This example demonstrates the effect of Spin-Coating parameters on the average thickness of one-dimensional photonic crystal dielectric layers.
To demonstrate the effect of fabrication parameters, 10 samples (Samples
4 - 13) were formed as described above. The samples were formed as monolayers and each sample consisted of a single dielectric layer formed from Hyflon® AD60 (fluoropolymer). The precursor solutions consisted of about 2% wt./vol. to about 7.5% wt./vol. of the fluoropolymer. To form the monolayers, 100 to about 200 μΐ, of each precursor solution was spin coated onto a glass substrate using spin rate of from about 1200 rpm to about 7200 rpm and a spin time of about 2 minutes. TABLE 1 shows the formation parameters of each of the samples.
TABLE 1
Sample No. Concentration Volume of Spin Speed Average of Precursor (rpm) Thickness of
Fluoropolymer Solution Monolayer in Precursor Deposited (nm)
Solution (ML)
(% wt./vol.)
4 2.5 100 7200 N/A
5 2.5 100 5400 N/A
6 2.5 100 3600 N/A
7 5 200 3600 170
8 5 200 2400 210
9 5 200 1200 280
10 7.5 200 4800 360
11 7.5 200 3600 370
12 7.5 200 2400 440
13 7.5 200 1200 680 Following formation of the monolayers, the thickness of each samples were measured by reflectance spectroscopy as describe above.. Thickness measurements were taken along various points along the sample surface as shown in FIG. 6, and the results were averaged to obtain a final average layer thickness. The thicknesses at the various sampling points varied no more than about 10% from the reported averages. For samples 4 - 6, the layer thicknesses were too small to allow for reliable thickness measurements via reflectance spectroscopy by interference (e.g. fringe) analysis.
Referring to TABLE 1 , samples prepared with increased spin speed and decreased fluoropolymer concentration had the smallest average thickness. For example, the average thickness of Samples 7 - 9 decreased from 280 nm to 170 nm when the spin speed was increased from 1200 rpm 3600 rpm. Similarly, the average thickness of Samples 10 - 13 decreased from 680 nm to about 360 nm when the spin speed was increased from 1200 rpm to 4800 rpm. Furthermore, comparison of the average thickness of Samples 7 - 9 with Samples 1 1 - 13, respectively, demonstrate that increasing the fluoropolymer concentration in the precursor solution increases the average thickness of the ultimately formed monolayer.
For the samples tested, in general, increasing spin speed resulted in monolayers having a more uniform thickness and, therefore, significantly uniform optical properties. FIGs. 7A - 7C graphs showing the reflectance spectra of samples 13, 1 1 and 10, respectively, taken at the various points along the sample surface as depicted in FIG. 6. Referring to FIG. 7A (spin speed = 1200 rpm), the reflectance spectrum of Sample 13, obtained at point G (center of the sample), is significantly different from the reflectance spectra obtained at points A - F. More particularly, the difference in the reflectance spectrum at point G appears to indicate that the monolayer of Sample 13 is thicker in the central region relative to the peripheral regions. Comparison of FIGs. 7B (spin speed = 3600 rpm) and 7C (spin speed = 4800 rpm) with 7A demonstrates that increasing the spin speed improves the uniformity of the reflectance spectra (and therefore uniformity in the thickness) of samples 1 1 and 10 across all sampling points and, therefore, results in more narrow distribution of reflectance spectra. With respect to Samples 11 and 10, FIGs. 7B and 7C, respectively, demonstrate that Sample 10 has a narrower distribution of reflectance spectra relative to Sample 11. Example 3 - Thermal Shielding
This Example demonstrates the thermal shielding by one-dimensional photonic crystals.
