JP4671028B2 - Photonic crystal refractive index control method - Google Patents

Description

  The present invention relates to a method for controlling the refractive index of a photonic crystal.

  In recent years, research using three-dimensional periodic structures of fine particles has been actively conducted in a wide range of fields such as catalysts, recording materials, sensors, electronic devices, and optical devices. In particular, in the field of optical materials, interest in photonic crystals has increased, and research on producing two-dimensional or three-dimensional photonic crystals from a regular array of fine particles has been actively conducted. Here, the photonic crystal is a crystal in which two or more materials having different refractive indexes are periodically arranged. Due to such a regular periodic structure, the photonic crystal exhibits characteristics that cannot be obtained with conventional optical materials. The most characteristic point of such a photonic crystal is a photonic band gap. The photonic band gap is an energy band of light that cannot propagate when light travels through the photonic crystal, and light having a wavelength corresponding to such an energy band cannot pass through the photonic crystal. Therefore, in such a photonic crystal, for example, a defect is introduced into the photonic crystal, and light having a wavelength corresponding to the photonic band gap is transmitted only through the defective portion in the photonic crystal, so that a small area is obtained. It is possible to control the light. Photonic crystals having such characteristics are very useful in the optical field, and in particular, there is an increasing expectation for photonic crystals in which spherical fine particles such as polystyrene and silica that can be studied on a laboratory scale are arranged.

  For example, in Japanese Patent Application Laid-Open No. 2004-240008 (Patent Document 1), in a fine particle structure in which fine particles are regularly arranged three-dimensionally, the fine particles 1 made of the material a, the core of the material b, and the outside of the material c. A fine particle structure formed of fine particles 2 having a multi-layer structure composed of shells, wherein the fine particles 1 and the fine particles 2 have the same particle diameter and the same shape, and the fine particles 2 are introduced at arbitrary positions. It is disclosed. However, such a fine particle structure described in Patent Document 1 is not practical because the manufacturing process is complicated. Further, in such a fine particle structure, the refractive index could not be arbitrarily changed after the production.

  In JP-A-2005-82746 (Patent Document 2), a layer in which a crosslinked hydrophilic organic polymer compound and an inorganic oxide are integrated, and fine particles included in the layer. And a three-dimensional periodic structure in which the fine particles are arranged with a three-dimensional period is disclosed. However, in such a three-dimensional periodic structure described in Patent Document 2, it is necessary to go through many production steps for the production thereof, and not only the steps are complicated, but the method for arranging the core-shell particles is unclear. Therefore, an array with high regularity has not been obtained. Further, in such a three-dimensional periodic structure, the configuration of the array once manufactured cannot be changed, so that the refractive index cannot be arbitrarily changed after manufacture.

  Moreover, in JP-A-2004-46224 (Patent Document 3), the particle diameter is smaller than the fine particles between the fine particles of the opal structure formed by periodically arranging fine particles having the same particle diameter, and the fine particles are Filling with nano-sized particles of different components to form a particle film, and then removing the fine particles from the particle film to form an inverse opal structure in which spherical spaces are periodically arranged, and the inverse opal A photonic crystal containing a photoresponsive liquid crystal is disclosed in which each spherical space of a structure is filled with a mixture of a compound causing photoisomerization and a nematic liquid crystal. However, in the photonic crystal described in Patent Document 3, photoresponsiveness can be obtained, but since the wavelength control is determined by the polystyrene particle diameter used, only one wavelength can be switched, The refractive index could not be arbitrarily changed after the photonic crystal was manufactured.

  Furthermore, a method for producing a photonic crystal by changing the interval of the array instead of the refractive index after producing the structure has also been reported (SH Foulger, P. Jiang, A. Lattam, D. W. Smith Jr, J. Ballato, D. E. Dausch, S. Grego, B. R. Stoner, “Photonic Crystal Composites with Reverse High-Frequency Stop 3”. No15, P685-P689 (refer nonpatent literature 1). In such a photonic crystal, a regular structure of colloidal particles is used as a template, a hydrogel is introduced into the gap to produce a strong structure, and this hydrogel absorbs the solvent and swells. Attempts to control particle spacing. However, in order to utilize the swelling property of hydrogel, there are restrictions on the solvent that can be used. In addition, it takes a lot of time to produce a colloidal crystal as a template. Further, since the organic or inorganic material is filled in the gaps between the closely packed particles, it has been difficult to uniformly fill the inside depending on the substance to be filled.

Japanese Patent Laid-Open No. 2003-202402 (Patent Document 4) is a method for controlling the periodic structure of a periodic structure in which an optical medium is periodically arranged in or on a substrate, and the period A method for controlling a periodic structure of a periodic structure is disclosed that includes a step of applying an external field to the periodic structure, thereby causing a dimensional change in the substrate. However, in such a periodic structure control method, in order to apply a magnetic field, a specialized device is required, which increases costs. Further, since it is necessary to regularly arrange the particles on two types of substrates, a magnetostrictive material substrate and a non-magnetic substrate, the manufacturing process is complicated.
Japanese Patent Laid-Open No. 2004-240008 JP 2005-82746 A JP 2004-46224 A Japanese Patent Laid-Open No. 2003-202402 S. H. Foulger, P.A. Jiang, A .; Lattam, D.C. W. Smith Jr, J. Ballato, D.M. E. Dausch, S .; Grego, B.M. R. Stoner. , “Photonic Crystal Composites with Reversible High-Frequency Stop Band Shifts” Adv. Mater, published in 2003, No15, P685-P689

  The present invention has been made in view of the above-mentioned problems of the prior art, and is a photonic crystal capable of arbitrarily changing the refractive index of a photonic crystal by a simple method without requiring a special device. An object of the present invention is to provide a refractive index control method.

  As a result of intensive studies to achieve the above object, the present inventors first adsorb various substances according to atmosphere, pressure, etc. by regularly arranging spherical silica-based mesoporous materials. Can be obtained, and by introducing various substances into the mesopores of the photonic crystal thus obtained, the refractive index of the photonic crystal can be arbitrarily controlled. As a result, the present invention has been completed.

