KR102494682B1 - Optically Left-handed Nanobeads and Method for Preparing the Same - Google Patents

Abstract

In the present disclosure, in a specific frequency region (band) within the visible light-near infrared band, regardless of external environmental conditions or stimuli, electric field and magnetic field resonance phenomena can be continuously expressed and maintained simultaneously, and nanobeads can also express left-handed optical characteristics. and methods for their preparation are described.

Description

Nanobeads with left-handed optical properties and their manufacturing method {Optically Left-handed Nanobeads and Method for Preparing the Same}

The present disclosure relates to nanobeads having left-handed optical properties and a method for preparing the same. More specifically, the present disclosure provides that an electric field and a magnetic field resonance phenomenon can be continuously expressed and maintained at the same time regardless of external environmental conditions or stimuli in a specific frequency region (band) within the visible light-near infrared ray band, and left-handed optical characteristics can be expressed. It relates to nanobeads that can be used and a method for preparing the same.

Light consists of an electric field and a magnetic field, and corresponds to an electromagnetic wave having a certain wavelength. When light passes through a new medium, a phenomenon generally occurs in which the light travels according to Snell's law. In this way, unlike a general material in the natural world having a positive refractive index, when a material has a negative refractive index, a refraction phenomenon bent in a direction opposite to the direction in which light travels occurs.

All materials in the natural world are composed of atoms or molecules, and their electromagnetic properties are determined by their inherent permittivity or permeability. Most materials have positive permittivity and magnetic permeability values, so they are called DPS (Double Positive), and electric, magnetic, and phase vectors apply the right-hand rule, so they are called right-handed materials.

On the other hand, a material having a negative refractive index has a negative permittivity and negative permeability that do not exist in nature. When an artificially engineered composite exhibits a negative refractive index, it is referred to as a left-handed material. material). In other words, it means a metamaterial, which is a material having a refractive index smaller than 1, including negative numbers, among artificially manipulated composites. have a value As such, the possibility of a material having a left-handed optical property that refracts light in a direction opposite to the traveling direction of light was first proposed by Veselago (Sov. Phys. Usp. 1968, 10, 509-514), and then in 1999. In the past, it has been proven that a material having left-handed optical properties can be implemented through a split-ring resonator, and since then, a number of researchers have produced materials having left-handed optical properties in a specific frequency range. there is a bar

In general, a material having left-handed optical characteristics has a structure capable of simultaneous electric and magnetic field resonance at a specific frequency, and is designed so that a magnetic field is generated in a direction opposite to an external magnetic field (ie, has negative magnetic permeability). In order for materials to have left-handed properties in the visible-near-infrared frequency range, which accounts for more than 90% of light, the material size must be designed on a scale smaller than the wavelength of light. It is known to be able to. Recently, research on the application of metamaterials has been conducted, and an attempt to manufacture a uniform metamaterial in a large area using a lithography method for this application has been reported (ACS Nano 2012, 3, 2385).

In this regard, when metal nanoparticles are properly arranged on a two-dimensional plane, one study reported that a circular circulating current could occur (Science 2010, 328, 1135), and another study reported left-handed optical characteristics It has been reported that a strong magnetic field is formed inside a structure in which metal nanoparticles are arranged on a two-dimensional plane so as to represent (Nat. Nanotechnol. 2013, 8, 95).

However, when a left-handed material or structure is manufactured through various arrangements, the arrangement expressing left-handed optical characteristics may change due to changes in the external environment or stimuli, and in this case, it may be difficult to continuously express left-handed optical characteristics. Accordingly, the fabricated structure needs to be designed and manufactured so that left-handed optical properties can be continuously maintained regardless of external environmental changes and stimuli.

In addition, it is necessary to prepare a simpler method because a complicated process and a special device must be used to manufacture the structure. Furthermore, for commercial use, it is desirable to be able to manufacture in large quantities.

Therefore, a method for designing and manufacturing a practical left-handed material capable of amplifying electromagnetic fields in various optical frequency (or wavelength) regions is required.

In the present disclosure, it is possible not only to overcome the limitations of the prior art, but also to continuously develop and maintain electric and magnetic resonance phenomena simultaneously regardless of external environmental conditions or stimuli in a simpler manner, and to exhibit left-handed optical characteristics. It is intended to provide nanobeads and methods for preparing them.

According to the first aspect of the present disclosure,

spherical hydrogel particles;

a plurality of metal nano-colloidal particles associated with the hydrogel particle surface; and

a light-transmitting inorganic oxide nano-coating layer formed on the hydrogel particles to which the metal nano-colloidal particles are attached;

A three-dimensional structure of nanobeads having left-handed optical properties comprising

Forming a structure in which the metal nanocolloidal particles are associated with the surface of the hydrogel particles so that the nanobeads exhibit left-handed optical characteristics in a predetermined optical frequency band to simultaneously generate and amplify electric and magnetic field resonances therein,

The inorganic oxide nanocoating layer is provided with nanobeads that provide fixing force to an association structure of metal nanocolloids formed on the hydrogel particles so as to preserve left-handed optical properties.

According to an exemplary embodiment, the diameter (hydrodynamic diameter) of the hydrogel particles may be adjusted within the range of 50 to 1000 nm.

According to an exemplary embodiment, the diameter of the metal nano-colloidal particle may be adjusted within a range of 1 to 200 nm.

According to an exemplary embodiment, the distance between the metal nano-colloidal particles in the association structure may be determined within the range of 0.1 to 20 nm.

According to an exemplary embodiment, the thickness of the inorganic oxide nano-coating layer may be determined within the range of 1 to 1000 nm.

According to a second aspect of the present disclosure,

a) providing an aqueous dispersion of metal nanocolloidal particles;

b) apart from step a), providing an aqueous dispersion of spherical hydrogel particles;

c) combining the aqueous dispersion of the metal nanocolloid particles and the aqueous dispersion of the hydrogel particles under controlled temperature conditions to associate the metal nanocolloid on the hydrogel particles; and

d) forming a light-transmitting inorganic oxide nano-coating layer on the hydrogel particles in which the metal nano-colloids are associated using an inorganic oxide precursor;

A method for producing a three-dimensional structure of nanobeads having left-handed optical properties comprising

Forming a structure in which the metal nanocolloidal particles are associated with the surface of the hydrogel particles so that the nanobeads exhibit left-handed optical characteristics in a predetermined optical frequency band to simultaneously generate and amplify electric and magnetic field resonances therein,

The inorganic oxide nanocoating layer provides a method of providing a fixing force to an association structure of metal nanocolloids formed on the hydrogel particles so as to preserve left-handed optical characteristics.

According to an exemplary embodiment, in step c), the hydrogel particles and the metal nanocolloid particles are associated with each other by being attached to the surface of the hydrogel particle by electrostatic attraction, and

Due to the reversible expansion and contraction of the hydrogel particles, the association structure between the metal nanocolloid particles associated with the surface thereof and thus the distance and density between the metal nanocolloid particles may change.

The three-dimensional structure of nanobeads according to the present disclosure simultaneously induces magnetic and electric field resonance phenomena for a specific frequency band (specifically, an optical frequency of several hundred terahertz or a visible light-near infrared band), thereby exhibiting left-handed optical characteristics. It is designed. In particular, by adjusting the resonance frequency according to the internal structure or dimensions of the nanobead, it provides an advantage of amplifying energy of various optical frequencies. These characteristics can be continuously expressed without being affected by changes in the external environment. Furthermore, nanobeads can be continuously produced in a single reactor through a wet process, and a relatively simple manufacturing method is advantageous for commercial scale manufacturing.