To demonstrate thermal shielding, samples 1 and 2 (renumbered as Samples 14 and 15 in this Example for consistency) were subjected to thermal shielding testing Thermal shielding was measured both horizontally and vertically, to facilitate thermal shielding measurements. In both instances, light having a power of about 150 W and a color temperature of about 3200 K (centre wavelength of about 900 nm) was delivered through a bundle of optical fibers and directed at the surface of the sample at a target location. A thermometer (Testo Mod.1 10 with a 6 mm diameter probe) was placed at the opposite surface and at a location corresponding to the target location. The thermal stability was evaluated by monitoring the temperature as a function of time while the incident light was directed at the target location. FIGS. 8A and 8B are schematic representations of the respective horizontal and vertical experimental set-ups. Referring to the FIGS. 8A and 8B, samples 902, 904 are supported on sample holder 906 and film 908 (grease film to improve adhesion of thermometer head to the substrate), respectively. Fiber optic bundles 910, 912 are displaced away from the surfaces of respective films 902, 904 at a respective distance of about 3 cm and 5 cm. Light exiting fiber optic bundles 910, 912 travels through respective samples 902, 904 to respective thermocouples 914, 916, which are in contact with respective samples 910, 912. The temperature of the samples 902, 912 is monitored by respective thermocouples 914, 916.
To perform the thermal shielding measurements, Samples 14 and 15 were illuminated for about 11 minutes (horizontal thermal stability) and 30 minutes (vertical thermal stability) while the temperature of the samples were monitored. For the horizontal thermal stability, measurements were taken at a single location along the samples. For the vertical thermal stability, the samples were moved in the plane of the sample between the thermocouple and optical bundle to obtain measurements at 3 locations along the samples. For reference, thermal stability measurements were also obtained for the bare glass substrate samples having dimensions that were substantially similar to those of Samples 14 and 15.
The tested samples had desirable thermal shielding, with Sample 14 having improved thermal shielding relative to Sample 15. FIG. 9A is a graph showing plots of time versus temperature ("temperature profile") obtained from horizontal thermal measurements of Samples 14 and 15 and the glass references. The inset of FIG. 9A is a schematic representation depicting the sampling area on surface of the samples. FIGS. 9B and 9C are enlargements of FIG. 9A. FIG. 9B is an enlargement in the region between 0 and 0.6 seconds and FIG. 9C is an enlargement of the range between 28.4° C and 30.5° C. Referring to FIGs. 9A - 9C, relative to the glass references, Samples 14 and 15 demonstrate improved thermal shielding beyond about 2 minutes. Moreover, Sample 14 reached thermal equilibrium at a much faster rate, relative to Sample 15 and the glass reference samples. In particular, referring to FIGS. 9A and 9C, thermal equilibrium was achieved for Sample 14 at about 3 seconds, while for Sample 15, thermal equilibrium was not reached after 11 minutes. Furthermore, FIGs 9A and 9C also demonstrate that Sample 14 had a lower equilibrium temperature relative to Sample 15. FIG. 10A is a graph showing temperature profiles for Samples 14 and 15, the glass references. The insets of FIG. 10A shows the sample areas on the surface of Samples 14 (left inset) and Sample 15 (right inset). In the figures, the notation SX.Y denotes Sample number X at sampling location Y and the notation GZ denotes glass sample number Z. FIGs. 10B and IOC are enlargements of FIG. 10A. FIG. 10B is an enlargement in the region between 0 and 0.1 seconds. FIG. IOC is an enlargement of the region between about 42° C and about 50° C. In general, comparison of FIGs. 10A and IOC demonstrate that, on average, Sample 14 had a lower equilibrium temperature relative to Sample 15. It is noted that the reflectance spectra of Samples 14 and 15 were relatively anisotropic with respect to measurement location on sample surface (not shown). While it is not definitively known, it is believed that the variation of the temperature profiles with sampling location is due at least in part to variations in the ambient temperature of the room. In particular, after each temperature profile was generated, the sample was allowed to cool for about 35 min to about 1 hour before a subsequent profile was generated. However, during that time, the ambient temperature of the room had changed and, therefore, for each temperature profile, the ambient room temperature was slightly different, as demonstrated in FIG. 10B.
FIGs. 11A and 11B are graphs showing plots of the time versus sampie/ giass and time versus ATsampie/ATgiass, respectively, for the samples and generated from the temperature profiles in FIG. 9A. FIGs. 12A and 12B are analogous to FIGs. 11A and 11B and were generated from the temperature profiles in FIG. 10A. Referring to FIGS. 11(B) and 12(B) demonstrate that Samples 14 and 15 had a thermal shielding effect of about 20% and about 10% respectively, relative to the bare glass samples. Example 4 - Additional Demonstrations of Optical Performance of One- Dimensional Photonic Crystals
This Example demonstrates the performance of one-dimensional photonic crystals including at least one fiuoropolymer-based dielectric layer in the repeating layers.