That is, the method for controlling the refractive index of a photonic crystal according to the present invention is a method for controlling the refractive index of a photonic crystal in which spherical silica-based mesoporous materials are arranged, and the mesopores of the spherical silica-based mesoporous material Introducing a desorbable substance into the mesopores and reversibly controlling the refractive index of the photonic crystal by increasing or decreasing the concentration of the substance or replacing the substance with another substance It is the method characterized by this.

  In the present invention, the spherical silica-based mesoporous material has an average particle diameter of 0.01 to 3 μm, and the spherical silica-based mesoporous material has a central pore diameter of 1.8 to 5 nm. preferable.

As the removable substance into mesopores according to the present invention, water is preferably at least one material selected from the group consisting of organic solvents, complex body and an organic dye.

Although the reason why the refractive index of the photonic crystal can be changed by a simple method by the method of controlling the refractive index of the photonic crystal of the present invention is not necessarily clear, the present inventors have as follows. I guess. That is, normally, in a photonic crystal using spherical particles, the spherical particles are arranged in a close-packed structure, and the proportion of the spherical particles in the structure is about 26%. The wavelength of the stop band in such a photonic crystal is defined by the Bragg diffraction equation (1) below. Further, for example, the refractive index of the array when the number of substances introduced into the pores is one is expressed by the following formulas (2) and (3).
λ = 2 × (2/3) ^1/2 d {(n _eff ) ² −sin ² θ} ^1/2 (1)
(N _eff ) = {0.26 × n ₁ ² + 0.74 × (n _{porous body} ) ² } ^1/2 (2)
(N _{porous body} ) = {V × n ₂ ² + (1−V) × (n _oxide )} ^1/2 (3)
(In the formulas (1) to (3), λ represents a peak wavelength, d represents a particle diameter of a spherical particle, θ represents an incident angle of light, and (n _eff ) is a photo obtained by the formula (2). the refractive index of the entire photonic crystal, n ₁ is the refractive index of the atmosphere (air) present in the array, n _{porous body} is the refractive index of the spherical mesoporous silica material, V is spherical mesoporous silica Represents the ratio of the pore volume to the total volume of the body, n ₂ represents the refractive index of the substance filled in the mesopores, and n _{oxide represents} the refraction of silica itself used as a raw material for the spherical silica-based mesoporous material Indicates the rate.)

In the present invention, since the arranged spherical particles are spherical silica-based mesoporous materials, the ratio (V) of the pore volume to the total volume of the spherical silica-based mesoporous materials and the substances filled in the mesopores By changing the refractive index n ₂ , the refractive index n _{eff of the} entire photonic crystal can be directly changed easily according to the above formulas (2) and (3). As described above, in the photonic crystal used in the present invention, since various substances can be introduced into the mesopores of the spherical silica-based mesoporous material, the refractive index can be arbitrarily changed without fixing. The present inventors speculate that this is possible. Further, in the present invention, a substance that can be desorbed into the mesopores of the spherical silica-based mesoporous material is introduced into the mesopores, and the concentration thereof is increased or decreased or replaced with other substances. Thus, the present inventors infer that the refractive index can be changed more dynamically.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the refractive index control method of the photonic crystal which can change the refractive index of a photonic crystal arbitrarily by a simple method, without requiring a special apparatus.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

  First, the spherical silica mesoporous material used in the present invention will be described. The spherical silica-based mesoporous material used in the present invention is not particularly limited as long as it is a spherical silica-based mesoporous material having uniform and regular channel mesopores, but those described in detail below are preferable. By using such a spherical silica-based mesoporous material, it is possible to adsorb or introduce various substances into the mesopores under arbitrary conditions after the photonic crystal is manufactured.

  The spherical silica-based mesoporous material suitable for the present invention has an average particle size of 0.01 to 3 μm (more preferably 0.1 to 1 μm). If the average particle size of such a spherical silica-based mesoporous material is less than the lower limit, the process of separating the particles from the synthesis solution tends to be difficult during synthesis, whereas if the upper limit is exceeded, the particle size is large. Is very large compared to the wavelength of light, so that it tends not to function as a photonic crystal.

  In addition, the spherical silica-based mesoporous material suitable for the present invention has a central pore diameter of 1.8 to 5 nm. When the diameter of the central pore of such a spherical silica-based mesoporous material is less than the lower limit, a pore volume effective for introducing a substance tends to be insufficient, and on the other hand, when the upper limit is exceeded, it is obtained. The uniformity of the pore diameter tends to decrease.

  Further, as the spherical silica-based mesoporous material used in the present invention, 90% by mass or more of all the spherical silica-based mesoporous materials used has a particle diameter within a range of ± 10% of the average particle diameter. It is preferable that it has. In this way, the spherical silica mesoporous material having a particle size in the range of ± 10% of the average particle size is used at a ratio of 90% by mass or more, so that the spherical silica mesoporous material is uniformly obtained. It becomes possible to manufacture a photonic crystal in which bodies are arranged, and it is possible to more suitably use the photonic crystal in an optical device or the like.

  Here, the term “spherical” as used in the present invention is not limited to a true sphere, but includes a substantially sphere having a minimum diameter of 80% or more (preferably 90% or more) of the maximum diameter. . In the case of a substantially spherical body, the particle size is an average value of the minimum diameter and the maximum diameter in principle. Further, the central pore diameter is a curve (pore diameter distribution curve) in which a value (dV / dD) obtained by differentiating the pore volume (V) with respect to the pore diameter (D) is plotted against the pore diameter (D). ) At the maximum peak. The pore size distribution curve can be obtained by the method described below. That is, silica-based mesoporous particles are cooled to a liquid nitrogen temperature (-196 ° C.), nitrogen gas is introduced, the adsorption amount is determined by a constant volume method or a gravimetric method, and then the pressure of the introduced nitrogen gas is gradually increased. And the adsorption amount of nitrogen gas for each equilibrium pressure is plotted to obtain an adsorption isotherm. Using this adsorption isotherm, a pore size distribution curve can be obtained by a calculation method such as Cranston-Inklay method, Pollimore-Heal method, BJH method or the like.