1A and 1B respectively show the overall structure of a three-dimensional nanobead having a left-handed optical characteristic and a cross-sectional view schematically showing the inside (d is the diameter of the metal nanocolloid, s is the metal nanobead) according to an exemplary embodiment. The distance between the nanocolloids, t, is the distance from the outer surface of the metal nanocolloids to the outer surface of the nanobeads (ie, the thickness of the metal oxide nanocoating layer)),
2 is a graph showing the change in optical properties (change in spectrum) of gold nano-colloids during the process of preparing nanobeads using gold nano-colloids having a diameter of 25 nm in Example;
Figure 3 is a graph showing the optical properties according to the temperature of the aqueous dispersion solution containing nanobeads prepared using gold nanocolloids with a diameter of 25 nm in Example,
Figure 4, in the embodiment, (a) a scanning electron microscope (SEM) photograph of nanobeads prepared using gold nanocolloids having a diameter of 25 nm, (b) nanoparticles showing results closest to the experimental results of FIG. A schematic diagram of a model derived from beads through software, (c) a graph showing optical properties of nanobeads obtained through experiments and optical properties obtained through models, (d) 600 nm, 680 nm, 760 nm, and A diagram showing changes in electric and magnetic fields generated in nanobeads when irradiated with light of 800 nm, respectively;
5 shows (a, b) changes in the electric and magnetic fields generated in the nanobeads when light having a wavelength of 600 nm and (c, d) 760 nm is irradiated to the nanobeads, and the vector of the electric field and the electric field at a phase angle ( phase angle);
6 is a diagram showing directions of Poynting vectors generated in nanobeads when the nanobeads are irradiated with light having a wavelength of (a) 600 nm and (b) 760 nm;
7 is a graph showing the change in optical properties (change in spectrum) of gold nano-colloids during the process of preparing nanobeads using gold nano-colloids having a diameter of 40 nm in Example;
8 is a graph showing optical properties according to temperature of an aqueous dispersion solution containing nanobeads prepared using gold nanocolloids having a diameter of 40 nm in Example, and
9 is an example, (a) a scanning electron microscope (SEM) photograph of nanobeads prepared using gold nanocolloids having a diameter of 40 nm, (b) nanoparticles showing results closest to the experimental results of FIG. 7 . A schematic diagram of the model derived from the beads through software, (c) a graph showing the optical properties of the nanobeads obtained through the experiment and the optical properties obtained through the model, (d) the light of 570 nm, 760 nm, and 870 nm in the model A diagram showing changes in the electric and magnetic fields generated in the nanobeads when each is irradiated, (e) when the nanobeads are irradiated with light having a wavelength of 870 nm, the changes in the electric and magnetic fields generated in the nanobeads, and the electric and electric fields A diagram showing a vector according to a phase angle, and (f) a diagram showing the direction of a pointing vector generated in a nanobead when light having a wavelength of 870 nm is irradiated to the nanobead.

The present invention can all be achieved by the following description. The following description should be understood as describing preferred embodiments of the present invention, but the present invention is not necessarily limited thereto. In addition, the accompanying drawings are for understanding, and the present invention is not limited thereto, and details of individual components can be properly understood by the specific purpose of the related description to be described later.

Terms used in this specification may be defined as follows.

"Hydrogel" is also called "hydrogel" and can refer to a three-dimensional, hydrophilic or amphiphilic polymer network capable of absorbing large amounts of water, usually as a cross-linked polymer of hydrophilic monomers. These polymer networks can be homopolymers or copolymers and can phase separate from the aqueous medium due to the presence of covalent chemical or physical (ionic, hydrophobic interactions, entanglement, etc.) cross-links. However, polymer chains other than the crosslinking point can contract or expand the structure of the chain depending on the degree of affinity with water or aqueous solution, and as a result, the hydrogel can swell and contract in the polymer and aqueous medium.

“Nanoscale” can broadly mean that the largest dimension of a feature is on the nanometer scale, for example in the range of about 0.1 to 1000 nm, specifically about 1 to 700 nm.

“Soft” means capable of reversibly deforming (eg, expanding or contracting) in a manner that does not damage or break at a given strain level (eg, from about 1 to 1000%, specifically from about 10 to 500%). It can be understood to mean the properties of the material.

"External stimulus responsiveness" may be understood to mean a property that exhibits behavior (eg, reversibly changing behavior) depending on external stimuli, including temperature.

"Surface plasmon" may refer to a phenomenon in which electrons collectively and regularly oscillate with a regular frequency due to a charging phenomenon when a conductive particle forms an interface with a dielectric material. there is. At this time, the vibration period is changed not only by the geometric shape of the particle but also by the association structure of the particle, and accordingly, when a specific wavelength or period of light coincides with the vibration period, a specific wavelength of light may be scattered by the particle or structure.

"LCST (low critical solution temperature)" is the maximum temperature at which a polymer can be dissolved in a solvent in a broad sense, and in a narrow sense, it may mean the temperature at which a polymer constituting a hydrogel loses solubility in an aqueous medium. .

"Contacting" narrowly means direct contact between two objects, but in a broad sense it can be understood that any additional component may be intervened.

It can be understood that the expressions "on" and "above" are used to refer to the concept of relative position. Therefore, not only when other components or layers are directly present in the mentioned layers, other layers (intermediate layers) or components may be interposed or present therebetween. Similarly, the expressions “under”, “under” and “below” and “between” may also be understood as relative concepts of position. In addition, the expression “sequentially” may also be understood as a relative positional concept.

In this specification, when it is said that a certain component is "included", it means that it may further include other components and / or steps unless otherwise stated.

Nanobeads with left-handed optical properties

Nanobeads (specifically, nanobeads having a three-dimensional structure) according to one embodiment of the present disclosure exhibit simultaneous electric and magnetic resonance phenomena in a specific optical frequency band, specifically several hundred terahertz optical frequency (visible light-near infrared ray) band, Left-handed optical characteristics can be exhibited. In this regard, FIGS. 1A and 1B each schematically show the overall structure and internal cross-section of a 3D nanobead 100 having left-handed optical characteristics.

Referring to the drawing, the nanobeads 100 include largely spherical hydrogel particles 101, a plurality of metal nanocolloidal particles 102, and an inorganic oxide coating layer (or glass window) 103.

In this regard, the hydrogel particles 101 may provide a position (plane) or space at which the metal nanocolloid 102 can induce an association structure capable of expressing left-handed optical characteristics. In particular, since the hydrogel particles 101 exhibit sensitivity to external environments or stimuli and have a soft property that can change in size, close packing of metal nanocolloids can be maximized.

- hydrogel particles (101)

According to the illustrated embodiment, the diameter (hydrodynamic diameter) of the hydrogel particles 101 can be determined in consideration of the size of metal nanocolloids, the number of associations, the size of nanobeads to be produced, etc., for example, about 50 to 1000 nm, specifically about 75 to 700 nm, and more specifically about 100 to 500 nm. However, the size range of the above-described hydrogel particles can be understood as an example.

In this regard, the material of the hydrogel may be a soft material, specifically a material having characteristics of being reversibly deformed (eg, contraction or expansion) in response to an external stimulus. Illustratively, the hydrogel may be a polymer, and its material is, for example, poly(N-isopropylacrylamide) [poly(N-isopropylacrylamide), pNIPAM], poly(N-isopropyl acrylamide-co -Allylamine) [poly(N-isopropyl acrylamide-co-allylamine), poly(NIPAM-co-AA)], poly(N-isopropyl acrylamide-co-2-(dimethylamino)ethyl methacrylate)[ poly(Nisopropylacrylamide-co-2-(dimethylamino)ethyl methacrylate), poly(NIPAM-co-DMAEMA)], poly(N-isopropylacrylamide-co-2-(dimethylamino)ethyl acrylate)[poly(N -isopropyl acrylamide-co-2-(dimethylamino)ethyl acrylate), poly(NIPAM-co-DMAEA)], poly(N-isopropyl acrylamide-co-acrylic acid)[poly(N-isopropyl acrylamide-co-acrylic acid ), poly(NIPAM-co-AAc)], poly(N-isopropyl acrylamide-co-methacrylic acid) [poly(N-isopropyl acrylamide-co-methacrylic acid), poly(NIPAM-co-MAAc)], poly(N,N-diethylacrylamide), poly(N-vinylcaprolactam), poly(ethylene glycol) )], and at least one selected from the group consisting of poly(ethylene glycol-b-propylene glycol-b-ethylene glycol) [poly(ethylene glycol-b-propylene glycol-b-ethylene glycol)].