To demonstrate performance, 2 additional samples were formed (samples
16 - 18). Samples 16 - 18 consisted of 1 - 3 repeat units, respectively, with each repeat unit consisting of a fluorinated polymer layer and a non-fluorinate polymer layer. The non- fluorinated polymer was Hyflon® AD60 and the non- fluorinated polymer was polystyrene. The fluorinated polymer precursor solution consisted comprised 220 of 10%> wt./vol. fluorinated polymer composition. The non- fluorinated polymer solution consisted of 150 of a 10%) wt./vol. polystyrene in toluene. The fluorinated polymer precursor solution was spin coated for about 2 minutes at 1200 rpm and the non- fluorinated polymer precursor solution was spin coated for about 2 minutes at 6000 rpm. Following spin-coating of each layer, the deposited layers were plasma treated without curing. Plasma treatment was performed using an oxygen plasma at about 0.5 mbar and having a power density of about 5 W/L. Oxygen was flowed into the plasma chamber at a rate of about 65 seem. The deposited layers were plasma treated for about 5 seconds. The samples were allowed to rest in the plasma chamber for about 60 seconds prior to plasma treatment. Samples 16 - 18 had average thicknesses of about 1030 nm, 1700 nm, and 1740 nm, respectively. The reflectance spectra were obtained as described above. FIGs. 13(A) and (B), 14(A) and (B), and 15(A) and (B) are the reflectance spectra obtained from Samples 16 - 18, respectively. The inset of FIG. 13(B) shows the sampling locations (A - E) on the sample surfaces. FIGs. 13(A) - 15(B) demonstrate that the photonic crystals have significant reflectivity with a band gap in the near-IR. Furthermore, FIGs. 13(A) to 14(B) demonstrate a relatively small spectral shift with respect to the sampling location on the sample surface.
Example 5 - Additional Demonstrations of Effects of Fabrication Parameters on
Average Layer Thickness
This example demonstrates the effect of precursor solution concentration and spin-coating parameters on the average thickness of one-dimensional photonic crystal dielectric layers.
To demonstrate fabrication effects, 19 additional samples (Samples 19 -
37) were formed as described above. The samples were formed as monolayers and each sample consisted of a single dielectric layer formed from Hyflon®
AD60 (fluoropolymer). The precursor solutions consisted of about 7.5% wt./vol. to about 20% wt./vol. of the fluoropolymer. To form the monolayers, 100 mL to about 200 mL of each precursor solution was spin coated onto a glass substrate using a spin time of about 2 minutes. TABLE 2 shows the formation parameters of each of the samples. TABLE 1
Figure imgf000045_0001
Following formation of the monolayers, the thickness of each samples were measured by reflectance spectroscopy as describe above. Thickness measurements were taken along various points (A - E) along the sample surface as shown in the inset of FIG. 13(B), and the results were averaged to obtain a final average layer thickness. The thicknesses at the various sampling points varied no more than about 3%..
In general, samples prepared with a spin speed of 7200 rpm or greater had improved thickness uniformity relative to samples prepared with a spin speed of less than 7200 rpm. FIGs. 16(A) and 16(B) are reflectance spectra obtained from points A - E of Samples 21 and 24, respectively. The grouping of the reflectance spectra of FIG. 16(A) is representative of the grouping of reflectance spectra of Samples 19 - 22 (spin speed < 7200 rpm) and the group of the reflectance spectra of FIG. 16(B) is representative of the grouping of reflectance spectra of Samples 23 - 27 (spin speed > 7200 rpm). FIGs. 16(A) and 16(B) demonstrate that the reflectance spectra of the samples prepared with a spin speed of 7200 rpm or greater were more isotropic with the respect to the surface of the sample, relative to the reflectance spectra of samples prepared with a spin speed of less than 7200 rpm. The aforementioned results suggests that the samples prepared with a spin speed of 7200 rpm or greater had more uniform thickness relative to samples prepared with a spin speed of less than 7200 rpm.