Further, the spherical silica-based mesoporous material is more preferably one in which 60% or more of the total pore volume is included in the range of ± 40% of the central pore diameter in the pore diameter distribution curve. Silica-based mesoporous particles satisfying such conditions have a very uniform pore diameter. By using a spherical silica-based mesoporous material having a uniform pore diameter, various substances can be introduced uniformly into the pores, and the refractive index can be controlled more efficiently. It is possible to manufacture a photonic crystal that can be performed easily. The specific surface area of such a spherical silica-based mesoporous material is not particularly limited, but is preferably 700 m ² / g or more. The specific surface area can be calculated as a BET specific surface area from the adsorption isotherm using the BET isotherm adsorption equation.

  Further, such a spherical silica-based mesoporous material preferably has one or more peaks at a diffraction angle corresponding to a d value of 1 nm or more in the X-ray diffraction pattern. The X-ray diffraction peak means that a periodic structure having a d value corresponding to the peak angle is present in the sample. Therefore, having one or more peaks at a diffraction angle corresponding to a d value of 1 nm or more means that the pores are regularly arranged at intervals of 1 nm or more.

  In addition, the pores of such a spherical silica-based mesoporous material are formed not only on the surface of the porous material but also inside. The arrangement state (pore arrangement structure or structure) of the pores in such a porous body is not particularly limited, but is preferably a 2d-hexagonal structure, a 3d-hexagonal structure, or a cubic structure. Such a pore arrangement structure may have a disordered pore arrangement structure.

Here, that the porous body has a hexagonal pore arrangement structure means that the arrangement of the pores is a hexagonal structure (S. Inagaki, et.
al. , J .; Chem. Soc. , Chem. Commun. 680, 1993; Inagaki, et al. Bull. Chem. Soc. Jpn. 69, 1449, 1996; Huo, et al. Science, 268, 1324, 1995). Moreover, the porous body having a cubic pore arrangement structure means that the arrangement of the pores is a cubic structure (JC Vartuli, et al., Chem. Mater., 6, 2317, 1994). Q. Huo, et al., Nature, 368, 317, 1994). Further, that the porous body has a disordered pore arrangement structure means that the arrangement of the pores is irregular (PT Tanev, et al., Science, 267, 865, 1995; S; A. Bagshaw, et al., Science, 269, 1242, 1995; R. Ryoo, et al., J. Phys. Chem., 100, 17718, 1996). The cubic structure is preferably Pm-3n, Im-3m or Fm-3m symmetric. The symmetry is determined based on a space group notation.

  The spherical silica-based mesoporous material suitably used in the present invention has been described above. Next, an embodiment of a suitable manufacturing method for manufacturing such a spherical silica-based mesoporous material will be described. That is, as a suitable production method for producing a spherical silica mesoporous material suitably used in the present invention, a silica raw material and a surfactant are mixed in a solvent, and the surfactant is contained in the silica raw material. Including a first step of obtaining a porous precursor particle in which is introduced, and a second step of obtaining a spherical silica-based mesoporous material by removing the surfactant contained in the porous precursor particle A method is mentioned. Hereinafter, the first step and the second step will be described separately.

(First step)
In such a method for producing a spherical silica-based mesoporous material, first, a porous precursor particle obtained by mixing a silica raw material and a surfactant in a solvent and introducing the surfactant into the silica raw material. (First step).

  The silica raw material is not particularly limited as long as it can form a silicon oxide (including a silicon composite oxide) by reaction. From the viewpoint of reaction efficiency and physical properties of the obtained silicon oxide, alkoxysilane, silica It is preferable to use sodium acid, layered silicate, silica, or any mixture thereof, and it is more preferable to use alkoxysilane.

  As such an alkoxysilane, tetraalkoxysilane having 4 alkoxy groups, trialkoxysilane having 3 alkoxy groups, or dialkoxysilane having 2 alkoxy groups can be used. The type of alkoxy group is not particularly limited, but those having a relatively small number of carbon atoms in the alkoxy group (such as those having about 1 to 4 carbon atoms) such as methoxy group, ethoxy group, propoxy group, butoxy group, etc. This is advantageous in terms of reactivity. Further, when the alkoxysilane has 3 or 2 alkoxy groups, an organic group, a hydroxyl group, or the like may be bonded to the silicon atom in the alkoxysilane, and the organic group is an amino group, a mercapto group, or the like. It may further have a functional group.

  Examples of the tetraalkoxysilane include tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, and dimethoxydiethoxysilane. Examples of the trialkoxysilane include trimethoxysilanol, triethoxysilanol, Trimethoxymethylsilane, trimethoxyvinylsilane, triethoxyvinylsilane, 3-glycidoxypropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltri Methoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, γ- (methacryloxypropyl) trimethoxysilane, β- (3,4-epoxycyclohexyl) ethyl Examples include trimethoxysilane. Examples of the dialkoxysilane include dimethoxydimethylsilane, diethoxydimethylsilane, diethoxy-3-glycidoxypropylmethylsilane, dimethoxydiphenylsilane, and dimethoxymethylphenylsilane.

  Further, such alkoxysilanes can be used alone or in combination of two or more. Moreover, the alkoxysilane having 2 to 4 alkoxy groups described above can be used in combination with a monoalkoxysilane having one alkoxy group. Examples of the monoalkoxysilane that can be used in this way include trimethylmethoxysilane, trimethylethoxysilane, and 3-chloropropyldimethylmethoxysilane.