Illustratively, the hydrogel may be a polymer having a lower critical solution temperature (LCST), and the LCST of the hydrogel is, for example, about 0 to 100 ° C, specifically about 10 to 70 ° C, more specifically about 25 to 50 °C.

- Metal nano colloid (102)

In the illustrated embodiment, the metal nanocolloid 102 is an essential element for the nanobeads 100 to exhibit left-handed optical properties, and an association structure between the metal nanocolloids 102 formed on the surface of the hydrogel particle 101 is formed. .

In this way, by designing the hydrogel particle 101 to form an association structure of the metal nanocolloid 102, left-handed optical characteristics can be expressed in a specific frequency band. Specifically, since the resonant frequency can be changed by adjusting the internal structure such as the overall structure and individual components of the hydrogel particles 101 and the metal nanocolloid 102 of the nanobeads 100, the electric and magnetic field resonance phenomena It can amplify the energy of various optical frequency bands by using.

According to an exemplary embodiment, the metal nanocolloid 102 may have at least one shape selected from the group consisting of sphere, rod, wire, pyramid, cube, and prism. More specifically, It may have a spherical shape. At this time, the diameter (d) of the individual metal nanocolloids 102 forming the association structure is, for example, about 1 to 200 nm, specifically about 5 to 150 nm, more specifically about 10 to 100 nm, particularly specifically It may be determined or adjusted in consideration of a desired resonant frequency band in the range of about 20 to 50 nm. In addition, the interval (s) between the metal nano-colloidal particles 102 in the association structure is, for example, about 0.1 to 20 nm, specifically about 0.5 to 10 nm, more specifically about 1 to 5 nm within the target range. It can be appropriately adjusted in consideration of the resonant frequency band.

According to an exemplary embodiment, the ratio of the diameter of the metal nanocolloid particle to the diameter of the hydrogel particle (hydrodynamic diameter) can be determined in consideration of the aperture of the metal colloid used and the optical properties required for the nanobead, For example, 1: about 2 to 1000, specifically 1: about 5 to 100, more specifically 1: adjustable in the range of about 10 to 50.

According to an exemplary embodiment, the material of the metal nanocolloid may be at least one selected from among gold, silver, platinum, palladium, copper, and aluminum. According to a specific embodiment, the material of the metal nanocolloid may be gold (Au) and/or silver (Ag), particularly gold (Au).

- Light-transmitting inorganic oxide nano-coating layer (103)

According to the illustrated embodiment, the inorganic oxide nano-coating layer (or nano-glass window) may (i) suppress left-handed optical characteristics from being damaged or altered by various external environments and/or stimuli of the nanobead structure, thereby improving left-handed optical characteristics. It can provide a fixing force to the association structure of metal nanocolloids formed on the hydrogel particles so that it can be preserved, and at the same time, it allows the nanobeads to be stably dispersed in various dispersion environments, (ii) the size varies depending on the external environment. It performs the function of preserving the left-handed optical properties of the three-dimensional structure based on the metal nanocolloidal association structure by fixing the structure of the spherical hydrogel particles that can change.

Particularly noteworthy is that the metal nanocolloid structure formed on the hydrogel particles can be induced to have a more dense association structure through the inorganic oxide coating.

According to an exemplary embodiment, the inorganic oxide nano-coating layer may be made of at least one material selected from the group consisting of silica, alumina, titania, zinc oxide, and the like, specifically a silica material. The thickness of the inorganic oxide nanocoating layer may be, for example, about 1 to 1000 nm, specifically about 2 to 500 nm, more specifically about 3 to 100 nm, and particularly specifically about 5 to 20 nm. . According to an exemplary embodiment, the ratio of the thickness of the inorganic oxide nanocoating layer to the hydrogel diameter (hydrodynamic diameter) may be determined in consideration of the characteristics and uses of the nanobeads, for example, 1: about 0.5 to 500; Specifically, 1: about 5 to 200, more specifically 1: may be adjusted in the range of about 10 to 50.

In an exemplary embodiment, as described above, the hydrogel particles 101, the plurality of metal nanocolloids 102 associated on the surface of the hydrogel particles, and the nanobeads 100 provided with the inorganic oxide nanocoating layer 103 The diameter can be adjusted in consideration of the optical characteristics of the nanobeads, the size of the metal nanocolloid, the size of the hydrogel, etc., for example, about 100 to 1500 nm, specifically about 150 to 1000 nm, more specifically about 200 nm. to 500 nm.

The structure and function of the nanobead having left-handed optical characteristics according to one embodiment of the present disclosure will be described in more detail as follows.

The metal nanocolloidal particles 102 in the nanobeads 100 have a characteristic of collective oscillation of free electrons in the nanocolloid through a localized surface plasmon resonance (LSPR) phenomenon. At this time, when vibrating collectively, it is known that the vibration frequency is different depending on the element, size and / or shape of the metal nanocolloid, in particular, the element constituting the metal nanocolloid is gold (Au) and / or silver (Ag). In this case, it may have a vibration frequency in the visible light-near infrared band. When the frequency of light coincides with the frequency of the association structure of the metal nanocolloid 102, a resonance phenomenon occurs, and as a result, the electromagnetic field of the metal nanocolloid is amplified.

In an exemplary embodiment, when the metal nanocolloid 102 has a spherical shape, as the diameter of the particle (indicated by d in FIG. 1) increases, the resonance frequency moves toward a longer wavelength, while the metal nano Depending on the association structure between colloids, the resonant frequency and/or its range also changes. Accordingly, the degree of amplification of the electromagnetic field may be changed.

In order to form an inductance (L)-capacitance (C) circuit in a specific object, a circular current and electric field for forming an inductance circuit can be generated, such as a split-ring resonator. It is necessary to have a structure such as a ring or a coil, and it is possible to have a structure such as a capacitor capable of generating a displacement current generated when forming a capacitor circuit or a magnetic field caused by it. The nanobead structure simultaneously resonates and amplifies electric and magnetic field components at a specific frequency/wavelength, forms a circular current and electric field, and generates a magnetic field due to a cyclic displacement current when forming a capacitor circuit to form an L-C circuit. be able to At this time, the factors that change the characteristics (electric field and magnetic field values) of the L-C circuit may be mainly the characteristics and association structure of the metal nanocolloid. As such, the L-C circuit characteristics of the nanobeads can be changed by adjusting various factors including the spacing between the metal nanocolloids 102 included in the nanobeads 100 (indicated by s in FIG. 1) and the diameter of the metal nanocolloids. . In this regard, considering various characteristics of the nanobeads, including the target resonance frequency band, the interval (s) between the metal nanocolloidal particles 102 in the nanobeads is, for example, about 0.1 to 20 nm, specifically about 0.5 nm. to 10 nm, more specifically within the range of about 1 to 5 nm. In addition, the diameter (d) of the metal nanocolloid 102 may be determined or adjusted in the range of, for example, about 1 to 200 nm, specifically about 5 to 150 nm, and more specifically about 10 to 100 nm.