Example 6 - Effect of Plasma Treatment on Reflectance
This Example further demonstrates the effect of plasma treatment on the reflectance spectra of one-dimensional photonic crystals.
To demonstrate the effect of plasma treatment, 9 additional samples were formed (Samples 38 - 46) as fluoropolymer monolayers. The fluorinated polymer precursor solution consisted of 10% wt./vol. or 20% wt./vol. of Hyflon® 60 AD. The monolayers were formed by spin-coating 150 or 220 of the precursor solution at 12000 rpm. The deposited monolayers were treated with an oxygen plasma having a power density of about 2.5 W/L - about 10 W/L for between 5 seconds and 1 minute. The oxygen plasma was flowed into the plasma chamber at a rate of about 65 seem. The monolayer thickness was measured before plasma treatment and after plasma treatment, using reflectance spectroscopy as described above and at various points on the sample surface (inset of FIG. 14(B) (A - E)). TABLE 3 displays the results of the thickness measurements. TABLE 3
Figure imgf000047_0001
Further Inventive Concepts
1. A one dimensional photonic crystal comprising: a first dielectric layer having a refractive index ¾ and comprising a fluoropolymer; a second dielectric layer having a refractive index n2 ≠ ¾ and comprising a second polymer composition. 2. The inventive concept 1, wherein the fluoropolymer is a polymer comprising an alicyclic structure in the polymer main chain or an elastomer comprising a fluoropolyether chain. 3. The inventive concept 1 or 2, wherein the photonic crystal has a thermal shielding of between about 5% to about 75% when irradiated with light having a power of about 150 W, a colour temperature of about 3500 K and a spot size of about 4.75 mm, relative to a glass substrate having substantially the same dimensions. 4. Any of the inventive concepts 1 to 3, wherein the photonic crystal has a thermal shielding of at least about 20% when irradiated with light having a power of about 150 W, a colour temperature of about 3500 K and a spot size of about 4.75 mm, relative to a glass substrate having substantially the same dimensions.
5. Any of the inventive concepts 1 to 4, wherein the one-dimensional photonic crystal comprises a plurality of first dielectric layers and a plurality of second dielectric layers, wherein the first dielectric layers and second dielectric layers are alternately stacked. 6. Any of the inventive concepts 1 to 5, wherein the one-dimensional photonic crystals comprises from 5 to 100 first dielectric layers and from about 5 to 100 second dielectric layers. 7. Any of the inventive concepts 1 to 6, wherein the one-dimensional photonic crystal comprises from 5 to 50 first dielectric layers and from about 5 to 50 second dielectric layers.
8. Any of the inventive concepts 1 to 7, wherein the one-dimensional photonic crystal has a band gap from about 300 nm to about 3000 nm. 9. The inventive concept 8, wherein the one-dimensional photonic crystal has a band gap from about 800 nm to about 2500 nm. 10. The inventive concept 8 or 9, wherein the one-dimensional photonic crystal has a band gap from about 800 nm to about 2000 nm. 11. Any of the inventive concepts 8 to 10, wherein the band gap is a first order band gap. 12. Any of the inventive concepts 1 to 11, wherein the one-dimensional photonic crystal has a second order band gap from about 600 nm to about 1300 nm.
13. Any of the inventive concepts 1 to 12, wherein the first dielectric layer has a thickness of from about 50 nm to about 5 μιη. 14. Any of the inventive concepts 1 to 13, wherein the first dielectric layer has a thickness of from about from about 100 nm to about 2 μιη. 15. Any of the inventive concepts 1 to 14, wherein the second dielectric layer has a thickness of from about 100 nm to about 2 μιη. 16. Any of the inventive concepts 1 to 15, wherein the first dielectric layer has a thickness of and where the at least one second dielectric layer has a thickness of about and wherein ο is from about from about 800 nm to about 2500 nm.