  Alkoxysilane produces a silanol group by hydrolysis, and the resulting silanol groups condense to form a silicon oxide. In this case, an alkoxysilane having a large number of alkoxy groups in the molecule has many bonds generated by hydrolysis and condensation. Therefore, in the present invention, tetraalkoxysilane having a large number of alkoxy groups is preferably used as alkoxysilane, and tetramethoxysilane or tetraethoxysilane is particularly preferably used as tetraalkoxysilane from the viewpoint of reaction rate.

Examples of sodium silicate used as the silica raw material include sodium metasilicate (Na ₂ SiO ₃ ), sodium orthosilicate (Na ₄ SiO ₄ ), sodium disilicate (Na ₂ Si ₂ O ₅ ), and tetrasilicate. sodium _(Na 2 _Si 4 _{O 9),} and the like. As the sodium silicate, in addition to such a single substance, water glass (Na ₂ O · nSiO ₂ , n = 2 to 4) or the like having a different composition depending on the case can be used.

Further, as the layered silicate, kanemite (NaHSi ₂ O ₅ .3H ₂ O), sodium disilicate crystal (α, β, γ, δ-Na ₂ Si ₂ O ₅ ), macatite (Na ₂ Si ₄ O ₉₎ · 5H ₂ O), ialite (Na ₂ Si ₈ O ₁₇ · xH ₂ O), magadiite (Na ₂ Si ₁₄ O ₁₇ · xH ₂ O), kenyaite (Na ₂ Si ₂₀ O ₄₁ · xH ₂ O), etc. Is mentioned. Further, a layer obtained by treating clay minerals such as sepiolite, montmorillonite, vermiculite, mica, kaolinite and smectite with an acidic aqueous solution to remove elements other than silica can be used as the layered silicate.

  Examples of the silica used as the silica raw material include precipitated silicas such as Ultrasil (Ultrasil), Cab-O-Sil (Cabot), HiSil (Pittsburgh Plate Glass); colloidal silica; Aerosil (Degussa-Huls), etc. Of fumed silica.

  The above silica raw materials can be used alone or in combination of two or more. However, when two or more types of silica raw materials are used, it is preferable to use a single silica raw material because the reaction conditions during production may be complicated.

  The surfactant is an alkyl ammonium halide represented by the following general formula (1).

[Wherein, R ¹ , R ² and R ³ may be the same or different and each represents an alkyl group having 1 to 3 carbon atoms, X represents a halogen atom, and n represents an integer of 13 to 25, respectively. ]
Thus, R < ¹ >, R < ² >, R < ³ > in General formula (1) may be same or different, and respectively shows a C1-C3 alkyl group. Examples of such an alkyl group include a methyl group, an ethyl group, and a propyl group, and these may be mixed in one molecule. From the viewpoint of symmetry of the surfactant molecule, R ¹ , R ² , R ³ Are preferably the same. When the symmetry of the surfactant molecule is excellent, aggregation of the surfactants (formation of micelles, etc.) tends to be facilitated. ^Furthermore, R ^1, it is preferable that at least one of R 2, ^{R 3} is a methyl ^group, and more preferably all of R ^1, R 2, ^{R 3} is a methyl group.

  Moreover, n in General formula (1) shows the integer of 13-25, and it is more preferable that it is an integer of 13-17. With the alkylammonium halide having n of 12 or less, a spherical porous body can be obtained, but the central pore diameter becomes smaller than 1.8 nm, and a substance having a large molecular weight cannot be introduced into the pores. . On the other hand, in the case of the alkylammonium halide having n of 26 or more, the hydrophobic interaction of the surfactant is too strong, so that a layered compound is generated and a spherical porous body cannot be obtained.

  Furthermore, X in the general formula (1) represents a halogen atom, and the kind of such a halogen atom is not particularly limited, but X is preferably a chlorine atom or a bromine atom from the viewpoint of easy availability.

Therefore, as the surfactant represented by the general formula (1), all of R ¹ , R ² and R ³ are methyl groups and alkyltrimethylammonium halides having a long-chain alkyl group having 14 to 26 carbon atoms. Among them, tetradecyltrimethylammonium halide, hexadecyltrimethylammonium halide, octadecyltrimethylammonium halide, eicosyltrimethylammonium halide, and docosyltrimethylammonium halide are more preferable.

  Such a surfactant forms a complex in a solvent together with the silica raw material. The silica raw material in the composite is changed to silicon oxide by the reaction, but silicon oxide is not generated in the part where the surfactant is present, so pores are formed in the part where the surfactant is present. Will be. That is, the surfactant is introduced into the silica raw material and functions as a template for pore formation. Further, such surfactants can be used alone or in combination of two or more, but as described above, the surfactant functions as a template for forming pores in the reaction product of the silica raw material. Since the type greatly affects the shape of the pores of the porous body, it is preferable to use only one type of surfactant in order to obtain a more uniform spherical porous body.

  As a solvent for mixing the silica raw material and the surfactant, a mixed solvent of water and alcohol is used. Examples of such alcohol include methanol, ethanol, isopropanol, n-propanol, ethylene glycol, and glycerin, and methanol or ethanol is preferable from the viewpoint of solubility of the silica raw material.

  When synthesizing the porous precursor particles in which the surfactant is introduced into the silica raw material, it is important to use a water / alcohol mixed solvent having an alcohol content of 45 to 80% by volume. More preferably, the alcohol content is 50 to 70% by volume. Thus, by using a mixed solvent containing a relatively large amount of alcohol, generation and growth of uniform spheres are realized, and the particle diameter of the resulting spherical silica-based mesoporous material is highly uniformly controlled. It will be. When the alcohol content is less than 45% by volume, it is difficult to control the particle size and particle size distribution, and the particle size uniformity of the resulting spherical silica mesoporous material is reduced. On the other hand, when the alcohol content exceeds 80% by volume, it is difficult to control the particle size and particle size distribution, and the uniformity of the particle size of the obtained spherical silica-based mesoporous material is lowered.