As described above, when an artificial magnetic structure that reacts to an externally applied magnetic field is formed due to the arrangement of metal nanocolloids, which are non-magnetic materials, the metal nanocolloid or a structure formed therefrom is formed at a specific wavelength. When the nanobeads have a negative permittivity and the effective permeability is controlled to have a negative value, the structure may be expressed as a negative refractive index. In this regard, as one of the methods for confirming whether or not the nanobead can refract light of a specific wavelength in the direction opposite to the direction of incidence, it can be exemplified by observing and determining the change in the pointing vector. The Poynting vector represents the direction of propagation of the electromagnetic wave along with the energy density of the electromagnetic wave. Therefore, the presence or absence of left-handed optical characteristics can be confirmed from the information on the direction of the Poynting vector of light having a specific wavelength and the direction of the Poynting vector formed in the nanobeads. For example, when light having a specific wavelength is incident and the direction of the Poynting vector generated from the nanobeads is directed to an incident point opposite to the incident direction of the light, the refractive index of the nanobeads may have a negative value.

As described above, the spherical hydrogel particles 101 provide a space in which the metal nanocolloid 102 can form a structure capable of simultaneously exhibiting electric and magnetic field amplification phenomena. In this regard, the metal nanocolloid 102 may be adsorbed (or fixed/attached) on the surface of the hydrogel particle through various means such as electrostatic attraction. As an example, the hydrogel particles 101 and the metal nanocolloids 102 are easily adsorbed when they have opposite surface charges, and at this time, the adsorbed plurality of metal nanocolloids 102 have a predetermined It has an inter-particle spacing (s). In addition, if necessary, the association rate may be increased by controlling the temperature (eg, elevated temperature conditions) during the combination between the hydrogel particles and the metal nanocolloid.

According to the present embodiment, as the distance between the metal nanocolloid particles becomes narrower overall, not only the electric field resonance and amplification phenomenon of the nanobead structure increase, but also the electromagnetic field resonance strong enough to form an L-C circuit at a specific optical frequency (wavelength). The phenomenon can be expressed inside the nanobead structure. At this time, as the size of the particles of the metal nanocolloid used increases, the optical frequency at which the electromagnetic field resonance phenomenon is expressed decreases (or the wavelength increases). Therefore, the resonance frequency of the L-C circuit expressed in the nanobeads can be selected. As an example, when gold nanocolloids are used as metal nanocolloids, resonance frequencies are formed in the visible light-near infrared region. ) can be adjusted. In this regard, the light irradiated onto the nanobeads is light in the visible light-infrared band, for example, about 400 to 2500 nm, specifically about 500 to 2000 nm, more specifically about 600 to 1400 nm, for example. It may be light selected from a wavelength band.

In an exemplary embodiment, the material of the hydrogel particles 101 may be a soft material having external stimulus response as described above, when it is brought into contact with an aqueous medium (or aqueous solution) (eg For example, when put into an aqueous medium), as the temperature increases, the hydrogel particles 101 may exhibit contraction characteristics, and as a result, the metal nanocolloid 102 may be designed to have a more dense structure. In addition, when stress is applied from the outside due to the nature of the hydrogel itself (for example, when pressure is applied during the silica coating process as described later), it can shrink in response to the pressure.

However, at the same time as the above-described response behavior, since the size of the hydrogel particles sensitively changes depending on the temperature of the external aqueous medium in contact with them, the characteristics of the solution, and external stimuli, the association structure of the metal nanocolloids changes, and as a result, the nanobeads The left-handed optical characteristics are greatly affected by the external environment. Therefore, left-handed optical characteristics can be implemented only when certain external conditions are continuously maintained.

Moreover, even if a specific external condition is continuously maintained, there is a possibility that a metal nanocolloid-based structure continuously contacts another metal nanocolloid-based structure to cause aggregation or structural deformation during long-term storage. As such, there is a need for a coating capable of continuously maintaining the structure in which the metal nanocolloid associative structure is formed without being affected by the external stimulation environment and/or the state (or condition) of the medium.

Under the above background, the nanocoating layer (or glass window; 103) of an inorganic oxide material such as a metal or metalloid oxide (eg, silica) protects the metal nanocolloid-based structure from various external environments and / or stimuli, It can function to stably disperse nanobeads in various dispersion environments (mediums). Furthermore, the inorganic oxide nanocoating layer 103 immobilizes the hydrogel particle structure whose size can change depending on the external environment, so that the left-handed optical characteristics of the metal nanocolloid structure can be continuously preserved regardless of the external environment change. In short, the inorganic oxide nano-coating layer 103 can provide a function that enables the metal nano-colloidal structure to stably implement left-handed optical characteristics in various environments.

According to the illustrated embodiment, the inorganic oxide nanocoating layer has a light transmittance, so that the irradiated (incident) light is transmitted without loss to the inside of the structure, so that the metal nanocolloid structure can exhibit high electric and magnetic field resonance at the same time (Fig. 1 through t). Specifically, the coating material may be required to exhibit transparency in the visible light-near infrared region. In this regard, when an inorganic oxide precursor is used in forming the coating, the thickness of the inorganic oxide nano-coating layer may be adjusted by adjusting the concentration and/or treatment time of the precursor.

In addition, it is noteworthy that the inorganic oxide nanocoating layer can induce a plurality of metal nanocolloids to have a more dense association structure on the hydrogel particles. Therefore, the inorganic oxide nanocoating layer serves to further clarify left-handed optical characteristics while the nanobeads stably exhibit left-handed optical characteristics.

Manufacturing method of nanobeads with left-handed optical properties

According to another embodiment of the present disclosure, a method of manufacturing a three-dimensional structured nanobead having left-handed optical properties is provided. In this regard, a characteristic part is that nanobeads can be prepared through a wet method in consideration of commercial factors. Specifically, since the step of assembling metal nanocolloids and the step of forming a silica nano-coating layer for forming the final nanobead structure can be continuously performed in a single reactor, and the process is relatively simple, it can be manufactured on a variety of scales depending on the purpose, etc. can

On the other hand, a method of manufacturing a 3D nanobead structure having left-handed optical properties is not limited to a specific method, but may be implemented in the following exemplary method:

First, metal nanocolloid (specifically, nanocolloid of a metal selected from at least one of gold, silver, platinum, palladium, copper, and aluminum) particles are dispersed in an aqueous medium.

According to an exemplary embodiment, a metal precursor (typically, a metal salt) is combined (introduced) in an aqueous medium in the presence of a reducing agent, and metal ions are reduced to synthesize a nanoscale metal colloid (ie, a metal nanocolloid). can do. As an example, a process of mixing a metal precursor solution with a solution (specifically, an aqueous solution) in which a reducing agent is dissolved may be involved.

According to an exemplary embodiment, when the material of the metal nanocolloid is gold (Au), the gold precursor is typically a form containing Au(III) ions, and may be, for example, a form of gold (III) chloride. As an example, the gold precursor may be one or two or more selected from the group consisting of HAuCl ₄ , AuCl, AuCl ₂ , AuCl ₃ , Na ₂ Au ₂ Cl ₈ , NaAuCl ₂ , and hydrates thereof, and more specifically, HAuCl can be ₄ In addition, as the reducing agent, at least one selected from citrate (specifically, tri-sodium citrate, mono-sodium citrate, potassium citrate, etc.), ascorbic acid, alcohol, and other reducing agents may be used. According to certain embodiments, the reducing agent may be tri-sodium citrate.

In the above embodiment, the concentration of the metal precursor aqueous solution may be adjusted within the range of, for example, about 0.01 to 10 mM, specifically about 0.1 to 5 mM, and more specifically about 0.25 to 1.5 mM. In addition, the concentration of the reducing agent aqueous solution may be adjusted within the range of, for example, about 0.1 to 7 mM, specifically about 0.5 to 5 mM, and more specifically about 0.8 to 2.5 mM.