17. Any of the inventive concepts 1 to 16, wherein the photonic crystal has at least 10 repeat units, wherein 10 sequential repeat units have a reflectivity of at least 50% for a wavelength from about 300 nm to about 3000 nm, and wherein each of the 10 sequential repeat units comprises the first dielectric layer and the second dielectric layer in a stacked configuration. 18. Any of the inventive concepts 1 to 17, wherein the photonic crystal has at least 10 repeat units in a stacked configuration, wherein 10 sequential repeat units have a reflectivity of at least 50% for a wavelength from about 800 nm to about 1700 nm, and wherein each of the 10 sequential repeat units comprises the first dielectric layer and the second dielectric layer in a stacked configuration. 19. Any of the inventive concepts 1 to 18, wherein the photonic crystal has at least 10 repeat units in a stacked configuration, wherein 10 sequential repeat units have a reflectivity of at least 70% for a wavelength from about 300 nm to about 3000 nm, and wherein each of the 10 sequential repeat units comprises the first dielectric layer and the second dielectric layer in a stacked configuration. 20. Any of the inventive concepts 1 to 19, wherein the photonic crystal has at least 10 repeat units in a stacked configuration, wherein 10 sequential repeat units have a reflectivity of at least 70% for a wavelength from about 800 nm to about 1700 nm, and wherein each of the 10 sequential repeat units comprises the first dielectric layer and the second dielectric layer in a stacked configuration.
21. Any of the inventive concepts 1 to 20, wherein ¾ is from about 1.1 to about 1.6. 22. Any of the inventive concepts of 1 to 21, wherein |n2-ni | is from about 0.1 to about 0.7. 23. Any of the inventive concepts of 1 to 22, wherein |n2- ni | is from about 0.1 to about 0.4. 24. Any of the inventive concepts 1 to 23, wherein n2 > ¾ .
25. Any of the inventive concepts 1 to 24, wherein the f uoropolymer is a polymer comprising an alicyclic structure in the polymer main chain and comprising recurring units represented by: (A) the fluorodioxoles of formula (I):
2
Figure imgf000050_0001
(I)
wherein Ri, R2, R3 and R4, equal to or different from each other, are independently selected from the group consisting of -F, a Ci-C6 fluoroalkyl, optionally comprising one or more oxygen atoms, a Ci-C6 fluoroalkoxy, optionally comprising one or more oxygen atoms;
(B) the fluorodioxolanes of formula II):
Figure imgf000050_0002
(II)
wherein R5 and R6, equal to or different from each other, are independently selected from the group consisting of -F, a Ci-C6 fluoroalkyl, optionally comprising one or more oxygen atoms, a Ci-C6 fluoroalkoxy, optionally comprising one or more oxygen atoms; or
(C) the cyclopolymerizable monomers of formula (III):
CR7R8=CR9OCRioRii(CRi2Ri3)a(0)bCRi4=CRi (III) wherein each R7 to Ri6, independently of one another, is selected from -F, and a C1-C3 fluoroalkyl, a is 0 or 1 , b is 0 or 1 with the proviso that b is 0 when a is 1. 26. The inventive concept 25, wherein the fluoropolymers are the copolymers of tetrafluoroethylene and the fluorodioxoles of formula (I) having Ri=R3=R4 = -F and R2 = -OCF3 or wherein Ri=R2= -F and R3=R4= -CF3.
27. Any of the inventive concepts 1 to 24, wherein the fluoropolymer is an elastomer comprising a fluoropoly ether chain, obtained by the UV-curing of compositions comprising: at least one functional fluoropoly ether compound comprising a fluoropolyoxyalkylene chain (Rf) and having at least two unsaturated moieties; and at least one photoinitiator. 28. The inventive concept 27, wherein the functional fluoropolyether compound is selected from the group consisting of compounds of formula (IV):
Ti-J-RrJ' -T2, (IV)
wherein
Rf represents a fluoropolyoxyalkylene chain comprising recurring units having general formula: -(CF2)k-CFZ-0-, wherein k is an integer of from 0 to 3 and Z is a fluorine atom or a C1-C5 perfluoroalkyl group, optionally comprising one or more oxygen atom;
J and J' , equal to or different from each other, are independently a bond or a divalent bridging group, and
Ti and T2, equal to or different from each other, are selected from the group consisting of:
(A) -0-CO-CRH=CH2,
(B) -0-CO-NH-CO-CRH=CH2, and
(C) -0-CO-RA-CRH=CH2,
wherein RH is H or a Ci-C6 alkyl group; RA is selected from the group consisting of:
(j) -NH-RB-0-CO-
(jj) -NH-RB-NHCOO-RB-OCO-;
wherein RB is a divalent group selected from the group consisting of C1-C10 aliphatic group, C5-C14 cyclo aliphatic group; C6-Ci4 aromatic or alkylaromatic group.