  Further, by changing the ratio of water and alcohol, the particle size of the obtained spherical silica mesoporous material can be easily controlled while maintaining the uniformity of the particle size at a high level. That is, when the water ratio is high, the porous body is likely to precipitate, so the particle size is small. Conversely, when the alcohol ratio is high, a porous body having a large particle size can be obtained.

  Furthermore, when the porous material precursor particles are obtained by mixing the silica raw material and the surfactant in the mixed solvent, the concentration of the surfactant described above is set to 0.003 to 0.00 on the basis of the total volume of the solution. 03 mol / L (preferably 0.01 to 0.02 mol / L), and the concentration of the silica raw material described above is 0.005 to 0.03 mol / L (preferably 0.008 to 0.015 mol / L). By strictly controlling the concentrations of the surfactant and the silica raw material in this way, the generation and growth of uniform spherical bodies can be realized in combination with the use of the above-mentioned mixed solvent, and the resulting spherical silica meso The particle size of the porous body is highly uniformly controlled. When the concentration of the surfactant is less than 0.003 mol / L, a sufficient porous body cannot be obtained because the amount of the surfactant to be a template is insufficient, and the particle size and particle size distribution are controlled. The particle size uniformity of the spherical silica-based mesoporous material obtained becomes difficult. On the other hand, when the concentration of the surfactant exceeds 0.03 mol / L, a porous body having a spherical shape cannot be obtained at a high ratio, and control of the particle size and particle size distribution becomes difficult. The uniformity of the particle size of the resulting spherical silica-based mesoporous material is reduced. In addition, when the concentration of the silica raw material is less than 0.005 mol / L, a porous body having a spherical shape cannot be obtained in a high ratio, and control of the particle size and particle size distribution becomes difficult. The uniformity of the particle size of the spherical silica-based mesoporous material is lowered. On the other hand, when the concentration of the silica raw material exceeds 0.03 mol / L, a good porous body cannot be obtained because the ratio of the surfactant to be a template is insufficient, and the particle size and particle size distribution are further reduced. The uniformity of the particle size of the spherical silica-based mesoporous material obtained because of difficulty in control becomes low.

  Moreover, when mixing the said silica raw material and the said surfactant, it is preferable to mix on basic conditions. The silica raw material generally reacts under basic and acidic conditions and changes to silicon oxide, but the concentration of the silica raw material and the surfactant is considerably lower than that of the prior art method. Therefore, the reaction hardly proceeds under acidic conditions. Therefore, when mixing the silica raw material and the surfactant, it is preferable to react the silica raw material under basic conditions. In addition, when the silica raw material is reacted under basic conditions, the reaction point of silicon atoms is increased when the reaction is performed under basic conditions, and a silicon oxide having excellent physical properties such as moisture resistance and heat resistance is obtained. In this respect, mixing under basic conditions is also advantageous.

  In order to make the mixed solvent basic, a basic substance such as an aqueous sodium hydroxide solution is usually added. There are no particular restrictions on the basic conditions during the reaction, but the value obtained by dividing the alkali equivalent of the basic substance to be added by the number of moles of silicon atoms in the total silica raw material should be 0.1 to 0.9. Preferably, it is more preferably 0.2 to 0.5. When the value obtained by dividing the alkali equivalent of the basic substance to be added by the number of moles of silicon atoms in the total silica raw material is less than 0.1, the yield tends to decrease, and on the other hand, it exceeds 0.9. In such a case, the formation of the porous body tends to be difficult.

  The reaction conditions (reaction temperature, reaction time, etc.) in the first step are not particularly limited, and the reaction temperature is, for example, -20 ° C to 100 ° C (preferably 0 ° C to 80 ° C, more preferably 10 ° C). ° C to 40 ° C). Further, the reaction is preferably allowed to proceed with stirring. Specific reaction conditions are preferably determined based on the type of silica raw material used.

  That is, when using alkoxysilane as a silica raw material, for example, porous precursor particles can be obtained as follows. First, a surfactant and a basic substance are added to a mixed solvent of water and alcohol to prepare a basic solution of the surfactant, and alkoxysilane is added to this solution. Since the added alkoxysilane is hydrolyzed (or hydrolyzed and condensed) in the solution, a white powder is deposited several seconds to several tens of minutes after the addition. In this case, the reaction temperature is preferably 0 ° C to 80 ° C, more preferably 10 ° C to 40 ° C. The solution is preferably stirred.

  After the precipitate is deposited, the solution is further stirred at 0 ° C. to 80 ° C. (preferably 10 ° C. to 40 ° C.) for 1 hour to 10 days to advance the reaction of the silica raw material. After completion of the stirring, if necessary, the system is allowed to stand overnight at room temperature to stabilize the system, and the resulting precipitate is filtered and washed as necessary to obtain porous precursor particles.

When silica raw material other than alkoxysilane (sodium silicate, layered silicate or silica) is used as the silica raw material, the silica raw material is added to a mixed solvent of water and alcohol containing a surfactant. A basic solution such as an aqueous sodium hydroxide solution is further added to prepare a uniform solution so as to have an equimolar amount with respect to the silicon atoms. Thereafter, porous precursor particles can be produced by a method in which a dilute acid solution is added in a molar amount of 1/2 to 3/4 times the silicon atoms in the silica raw material. The basic substance requires an excessive amount for the purpose of cleaving a part of the Si— (O—Si) ₄ bond already formed in the silica raw material, but it is necessary to neutralize the excess with an acid. There is. As the acid, any of inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as acetic acid may be used.

(Second step)
Next, in the second step, the surfactant contained in the porous precursor particles obtained in the first step is removed to obtain a spherical silica-based mesoporous material. Examples of the method for removing the surfactant as described above include a method by baking, a method of treating with an organic solvent, and an ion exchange method.