According to exemplary embodiments, the molar ratio of reducing agent to metal precursor in the combination is, for example, in the range of about 1 to 500:1, specifically about 3 to 450:1, more specifically about 25 to 400:1. Since it can be controlled in, the combination ratio between the metal precursor aqueous solution and the reducing agent aqueous solution can be adjusted in consideration of this.

According to exemplary embodiments, the reduction reaction of the metal precursor solution may be performed at, for example, about 85 to 150 ° C, specifically about 90 to 135 ° C, more specifically about 95 to 105 ° C, and the reaction time is, For example, it is adjustable within the range of about 10 minutes to 5 hours, specifically about 20 minutes to 3 hours, and more specifically about 30 minutes to 1 hour 30 minutes. In addition, the above-described reduction reaction step may be repeated at least one more time in order to adjust the size and the like of the metal nanocolloid.

Thereafter, the reaction product may be subjected to a conventional post-treatment, for example, a purification treatment step. The metal nanocolloid prepared in this way may form an aqueous dispersion to be attached on the hydrogel particles in a subsequent step, wherein the aqueous dispersion is a stabilizer (e.g., , tri-sodium citrate). According to an exemplary embodiment, the concentration of the metal nanocolloidal particle dispersion (aqueous dispersion) is, for example, about 0.001 to 0.3% by weight, specifically about 0.005 to 0.15% by weight, more specifically about 0.01 to 0.1% by weight. range can be

On the other hand, since the aqueous dispersion of spherical hydrogel particles can be prepared separately from the step of providing the metal nanocolloid, technical details regarding the material thereof have been described above, and overlapping descriptions will be omitted. However, the hydrogel particles in the aqueous dispersion may be designed to have a uniform size as much as possible. At this time, "uniform size" is, for example, about ± 35% or less, specifically about ± 30% or less, more specifically about ± 25% or less, particularly about about ± 25% or less, particularly about the desired size of the hydrogel particles. It may mean that it may be less than or equal to ±20%, and may further mean that it may be less than or equal to about ±15% or less than or equal to about ±10%. In addition, the concentration of the aqueous dispersion of the hydrogel particles may be, for example, about 0.01 to 10% by weight, specifically about 0.05 to 5% by weight, more specifically about 0.1 to 3% by weight, but this is for illustrative purposes only. can be understood

Next, a step of combining or contacting the aqueous dispersion of the metal nanocolloid particles and the aqueous dispersion of the hydrogel particles under a controlled temperature condition is performed, so that the metal nanocolloids can be assembled on the hydrogel particles. According to an exemplary embodiment, the metal nanocolloidal particles may be attached to the surface of the hydrogel particles by electrostatic attraction.

According to an exemplary embodiment, the surface charge of the hydrogel particle may be prepared to have a positive charge by using a polymer containing a monomer capable of inducing a positive charge on the surface of the hydrogel particle. On the other hand, when the metal nanocolloid particles have a positive surface charge, the hydrogel particles use a polymer containing a monomer capable of inducing a negative charge on the surface, so that the surface charge of the hydrogel particles has a negative charge. can be manufactured. As such, since the metal nanocolloid particles and the hydrogel particles have opposite surface charges, the hydrogel particles and the metal nanocolloid may be attached and associated with each other due to strong electrostatic attraction.

According to a specific embodiment, the hydrogel may typically be in a positively charged state, illustratively, the zeta potential (30 ° C.) of the hydrogel polymer is in the range of about 5 to 40 mV, specifically about 10 to 30 mV. On the other hand, the zeta potential (30° C.) of the metal nanocolloidal particles is, for example, about -70 to -10 mV (specifically, about -55 to -35 mV) and about -50 to -5 mV (specifically, about -50 to -5 mV). about -35 to -20 mV), but this is understood as an example and may be changed depending on the components of individual elements and the like.

Meanwhile, the temperature at which the metal nanocolloid particles are attached or associated with the hydrogel particle surface may be, for example, about 0 to 100 °C, specifically about 10 to 70 °C, and more specifically about 25 to 60 °C. In addition, the attachment time is not particularly limited, but may be adjusted within the range of, for example, about 10 minutes to 48 hours, specifically about 25 minutes to 24 hours, and more specifically about 30 minutes to 12 hours.

In this regard, the diameter of the hydrogel particles may change due to reversible expansion and contraction according to the combination temperature of the aqueous dispersion of the metal nanocolloidal particles. Due to the reversible expansion and contraction of the hydrogel particles, the association structure between the metal nanocolloid particles associated with the surface thereof and thus the distance and density between the metal nanocolloid particles may change.

According to an exemplary embodiment, the dispersion stabilizer that can be contained in the metal nano-colloidal dispersion (water dispersion) can be introduced in an appropriate amount in consideration of the size of the target metal nano-colloidal particle. Illustratively, the concentration of the dispersion stabilizer in the metal nanocolloidal dispersion (water dispersion) is, for example, about 0.1 to 2 mM, specifically about 0.3 to 1.5 mM, more specifically about 0.5 to 1 mM. It can be. Also, the combining step may be conducted under stirring conditions.

According to an exemplary embodiment, the density of the metal nanocolloid particles attached to the hydrogel particles can be adjusted by adjusting the concentration of the metal nanocolloid and the hydrogel particles contained in the dispersion (eg, metal It can be controlled by adjusting the amount of hydrogel particles to be combined (injected) while keeping the concentration of the aqueous dispersion of nanocolloids constant). In this regard, the concentration of the metal nanocolloid aqueous dispersion can be controlled from the extinction intensity or extinction value of a peak of a specific metal nanocolloid in the ultraviolet-visible-near-infrared (UV-VIS-NIR) spectral spectrum. . It is based on the Beer-Lambert law, which states that spectral intensity is linearly proportional to concentration. Accordingly, the concentration of the aqueous dispersion of the specific metal nanocolloid can be maintained at a predetermined concentration by making the specific peak extinction value expressed from the metal nanocolloid constant in the spectral spectrum. On the other hand, the concentration of the hydrogel particles included in the aqueous dispersion of hydrogel particles can be adjusted, for example, by changing the input amount of the particle dispersion redispersed in water (eg, deionized water) after particle synthesis.

As described above, when a plurality of metal nanocolloids form an association structure (eg, a two-dimensional association structure) and are attached to the surface of the hydrogel particle, the nanobeads are stable without being affected by the external environment and / or stimuli. A step of forming a light-transmitting inorganic oxide nano-coating layer (specifically, a silica nano-coating layer) may be performed to provide a fixing force to retain left-handed optical characteristics and/or to enhance left-handed optical characteristics.

As described above, the material of the inorganic oxide nano-coating layer may be at least one selected from the group consisting of silica, alumina, titania, zinc oxide, and the like, and in specific embodiments, the inorganic oxide nano-coating layer may be made of silica. As such, in order to form the inorganic oxide nano-coating layer, coating may be performed using a precursor thereof.

According to an exemplary embodiment, when the inorganic oxide is silica, the precursor thereof is typically a silane-based compound, such as mercaptopropyl trimethoxysilane (MPTMS), tetraethyl orthosilicate (TEOS), trimethoxy orthosilicate (TMOS), GPTMS ((3- glycidoxypropyl)methyldiethoxysilane), GOTMS (γ-glycidyloxypropyl trimethoxysilane), APTMOS (aminophenyl trimethoxysilane), and APTES (aminopropyl triethoxysilane) may be at least one selected from the group consisting of.