29. Any of the inventive concepts 1 to 28, wherein the second dielectric layer comprises poly(methyl methacrylate), polycarbonate, polystyrene, cellulose acetate, poly( vinyl carbazole), or any combination thereof.
30. A method of making a one-dimensional photonic crystal, the method comprising:
forming a first layer on a substrate, the forming comprising spin-coating a first precursor solution onto the substrate, wherein the first precursor solution comprises a solvent and from about 0.1% weight by volume to about 50% weight by volume of a fluoropolymer and wherein the substrate is spun at a speed of about 1000 rpm to about 20000 rpm. 31. The inventive concept 30, wherein the substrate is spun at a speed of 200 rpm to about 15000 rpm. 32. The inventive concept 30 or 31, wherein the substrate is spun at a speed from about 1000 rpm to about 15000 rpm. 33. Any of the inventive concepts 30 to 32, wherein the substrate is spun for at least 5 minutes. 34. Any of the inventive concepts 30 to 32, wherein the substrate is spun from about 5 seconds to about 5 minutes.
35. Any of the inventive concepts 30 to 34, wherein the forming further comprises plasma treating the spin-coated first precursor solution, wherein the plasma treating comprises exposing the spin-coated first precursor solution to a plasma having a power density from about 1W/L to about 100 W/L. 36. The inventive concept 35, wherein the plasma has a power density from about 1W/L to about 100 W/L. 37. The inventive concept 35 or 36, wherein the plasma has a power density from about 1W/L to about 50 W/L. 38. Any of the inventive concepts 35 to 37, wherein the spin-coated first precursor solution is exposed to the plasma from about 1 second to about 5 minutes. 39. Any of the inventive concepts 35 to 38, wherein the spin-coated first precursor solution is exposed to the plasma from about 30 seconds to about 5 minutes. 40. Any of the inventive concepts 35 to 39, wherein the plasma treatment is performed in a plasma chamber having a pressure of no more than about 10 millibar ("mbar"). 41. The inventive concept 40, wherein the plasma chamber has a pressure of no more than about 5 mbar. 42. Any of the inventive concepts 30 to 41, further comprising heating the spin-coated first precursor solution by heating to remove solvent.
43. Any of the inventive concepts 30 to 42 wherein the solvent comprises a perfluoropoly ether, a hydro fluoroether or a combination thereof. 44. Any of the inventive concepts 30 to 43, wherein the substrate comprises a second layer and wherein the first precursor solution is deposited on the second layer. 45. The inventive concept 44, wherein the second layer comprises a polymer composition distinct from the fluoropolymer composition. 46. The inventive concept 44 or 45, wherein the second layer comprises poly(methyl methacrylate), polycarbonate, polystyrene, cellulose acetate, poly(vinyl carbazole), or any combination thereof.
47. Any of the inventive concepts 30 to 46, wherein the fluoropolymer is a polymer comprising an alicyclic structure in the polymer main chain and comprising recurring units represented by::
(A) the fluorodioxoles of formula (I):
R1 R2
R3 R4
(I)
wherein Ri, R2, R3 and R4, equal to or different from each other, are independently selected from the group consisting of -F, a Ci-C6 fluoroalkyl, optionally comprising one or more oxygen atoms, a Ci-C6 fluoroalkoxy, optionally comprising one or more oxygen atoms;
(B) the fluorodioxolanes of formula (II):
Figure imgf000053_0001
(II)
wherein R5 and R6, equal to or different from each other, are independently selected from the group consisting of -F, a Ci-C6 fluoroalkyl, optionally comprising one or more oxygen atoms, a Ci-C6 fluoroalkoxy, optionally comprising one or more oxygen atoms; or
(C) the cyclopolymerizable monomers of formula (III):
CR7R8=CR9OCRioRii(CRi2Ri3)a(0)bCRi4=CRi5Ri6, (III) wherein each R7 to Ri6, independently of one another, is selected from -F, and a C1-C3 fluoroalkyl, a is 0 or 1, b is 0 or 1 with the proviso that b is 0 when a is 1. 48. The inventive concept 47, wherein the fluoropolymers are the copolymers of tetrafluoroethylene and the fluorodioxoles of formula (I) having Ri=R3=R4 = -F and R2 = -OCF3 or wherein Ri=R2= -F andR3=R4= -CF3.