  In the method by firing, the porous precursor particles are heated at 300 to 1000 ° C, preferably 400 to 700 ° C. The heating time may be about 30 minutes, but it is preferable to heat for 1 hour or longer in order to completely remove the surfactant. The firing can be performed in the air, but since a large amount of combustion gas is generated, it may be performed by introducing an inert gas such as nitrogen. Moreover, when processing with an organic solvent, a porous body precursor particle is immersed in a good solvent with high solubility with respect to the used surfactant, and surfactant is extracted. In the ion exchange method, the porous precursor particles are immersed in an acidic solution (such as ethanol containing a small amount of hydrochloric acid) and stirred, for example, while heating at 50 to 70 ° C. Thereby, the surfactant existing in the pores of the porous precursor particles is ion-exchanged with hydrogen ions. In addition, although hydrogen ions remain in the hole by ion exchange, the problem of blockage of the hole does not occur because the ion radius of the hydrogen ion is sufficiently small.

  With such a production method, a spherical silica-based mesoporous material suitable for the present invention can be produced. That is, a spherical silica-based mesoporous material having an average particle size of 0.01 to 3 μm by the above-described production method, and 90% by mass or more (preferably 95% by mass or more) of the total particles obtained is an average particle size. Thus, it is possible to obtain a spherical silica-based mesoporous material having extremely high particle size uniformity having a particle size in the range of ± 10% and a relatively large central pore diameter of 1.8 to 5 nm.

  In addition, the spherical silica-based mesoporous material thus obtained is prepared using the surfactant as a template and the silica source as a raw material, and a skeleton-Si— in which silicon atoms are bonded through oxygen atoms. It is based on O- and has a highly crosslinked network structure. Further, such a silica-based material is only required to have a silicon atom and an oxygen atom as main components, and at least a part of the silicon atom forms a carbon-silicon bond at two or more sites of the organic group. But you can. Examples of such organic groups include divalent or higher valent organic groups generated by removing two or more hydrogens from hydrocarbons such as alkanes, alkenes, alkynes, benzenes, and cycloalkanes. Instead, the organic group may have an amide group, amino group, imino group, mercapto group, sulfone group, carboxyl group, ether group, acyl group, vinyl group or the like.

  Next, the photonic crystal used in the present invention will be described. The photonic crystal used in the present invention is formed by regularly arranging spherical silica-based mesoporous materials as described above. Therefore, the photonic crystal used in the present invention can adsorb various substances in the pores of the arranged spherical silica-based mesoporous materials, and can arbitrarily control the refractive index even after the array is produced. Is possible.

  The arrangement form of the spherical silica-based mesoporous material in such a photonic crystal is not particularly limited as long as the spherical silica-based mesoporous material is regularly arranged on the substrate. Specifically, it may be a planar arrangement form in which one layer of the spherical silica-based mesoporous material is arranged, or a three-dimensional arrangement form in which a plurality of layers are arranged. Examples of such a three-dimensional arrangement form include an arrangement form such as a hexagonal close-packed structure or a cubic close-packed structure.

  The method of arranging the spherical silica-based mesoporous material used for producing such a photonic crystal on the substrate is a method capable of regularly arranging the spherical silica-based mesoporous material on the substrate. There is no particular limitation, and a conventionally known method for arranging spherical silica-based mesoporous materials can be appropriately employed.

  Specific methods for arranging such spherical silica-based mesoporous materials include self-assembly of particles such as gravity sedimentation, forcing external force such as electricity and magnetic field from the outside, spin coating, etc. , A method of regularly arranging spherical silica-based mesoporous materials on a substrate by employing dip coating, or a method of regularly arranging spherical silica-based mesoporous materials on a substrate using microtweezers Etc. As a method for arranging such spherical silica-based mesoporous materials, for example, from the viewpoint of arbitrarily introducing a substance into the pores after preparing the array, for example, a dispersion of a spherical silica-based mesoporous material that is well dispersed It is preferable to employ a method in which spherical silica-based mesoporous materials are regularly arranged on the substrate by filling the glass between two glass plates and evaporating the solvent.

  In addition, the substrate used in manufacturing such a photonic crystal is not particularly limited as long as colloidal particles are easily arranged regularly, and a silicon wafer or the like can be used in addition to a glass substrate.

  The spherical silica-based mesoporous material used in the present invention has been described above. Next, the method for controlling the refractive index of the photonic crystal of the present invention will be described. That is, the refractive index control method for a photonic crystal of the present invention is a method for introducing a substance that can be introduced into the mesopores into the mesopores of the photonic crystal made of a spherical silica-based mesoporous material. . With such a refractive index control method, it is possible to arbitrarily change the refractive index of the photonic crystal by a simple method without requiring a special device.

  The substance that can be introduced into the mesopores used in the present invention is not particularly limited as long as it is a substance that can be introduced into the mesopores of the spherical silica-based mesoporous material, but water, an organic solvent, It is preferable to use at least one substance selected from the group consisting of metals, metal compounds, complexes and organic dyes.

Examples of such an organic solvent include toluene, benzene, acetone, ethanol, methanol, propanol, chlorobenzene, dichlorobenzene, hexane, chloroform, and the like. As the metal, gold (Au), platinum (Pt), silver ( Ag), palladium (Pd), rhodium (Rh), ruthenium (Ru) and the like. Examples of the metal compound include titanium oxide (TiO ₂ ), zinc oxide (ZnO), iron oxide (Fe ₂ O ₃ ), Examples thereof include zinc sulfide (ZnS), cadmium sulfide (CdS), cadmium selenide (CdSe), and the like. Examples of the complex include porphyrin complexes, chlorophyll derivatives, and ruthenium (Ru) complexes. Examples of the organic dyes include Rhodamine 6G, Rhodamine B, methylene blue, coumarin, and eosin. Moreover, the substance which can be introduce | transduced in such a mesopore can also be introduced individually by 1 type or in mixture of 2 or more types. Moreover, when using 2 or more types of substances which can be introduce | transduced in such a mesopore, it is also possible to use those substances in the state of a solution or a dispersion liquid.