In this regard, the silica nano-coating layer may be formed using a method known in the art. As an example, the silica nano-coating layer may be formed through a method applicable on a commercial scale, such as a Stober method or a modified Stober method. In this regard, the stover method is disclosed in W. Stöber, A. Fink, E. Bohn, J. Colloid Interface Sci., 1968, 26, 62. The document is incorporated as a reference for the present disclosure. included The stover method is typically a method in which a reaction mixture containing a silane compound (eg, TEOS, MPTMS, etc.) as a silica precursor, water, and a basic component is carried out under mild temperature and relatively high pH conditions. At this time, the entire reaction involved may be represented by the following Reaction Formula 1 (for example, when TEOS is used as a silane compound as a precursor).

[Scheme 1]

Si(OC ₂ H ₅ ) ₄ + 2H ₂ O ↔ SiO ₂ + 4C ₂ H ₅ OH

According to an exemplary embodiment, when MPTMS is used as a silica precursor, methanol is produced instead of ethanol as a by-product during the hydrolysis process according to Scheme 1 above. Since MPTMS has a thiol (-SH) functional group, Au-S bonding is possible when metal nanocolloids, especially gold nanocolloids, arranged on the surface of hydrogel particles are used. When the silane compound is subjected to condensation and curing of the colloidal-hydrogel particle structure, nanobeads coated with silica can be prepared.

Alternatively, when the modified Stover method is applied, the basic principle of the Stover method is used, but when the surface of the hydrogel particles lacks -OH groups, a silane coupling agent (or surface primer) is used to It may involve providing silanol anchor groups to the surface.

According to a specific embodiment, when the inorganic oxide nano-coating layer is formed of a silica material, a silane compound may be used as a precursor, and the silane compound and a base component are injected together into a reactor to prepare previously prepared composite particles (on hydrogel particles). A structure in which a plurality of metal nano-colloidal particles are associated) may be subjected to silica nano-coating. Illustratively, the basic component may be at least one selected from ammonium hydroxide, sodium hydroxide, potassium hydroxide, and the like, and more specifically, may be ammonium hydroxide.

In this regard, the silica precursor may be introduced into the reactor in the form of an aqueous solution, the concentration thereof being, for example, about 0.01 to 50 mM, specifically about 0.1 to 30 mM, more specifically about 1 to 20 mM. can be regulated. In addition, the basic component may also be introduced in the form of an aqueous solution, wherein the concentration of the aqueous solution of the basic component is, for example, about 0.01 to 5% (w / w), specifically about 0.05 to 2% (w / w), More specifically, it is controllable within the range of about 0.1 to 0.5% (w/w).

According to an exemplary embodiment, about 10 minutes to 48 hours (specifically about 25 minutes to 24 hours, more specifically about 25 to 60 ℃) at a temperature of about 0 to 100 ℃ (specifically about 10 to 70 ℃, more specifically about 25 to 60 ℃) Specifically, by reacting for about 30 minutes to 12 hours), an inorganic oxide nano-coating layer may be formed.

However, in addition to the above-described silane compound as a silica precursor, various coating materials capable of preserving the left-handed optical properties of the metal nanocolloid structure and expressing the left-handed optical properties under various environmental and/or dispersion conditions may be used.

As an example, the inorganic oxide nano-coating layer may be made of alumina. In this case, the alumina precursor may be, for example, an organic or inorganic acid salt of aluminum, an alkoxide, a complex, or a combination thereof, and more specifically, aluminum acetate or aluminum acetyl. acetonate, aluminum bromide, aluminum t-butoxide, aluminum sec-butoxide, aluminum pentoxide, aluminum ethoxide, aluminum isopropoxide, aluminum tributoxide, aluminum chloride, aluminum bromide, aluminum iodide, aluminum sulfate, It may be at least one selected from the group consisting of aluminum nitrate and hydrates thereof. In addition, the inorganic oxide nanocoating layer may be made of titania, and the titania precursor may be, for example, at least one selected from titanium trichloride, titanium tetrachloride, titanium isopropoxide, and titanium butoxide. In addition, when the inorganic oxide nano-coating layer is made of zinc oxide, the precursor is selected from, for example, zinc nitrate, zinc sulfate, zinc acetate, zinc formate, zinc (II) chloride, zinc iodide, zinc acetylacetonate, and hydrates thereof can be at least one.

In this way, when the inorganic oxide nano-coating layer is formed with a material other than silica, the coating process is performed using a known inorganic oxide formation mechanism in the art (eg, a sol-gel method, a reduction method (thermal reduction method or chemical reduction method) Since it can be performed, details thereof will be omitted.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention, but the following examples are provided to more easily understand the present invention, but the present invention is not limited thereto.

Example

Preparation of gold nanocolloids

In this example, gold (Au) was used to form metal nanocolloids, and two types of gold nanocolloids having diameters or apertures ( d indicated in FIG. 1 ) of 25 nm and 40 nm, respectively, were prepared for this experiment.

Gold nanocolloids having diameters of 25 nm and 40 nm, respectively, were prepared by referring to prior literature ( Langmuir, 2011, 27, 11098-11105). As a first step, 150 mL of a 2.2 mM aqueous solution of tri-sodium citrate was heated to 105 °C, and after forming thermal equilibrium for 15 minutes, a 1 mL aqueous solution of 25 mM HAuCl ₄ 3H ₂ O was added to an aqueous solution of tri-sodium citrate. and reacted for 30 minutes. Thereafter, the temperature was lowered to 95 °C to form an equilibrium, and then a 25 mM HAuCl ₄ .3H ₂ O 1 mL aqueous solution was introduced and the reaction was performed for 30 minutes. In addition, the process of reacting for 30 minutes by adding 1 mL of 25 mM HAuCl ₄ .3H ₂ O aqueous solution was repeated once more. In the second step, after taking out 55 mL of the reactant, 55 mL of a 2.2 mM tri-sodium citrate aqueous solution was added to the reactant to dilute it, and 25 mM HAuCl ₄ 3H ₂ O 1 mL aqueous solution was additionally added to increase the reaction to 30 mL. The procedure performed for 3 minutes was repeated 3 times. After each step was completed, the diameter was checked, and if the particles grew to 25 nm or 40 nm, the following purification process was performed. Otherwise, the second step was repeated.

Preparation of hydrogel spherical particles

Hydrogel spherical particles were heated to 80 °C in a 250 mL round flask with 100 mL of an aqueous solution containing 0.08 g N , N′ -methylene bis(acrylamide) and 1 g N-isopropylacrylamide, and thermally Equilibrium was established. Thereafter, 70 μL of allylamine and 2 mL of potassium persulfate aqueous solution (0.025 g/mL) were continuously added to perform the reaction.

Preparation of nanobeads containing 25 nm gold nanocolloid (Example 1)

After the previously prepared gold nanocolloid and hydrogel spherical particles were centrifuged, the supernatant was removed. After removing the supernatant, the gold nanocolloids were redispersed in an aqueous solution of tri-sodium citrate, and the spherical hydrogel particles were redispersed in ultrapure water. In the tri-sodium citrate aqueous solution in which gold nanocolloids were dispersed, the concentration of trisodium citrate was varied depending on the diameter of the gold nanocolloids. In the case of gold nanocolloids with a diameter of 25 nm, 0.88 mM of trisodium It was dispersed using an aqueous citrate solution. After putting 100 mL of an aqueous solution in which gold nanocolloids having a diameter of 25 nm were dispersed into the reactor, 0.175 mL of an aqueous solution in which spherical hydrogel particles were dispersed was added and stirred. The reactor was stored at 4 °C for approximately 45 minutes, and then placed in a heating chamber at 53 °C for 45 to 60 minutes to arrange gold nanocolloids on the surface of the hydrogel spherical particles. Thereafter, the reactor was cooled to room temperature and stored for 45 minutes.