49. Any of the inventive concepts 30 to 46, wherein the fluoropolymer is an elastomer comprising a fluoropolyether chain, obtained by the UV-curing of compositions comprising: at least one functional fluoropolyether compound comprising a fluoropolyoxyalkylene chain (Rf) and having at least two unsaturated moieties; and at least one photoinitiator. 50. The inventive concept 49, wherein the functional fluoropolyether compound is selected from the group consisting of compounds of formula (IV):
Ti-J-R J' -T2, (IV)
wherein
Rf represents a fluoropolyoxyalkylene chain comprising recurring units having general formula: -(CF2)k-CFZ-0-, wherein k is an integer of from 0 to 3 and Z is a fluorine atom or a C1-C5 perfluoroalkyl group, optionally comprising one or more oxygen atom;
J and J' , equal to or different from each other, are independently a bond or a divalent bridging group, and
Ti and T2, equal to or different from each other, are selected from the group consisting of:
(A) -0-CO-CRH=CH2,
(B) -0-CO-NH-CO-CRH=CH2, and
(C) -0-CO-RA-CRH=CH2,
wherein RH is H or a Ci-C6 alkyl group; RA is selected from the group consisting of:
(j) -NH-RB-0-CO-
(jj) -NH-RB-NHCOO-RB-OCO-; wherein R is a divalent group selected from the group consisting of Ci-Cio aliphatic group, C5-C14 cycloaliphatic group; C6-Ci4 aromatic or alkylaromatic group.
51. Any of the inventive concepts 30 to 50, wherein the thickness of the first layer does not vary by more than about 20%. 52. The inventive concept 51 , wherein the thickness of the first layer does not vary by more than about 10%. 53. The inventive concept 52, wherein the thickness of the first layer does not vary by more than about 5%. 54. Any of the inventive concepts 30 to 53, wherein the first precursor solution comprises 0.1 % weight by volume to about 20% weight by volume of the fluoropolymer. 55. Any of the inventive concepts 30 to 54, wherein the photonic crystal is the photonic crystal of any of the inventive concepts 1 to 29 and wherein the first layer is the first dielectric layer. 56. Any of the inventive concepts 1 to 29, wherein the one-dimensional photonic crystal comprises at least 2 set of repeating units and wherein a first set of the at least 2 sets comprises the first and second dielectric layers. Any of the inventive concepts 1 to 29 or 56, wherein at least 2 sets of the at least 2 sets are spaced apart from eachother by another dielectric material.
The embodiments above are intended to be illustrative and not limiting. Additional embodiments are within the inventive concepts. In addition, although the present invention has be described with reference to particular embodiments, those skilled in the art will recognized that changes can be made in form and detail without departing form the spirit and scope of the invention. Any incorporation by reference of documents above is limited such that no subject matter is incorporated that is contrary to the explicit disclosure herein.
Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

Claims

C L A I M S
1. A method of making the one-dimensional photonic crystal, the method comprising: forming a first layer on a substrate, the forming comprising spin-coating a first precursor solution onto the substrate to form a coated substrate and plasma treating the coated substrate, wherein the first precursor solution comprises a solvent and from about 0.1% weight by volume to about 50%> weight by volume of a fluoropolymer and wherein the fluoropolymer comprises an alicyclic structure in the polymer main chain and recurring units represented by:
(A) the fluorodioxoles of formula (I):
R1 R2
Cv
R3 R4
(I) wherein Ri, R2, R3 and R4, equal to or different from each other, are independently selected from the group consisting of -F, a Ci-C6 fluoroalkyl, optionally comprising one or more oxygen atoms, a Ci-C6 fluoroalkoxy, optionally comprising one or more oxygen atoms;
(B) the fluorodioxolanes of formula (II):
Figure imgf000056_0001
(II) wherein R5 and Re, equal to or different from each other, are independently selected from the group consisting of -F, a Ci-C6 fluoroalkyl, optionally comprising one or more oxygen atoms, a Ci-C6 fluoroalkoxy, optionally comprising one or more oxygen atoms; or (C) the cyclopolymerizable monomers of formula (III):
Figure imgf000057_0001
wherein each R7 to Ri6, independently of one another, is selected from -F, and a C1-C3 fluoroalkyl, a is 0 or 1, b is 0 or 1 with the proviso that b is 0 when a is 1.