  Further, the substance that can be introduced into the mesopores is more preferably a substance that can be desorbed into the mesopores. In this way, by using a detachable substance in the mesopores, the refractive index can be arbitrarily and reversibly changed (increased / decreased) according to the use state of the photonic crystal. Examples of the substance that can be desorbed into the mesopores include water, organic solvents having low viscosity such as toluene and benzene, and complexes and dyes having high solubility in them.

  A method for introducing a substance that can be introduced into the mesopores of the photonic crystal into the mesopores (hereinafter simply referred to as “introduction method”) is not particularly limited, and the mesopores are not limited. A suitable method is appropriately selected according to the type of substance that can be introduced into the inside, the target refractive index value, and the like. As such an introduction method, the photonic crystal is allowed to stand in the gas or liquid of the substance itself to be introduced into the mesopores, or in the gas or liquid containing the substance to be introduced into the mesopores. The method of doing can be mentioned. As such an introduction method, for example, when water is used as a substance to be introduced into the mesopores, the photonic crystal is allowed to stand in a constant temperature and humidity chamber under a predetermined condition, or an appropriate device is used. And a method of circulating steam. When a highly hydrophobic substance is used as the substance to be introduced into the mesopores, first, a coupling agent (for example, a silane coupling agent) is introduced into the mesopores of the photonic crystal. After hydrophobizing the inside of the pores, the photonic crystal is placed in a gas or liquid containing a highly hydrophobic substance to introduce a highly hydrophobic substance into the mesopores of the photonic crystal. It is preferable to adopt the method to do. In this way, first, by introducing a coupling agent into the mesopores of the photonic crystal to make the inside of the pores hydrophobic, the highly hydrophobic substance can be easily introduced. Become. Further, the method for removing the substance after the desorbable substance is introduced into the mesopores of the photonic crystal is not particularly limited, and a suitable method can be appropriately selected according to the introduced substance. .

  Further, the amount of the substance that can be introduced into the mesopores of the photonic crystal is not particularly limited, and the refractive index of the photonic crystal required when using the photonic crystal is not limited. Depending on the value, the introduction amount is appropriately changed and used. Therefore, in order to set the refractive index of the photonic crystal to a specific value, it is necessary to introduce the maximum amount that can be introduced into the mesopores. In the case where it is sufficient to introduce a predetermined amount of the substance that can be introduced into the mesopores in order to introduce the maximum possible amount of the substance and, on the other hand, to set the refractive index of the photonic crystal to a specific value. The predetermined amount of the substance that can be introduced into the mesopores is introduced.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

(Production Example 1: Production of spherical silica-based mesoporous material)
First, 7.04 g of hexadecyl (surfactant) and 9.12 g of 1N sodium hydroxide were added to a mixed solution of 800 g of water and 800 g of methanol. When 5.28 g of tetramethoxysilane (silica raw material) was added thereto and stirring was continued, tetramethoxysilane was completely dissolved, and a white powder was precipitated after about 200 seconds. Thereafter, the mixture was further stirred at room temperature for 8 hours and allowed to stand overnight (14 hours), and then the mixture was filtered and washed with deionized water three times to obtain a white powder (porous body precursor). Next, the white powder thus obtained was dried with a hot air dryer for 3 days, and then fired at a temperature condition of 550 ° C. for 6 hours to remove organic components including the surfactant from the white powder. A silica-based mesoporous material was obtained.

  A graph of the X-ray diffraction pattern of the spherical silica-based mesoporous material thus obtained is shown in FIG. The X-ray diffraction pattern shown in FIG. 1 shows that the obtained spherical silica-based mesoporous material has a two-dimensional hexagonal pore arrangement structure.

  Next, such a spherical silica-based mesoporous material was observed with a scanning electron microscope (SEM). The obtained SEM photograph is shown in FIG. It was confirmed that all of the spherical silica-based mesoporous materials observed by SEM have a spherical shape.

Furthermore, the water vapor adsorption isotherm of the spherical silica-based mesoporous material was measured under a temperature condition of 25 ° C. The obtained results are shown in FIG. As shown in FIG. 3, the spherical silica-based mesoporous material has a rapid water vapor adsorption when the relative vapor pressure (P / P ₀ ) is in the range of 0.3 to 0.5 (around 0.4). It was confirmed that the amount increased. From this fact, when the relative vapor pressure (P / P ₀ ) is less than 0.3, only one layer of water is adsorbed inside the pores of the spherical silica-based mesoporous material. On the other hand, when the value of the relative vapor pressure (P / P ₀ ) at which the curve rises rapidly exceeds 0.5, water vapor is introduced into the pores by capillary condensation phenomenon, and the spherical silica It was confirmed that the inside of the pores of the system mesoporous material was almost 100% filled with water vapor. Further, the adsorption isotherm having a sharp rise as shown in FIG. 3 is peculiar to a porous body having very uniform mesopores, so that the spherical silica-based mesoporous body is very uniform. It can be seen that it has regular channel mesopores.

(Production Example 2: Production of photonic crystal)
Using the spherical silica-based mesoporous material obtained in Production Example 1, this was dispersed in water to obtain a dispersion, and then the dispersion was filled between two glass plates. Thereafter, water evaporates, and the spherical silica-based mesoporous material was self-assembled to form an array, and a photonic crystal in which the spherical silica-based mesoporous material was arrayed on a glass substrate was obtained.

  The photonic crystal thus obtained was observed with a scanning electron microscope (SEM). The obtained SEM photograph is shown in FIG. 4 (magnification 20000 times) and FIG. 5 (magnification 5000 times). As is clear from the results shown in FIGS. 4 and 5, in such a photonic crystal, it is confirmed that the spherical silica-based mesoporous materials are regularly arranged in a close-packed structure in a wide range. It was.