Then, equilibrium was formed at 50 ° C. for 15 minutes, followed by stirring, and 25 mL of 17.9 mM mercaptopropyl trimethoxysilane (MPTMS) aqueous solution and 0.5 mL of 28% NH ₄ OH were sequentially introduced into the reactor. And a process of forming a silica nano-coating layer was performed at 50 ° C. for 5 hours. Since the thickness of the silica nanocoating layer varied depending on the reaction time and the concentration of the silane compound used, the concentrations of the gold nanocolloid and hydrogel spherical particles used were adjusted according to the final structure of the nanobeads on which the gold nanocolloid structure was formed. The concentration of the gold nanocolloid used in this example was adjusted so that the extinction value at 525 nm in the ultraviolet-visible-near-infrared spectrum was 0.96.

After completion of the reaction, the prepared nanobeads were centrifuged to remove the supernatant, then repeatedly purified, and finally dispersed in ultrapure water.

Preparation of nanobeads containing 40 nm gold nanocolloid (Example 2)

In preparing nanobeads including 40 nm diameter gold nanoparticles, since the diameters of the gold nanocolloids used are different, the concentration of the tri-sodium citrate aqueous solution used to disperse the gold nanocolloids and the nanobeads The experimental procedure was entirely the same as in Example 1, except that the amount of the dispersion containing the gold nanocolloid and hydrogel spherical particles used was changed.

Specifically, a 0.92 mM tri-sodium citrate aqueous solution was used to disperse gold nanocolloids, and the concentration of gold nanocolloids was adjusted so that the extinction value at 527 nm was 0.96 in the ultraviolet-visible-near-infrared spectrum. , At this time, 0.106 mL of the aqueous solution in which the hydrogel spherical particles were dispersed was added to the aqueous gold nanocolloid solution.

Characterization of nanobeads

The optical properties of the prepared nanobeads were analyzed using an ultraviolet-visible-infrared spectrometer (V-670, JASCO, Japan).

The size of the hydrogel spherical particles was determined by measuring the hydrodynamic diameter using dynamic light scattering (Zetasizer Nano ZS90, Malvern Instrument, UK), which was 343 nm at room temperature and 155 nm at 50 °C.

The structure of the nanobeads was observed using a scanning electron microscope (Hitachi S-4800, Hitachi, Japan). Electric and magnetic field distributions of the prepared nanobeads were observed using COMSOL Multiphysics ^ㄾ (Version 5.4, Sweden) software. First, the thickness of the silica coating layer (window) and the size of the gold nanocolloid were determined and fixed through a scanning electron microscope (SEM), and the average value and standard deviation of the size of the nanobeads were obtained through analysis. The average value and standard deviation of the number of gold nanocolloids attached to the surface of the hydrogel spherical particles before silica coating were analyzed using a transmission electron microscope (JEM-2010, JEOL, Japan).

Based on the above information, after obtaining the extinction spectrum of the nanobeads using software, it was compared with the spectrum obtained using an ultraviolet-visible-infrared spectrometer. Changes in the electric and magnetic fields of the nanobeads according to the wavelength of the incident light were observed using the nanobeads in which the spectra consistent with the experimental results were obtained through trial and error. In determining the structure of the nanobeads, it was assumed that the gold nanocolloidal particles were randomly arranged on the surface of the hydrogel particles. This was determined based on the analysis of scanning electron microscopy results.

For the reliability of the results, the variable change was limited during trial and error. Specifically, the number of gold nanocolloid particles was adjusted within the standard deviation range based on the average number of particles observed through a transmission electron microscope, and based on the average size of nanobeads observed through a scanning electron microscope. The size of the hydrogel particles was adjusted within the standard deviation range.

Results and discussion

Example 1

In the process of preparing the nanobeads (nanobeads prepared using gold nanocolloids having a diameter of 25 nm) prepared according to Example 1, the change in the spectrum of the gold nanocolloids is shown in FIG. 2 .

According to the figure, the gold nanocolloids with a diameter of 25 nm uniformly dispersed in the aqueous phase show the maximum extinction peak at 525 nm, whereas the peak shifts to 535 nm after being mixed with the hydrogel spherical particles. , and the width of the peak also increased slightly. It should be noted that when the temperature of the mixture was raised to 50 °C, the spectrum rapidly changed. Specifically, a shift of the peak to 565 nm was observed and a new peak was generated at 664 nm. At this time, when the temperature is lowered to room temperature, the spectrum becomes almost the same as the spectrum when hydrogel particles and gold nanocolloids are mixed at room temperature.

In order to prepare nanobeads continuously exhibiting left-handed optical properties, coating was performed by sequentially introducing an MPTMS aqueous solution and an NH ₄ OH aqueous solution into a reactor at 50 °C for the structure in which gold nanocolloids were associated on hydrogel particles. After reaction over 5 hours, two peaks in the spectrum shifted to 600 nm and 768 nm. In addition, according to FIG. 3, after forming the silica nano-coating layer, it was observed that the optical properties of the nanobeads did not change even when the external temperature was changed, which indicates that the coating and immobilization were successfully performed. These results suggest that the optical properties of the nanobeads may not be affected by changes in the external environment.

Figure 4a is a scanning electron microscope (SEM) picture of nanobeads prepared using gold nanocolloids with a diameter of 25 nm. The particle size was analyzed to be 190.0 ± 5.8 nm, and the thickness of the silica nano-coating layer was measured to be 10 nm.

As shown in the figure, the nanobead particles were almost spherical, and it could be observed that gold nanocolloids were very densely assembled inside the nanobeads. Based on these observations, changes in the electric and magnetic fields generated when the nanobeads were irradiated with light were observed through the software.

First, a nanobead model having a wavelength closest to the experimental results shown in FIG. 2 was determined as shown in FIG. 4b. When the spectrum as shown in FIG. 4c was obtained, it was calculated that 97 gold nanocolloids were contained on the hydrogel particles in the nanobeads. In this case, the diameter of the nanobeads was calculated to be 190 nm, and the spacing between the gold nanocolloids was calculated to be 1.97 ± 1.07 nm.

As the spectra derived from the model show peaks at 600 nm and 760 nm, when irradiating light with wavelengths of 600 nm and 760 nm corresponding to the peaks, and wavelengths of 680 nm and 800 nm that deviate from the peaks, respectively, The electric and magnetic field distributions of the nanobeads were analyzed, and the results are shown in FIG. 4d.

Referring to the figure, when light having a wavelength of 600 nm was irradiated, electric field resonance and amplification of light components appeared around the gold nanocolloid, while no noticeable magnetic field amplification was observed. In addition, when light having a wavelength of 680 nm was irradiated, similar results to those obtained when irradiating a wavelength of 600 nm were obtained.

On the other hand, when light having a wavelength of 760 nm was irradiated, electric field resonance and amplification phenomena appeared around the gold nanocolloids, and strong magnetic field resonance and amplification phenomena were observed inside the nanobeads. This is because a strong magnetic field is formed inside the nanobeads, and as a result, the LC It suggests that there is a high probability that it has a circuit. According to FIG. 4D, this magnetic field amplification phenomenon was significantly stronger than the strength of the externally applied magnetic field. When light having a wavelength of 800 nm was irradiated, magnetic field resonance and amplification phenomena were observed inside the nanobeads as in the case of irradiating light having a wavelength of 760 nm. However, it was observed that the intensity of magnetic field resonance amplification was weak compared to the case where light having a wavelength of 760 nm was irradiated.

Due to this resonance phenomenon, the vector (magnitude and direction) of the electric dipole moment and magnetic dipole monoment formed in the nanobead is changed to various phase angles of the incident plane wave; The results observed for the phase, φ) are shown in FIG. 5 .