2. The method of claim 1, wherein the wherein the substrate is spun at a speed from about 100 rpm to about 20,000 rpm, preferably from about 1,000 rpm to 20,000 rpm, more preferably from 1000 rpm to about 15000 rpm.
3. The method of any one of claims 1 or 2, wherein the plasma treating comprises exposing the coated substrate to a plasma having a power density from about 1 W/L to about 100 W/L, preferably from about 1 W/L to about 50 W/L.
4. The method of any one of claims 1 to 3, wherein the coated substrate is exposed to the plasma from about 1 second to about 5 minutes.
5. The method of any one of claims 1 to 4, wherein the substrate comprises a second layer; wherein the second layer comprises a polymer composition distinct from the fluoropolymer composition; and wherein the first precursor solution is deposited on the second layer.
6. The method of claim 5, wherein the polymer composition comprises poly(methyl methacrylate), polycarbonate, polystyrene, cellulose acetate, poly(vinyl carbazole) or any combination thereof.
7. The method of any of claims 1 to 6, wherein the fluoropolymer is an elastomer comprising a fluoropolyether chain, obtained by the UV-curing of compositions comprising: at least one functional fluoropolyether compound comprising a fluoropolyoxyalkylene chain (Rf) and having at least two unsaturated moieties; and at least one photoinitiator.
8. The method of claim 7, wherein the functional fluoropolyether compound is selected from the group consisting of compounds of formula (IV):
Ti-J-RrJ' -T2, (IV) wherein
Rf represents a fluoropolyoxyalkylene chain comprising recurring units having general formula: -(CF2)k-CFZ-0-, wherein k is an integer of from 0 to 3 and Z is a fluorine atom or a C1-C5 perfluoroalkyl group, optionally comprising one or more oxygen atom;
J and J' , equal to or different from each other, are independently a bond or a divalent bridging group, and
Ti and T2, equal to or different from each other, are selected from the group consisting of:
(A) -0-CO-CRH=CH2,
(B) -0-CO-NH-CO-CRH=CH2, and
(C) -0-CO-RA-CRH=CH2, wherein RH is H or a Ci-C6 alkyl group; RA is selected from the group consisting of:
(j) -NH-RB-0-CO-
(jj) -NH-RB-NHCOO-RB-OCO-; wherein RB is a divalent group selected from the group consisting of C1-C10 aliphatic group, C5-C14 cycloaliphatic group; C6-Ci4 aromatic or alkylaromatic group.
9. The method of any one of claims 1 to 8, wherein the solvent comprises a perfluoropolyether, a hydrofluoroether or a combination thereof.
10. The method of any one of claims 1 to 9, wherein the thickness of the first layer does not vary by mare than about 20%.
11. The method of any one of claims 1 to 10, wherein the first precursor solution comprises about 0.1 % weight by volume to about 20%> weight by volume of the fluoropolymer.
12. The method of any one of claims 1 to 1 1 , further comprising heating the spin-coated first precursor solution to remove solvent.
13. The method of any one of claims 1 to 12, wherein the one-dimensional photonic crystal has a band gap from about 300 nm to about 3000 nm.
14. The method of any one of claims 1 to 13, wherein the first layer has a thickness of from about 50 nm to about 5 μιη.
15. The method of any one of claims 1 to 14, wherein the photonic crystal has a thermal shielding of between about 5% to about 75% when irradiated with light having a power of about 150 W, a colour temperature of about 3500 K and a spot size of about 4.75 mm, relative to a glass substrate having substantially the same dimensions.
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