Example 1
Using the photonic crystal obtained in Production Example 2, water vapor is introduced into the mesopores of the photonic crystal to change the refractive index, and the photonic before and after introducing water vapor into the mesopores. The reflection spectrum of the crystal was measured. That is, first, the water vapor in the mesopores of the photonic crystal was sufficiently removed by vacuum drying, and then the reflection spectrum of the photonic crystal was measured. Next, in order to introduce water vapor into the mesopores of the photonic crystal, the photonic crystal was left in a constant temperature and humidity chamber at a temperature of 30 ° C. and a relative humidity of 90% for 10 hours. Thus, after introducing water vapor into the mesopores of the photonic crystal, the reflection spectrum of the photonic crystal was measured. That is, this measurement corresponds to the case where the value of the relative vapor pressure (P / P ₀ ) on the water vapor adsorption isotherm in FIG. 3 is 0.25 and 0.90. Furthermore, when measuring the reflection spectrum of the photonic crystal, a halogen lamp (spot diameter: 5 mm) is used as a light source, and the incident angles of the irradiated light with respect to the photonic crystal are 9 °, 14 °, 20 °, respectively. It was changed to 24 °, 30 °, and 34 °. Then, the reflection spectra obtained by irradiating the photonic crystal with light having various incident angles were recorded. Among the obtained results, FIG. 6 shows a case where the value of P / P ₀ is 0.25, and FIG. 7 shows a case where the value of P / P ₀ is 0.90.

As is clear from the results shown in FIGS. 6 and 7, the photonic crystal has the incident angle of the irradiated light regardless of the value of P / P ₀ . Regardless of the difference, it was confirmed that a clear peak of the reflection spectrum was observed, and that the peak position of the reflection spectrum was regularly shifted to the lower wavelength side as the incident angle of the irradiated light increased. It was. From these results, it was confirmed that the regular arrangement of the spherical silica-based mesoporous material was not broken by the vacuum dryer and the introduction of water vapor. In addition, since water vapor was introduced in a gaseous state, it was confirmed that when the water vapor was introduced into the mesopores in the photonic crystal, the gap between the photonic crystals was not widened. From these results, it can be seen that there is no change in the interval of the particle array before and after the introduction of water vapor.

FIG. 8 is a graph plotting the relationship between the position of the reflection spectrum peak (λ) of the photonic crystal obtained in FIGS. 6 and 7 and the incident angle θ of light. As is apparent from the results shown in FIG. 8, the values of λ obtained with respect to the incident angle θ of light are the case where the value of P / P ₀ is 0.25 and the value of P / P ₀ is 0. In the case of 90, it was greatly different before and after the introduction of water vapor. In addition, since the arrangement interval (d) between the spherical silica-based mesoporous materials constituting the photonic crystal is unchanged before and after the introduction of water vapor as described above, in order to change λ shown in the Bragg diffraction conditions described above. For this, it is necessary that the refractive index n _{eff of the} entire photonic crystal shown in the Bragg diffraction condition is different. Actually, the refractive index of the entire photonic crystal obtained by analyzing the obtained reflection spectrum and substituting the numerical values into the equations (1) to (3) of the black analysis conditions described above is P / P ₀ . When the value is 0.25, n _eff = 1.1661 ± 0.00359, while when the value of P / P ₀ is 0.90, n _eff = 1.2348 ± 0.00559. since, the value of P / P _0, the value of the refractive index of the entire photonic crystal, was found to be different values. From these facts, in the spherical silica-based mesoporous material having uniform and regular channel mesopores, the refractive index of the photonic crystal can be arbitrarily set by introducing a substance such as water into the mesopores. It has been confirmed that it is possible to control.

  Next, the photonic crystal after the introduction of water vapor was vacuum dried again and the same measurement was repeated. As a result, the obtained spectrum agreed with the result before the introduction of water vapor. From these facts, it was found that the refractive index can be reversibly changed without changing the interval between the arrays even when the vapor adsorption and vapor desorption by vacuum drying are repeated. Therefore, it is possible to arbitrarily reversibly control the refractive index of the photonic crystal by using a substance that can be desorbed into the mesopores as a substance that can be introduced into the mesopores. confirmed.

  As described above, according to the present invention, there is provided a method for controlling the refractive index of a photonic crystal that can arbitrarily change the refractive index of the photonic crystal by a simple method without requiring a special device. It becomes possible.

  Therefore, since the refractive index control method of the photonic crystal of the present invention can arbitrarily change the refractive index of the photonic crystal by a simple method, it is suitable for the field of optical devices such as optical switches and optical modulators. It is particularly useful to apply.

It is a graph which shows the X-ray-diffraction pattern of a spherical silica type mesoporous material. It is a scanning electron microscope (SEM) photograph of a spherical silica type mesoporous material. It is a graph which shows the water vapor | steam adsorption isotherm of a spherical silica type mesoporous material. It is a scanning electron microscope (SEM) photograph (magnification 20000 times) of a photonic crystal. It is a scanning electron microscope (SEM) photograph (magnification 5000 times) of a photonic crystal. Value of the relative vapor pressure (P / P ₀₎ is a graph showing the reflection spectrum of the photonic crystal in the case of 0.25. Value of the relative vapor pressure (P / P ₀₎ is a graph showing the reflection spectrum of the photonic crystal in the case of 0.90. It is a graph which shows the relationship between the position of the peak ((lambda)) of the reflection spectrum of a photonic crystal, and the incident angle (theta) of light.

Claims (3)

A method for controlling the refractive index of a photonic crystal in which spherical silica-based mesoporous materials are arranged, wherein a detachable substance is introduced into the mesopores of the spherical silica-based mesoporous materials. A method for controlling the refractive index of a photonic crystal, wherein the refractive index of the photonic crystal is reversibly controlled by increasing or decreasing the concentration of the substance or substituting the substance with another substance .   The average particle diameter of the spherical silica-based mesoporous material is 0.01 to 3 μm, and the central pore diameter of the spherical silica-based mesoporous material is 1.8 to 5 nm. A method for controlling the refractive index of a photonic crystal according to 1. Substance detachable in the mesopores, water, photonic according to claim 1 or 2, characterized in that at least one substance selected from the group consisting of organic solvents, complex body and an organic dye A method for controlling the refractive index of a crystal.