Referring to the figure, in the case of a 600 nm peak, it can be confirmed that the electric field generated in the nanobeads does not have a constant direction with respect to the applied electromagnetic field and is amplified. In addition, it can be confirmed that the magnetic field generated in the nanobeads in relation to the applied electromagnetic field is generated around the gold nanocolloids present on the surface of the nanobeads. On the other hand, when light having a wavelength of 760 nm was irradiated, it was observed that the electric field was circularly oriented in a constant direction around the surface of the nanobeads. In addition, an amplification phenomenon due to strong magnetic field resonance was observed inside the nanobeads, as shown in FIG. 4d. That is, it is presumed that the generation of the magnetic field due to the strong magnetic field resonance and amplification inside the nanobeads originates from the electric field generated in the form of a coil with a constant direction outside the nanobeads. The direction of the electric field generated from the nanobeads is generated clockwise when the phase angle is 0°, and generated counterclockwise when the phase angle is 180°, and the strength of the amplified magnetic field has the same value. Observed.

Although the present invention is not bound by any particular theory, the reason why the above results are obtained can be explained as follows.

Referring to FIG. 5, when the phase angle is 0°, the direction of the electric field generated inside the nanobeads is clockwise, which is similar to a state in which a capacitor is maximally charged in an L-C circuit. can When the phase angle changed from 0° to 90°, the formed electric field disappeared and an induced magnetic field was formed. This is similar to a situation in which a magnetic field is formed inside an inductor by converting it into an induced current or a circular electric current when the capacitor charged in the L-C circuit is discharged. In addition, when the phase angle is changed from 90° to 180°, the formed induced magnetic field disappears, and the electric field is formed in a counterclockwise direction unlike when the phase angle is 0°. This can be said to be similar to the situation where the energy of the inductor recharges the capacitor in the L-C circuit.

The above results can be inferred that an artificial magnetic material that reacts to a magnetic field is formed due to the arrangement of gold nano-colloids, which are non-magnetic materials. Therefore, when the effective permeability of nanobeads composed of gold nanocolloids capable of having a negative permittivity at a specific wavelength is controlled to have a negative value, it suggests that a negative refractive index may be expressed.

In order to check whether the nanobeads prepared in this example can refract light of a specific wavelength in the direction opposite to the direction of incident propagation, a change in the Poynting vector was observed. In this regard, the Poynting vector represents the propagation direction of the electromagnetic wave together with the energy density of the electromagnetic wave. Therefore, the presence or absence of left-handed optical characteristics can be confirmed from the information on the direction of the Poynting vector formed in nanobeads with respect to the direction of the Poynting vector of light having a specific wavelength. The results are shown in FIG. 6 . The figure indicates the change (blue arrow) of the Poynting vector occurring inside the nanobeads when light having a wavelength of 600 nm and 760 nm is incident from a direction inclined at 30° with respect to the longitudinal axis (orange arrow). Specifically, as shown in FIG. 6, when light having a wavelength of 600 nm is incident, the direction of the Poynting vector generated from nanobeads is directed toward the incident direction of light, whereas when light having a wavelength of 760 nm is incident showed that the direction of the Poynting vector generated from the nanobeads was directed toward the point of incidence, which is opposite to the incident direction of light. However, the analysis results of these Poynting vectors may change depending on the conditions during calculation (e.g. medium, boundary conditions, volume fraction of nanobeads, arrangement spacing between nanobeads, etc.), but the refractive index of nanobeads is indicates that it can have a negative value.

Example 2

7 shows the spectral change of the gold nanocolloid during the process of preparing the nanobeads prepared according to Example 2 (nanobeads prepared using gold nanocolloids having a diameter of 40 nm).

According to the figure, while the gold nanocolloids with a diameter of 40 nm uniformly dispersed in the aqueous solution exhibited the maximum extinction peak at 527 nm, after mixing with the hydrogel spherical particles, it moved to 531 nm, and the peak width also increased slightly.

At this time, it should be noted that when the temperature of the mixture was raised to 50 ° C., the spectrum rapidly changed, specifically, the peak shifted to 564 nm and a new peak was generated at 729 nm. In order to prepare nanobeads exhibiting continuous left-handed optical properties, coating was performed by sequentially introducing an MPTMS aqueous solution and an NH ₄ OH aqueous solution into a reactor at 50 °C for the structure in which gold nanocolloids were associated on hydrogel particles. After reaction over 5 hours, the peaks shifted to 610 nm and 870 nm. After the formation of the silica nano-coating layer, as shown in FIG. 8, it was observed that the optical properties of the nanobeads did not change even when the external temperature changed, and it was determined that the coating and immobilization were successfully performed. This suggests that the optical properties of the nanobeads may not be affected.

9a is a scanning electron micrograph of nanobeads prepared using gold nanocolloids having a diameter of 40 nm.

According to the figure, the average size of the particles was analyzed to be 210.0 ± 10.7 nm, and the thickness of the silica nano-coated window was measured to be 11 nm. In addition, the nanobead particles were almost spherical, and it could be observed that gold nanocolloids were very densely assembled inside the nanobeads. Based on these observations, changes in electric and magnetic fields generated when nanobeads were irradiated with light were observed using software.

First, a nanobead model having a wavelength closest to the experimental results shown in FIG. 7 was determined as shown in FIG. 9B. When the spectrum as in FIG. 9c was obtained, it was calculated that 40 gold nanocolloids were contained on the hydrogel particles within the nanobeads. In this case, the diameter of the nanobeads was calculated to be 210 nm, and the spacing between the gold nanocolloids was calculated to be 1.76 ± 1.45 nm.

Referring to the figure, the peaks of the nanobeads were observed at 610 nm and 870 nm, and the extinction spectrum range was also observed to be very wide. As a result of modeling, it was shown that various peaks were generated between 570 nm and 870 nm. Among them, electric and magnetic field distributions were investigated when light was irradiated for three characteristic peaks, that is, 570 nm, 760 nm, and 870 nm, and the results are shown in FIG. 9D.

According to the figure, when light of 570 nm and 760 nm was irradiated, electric field resonance and amplification of light components appeared around the gold nanocolloid, but no noticeable magnetic field resonance was observed. On the other hand, when 870 nm light was irradiated, electric field resonance and amplification phenomena appeared around the gold nanocolloids, and magnetic field resonance and amplification phenomena were observed inside the nanobeads. This means that a strong magnetic field is formed inside the nanobeads, suggesting that they are likely to have an L-C circuit. Also, according to FIG. 9D , this magnetic field amplification phenomenon was significantly stronger than the strength of the externally applied magnetic field.

The vector (magnitude and direction) of the electric dipole moment and magnetic dipole monoment formed in the gold nanocolloid due to the formation of such a magnetic field was observed for various phase angles ( φ ) of the incident plane wave. The results are shown in Figure 9e.

Referring to the figure, when the nanobeads are irradiated with light having a wavelength of 870 nm, it can be observed that the electric field is circularly oriented in a constant direction around the surface of the nanobeads. In addition, an amplification phenomenon due to strong magnetic field resonance was observed inside the nanobeads, as shown in FIG. 9d. That is, it is presumed that the generation of the magnetic field due to the strong magnetic field resonance and amplification inside the nanobeads originates from the electric field generated in the form of a coil with a constant direction outside the nanobeads. The direction of the electric field generated from the nanobeads is clockwise when the phase angle is 0°, and counterclockwise when observed at 180°, which is a mirror image, so the strength of the amplified magnetic field is also the same value was observed to have

Although the present invention is not bound by any particular theory, the reason why the above results are obtained can be explained as follows.

Referring to FIG. 9E , when the phase angle is 0°, the direction of the electric field generated inside the nanobeads is clockwise. When the phase angle changed from 0° to 90°, the formed electric field disappeared and an induced magnetic field was formed. In addition, when the phase angle changes from 90° to 180°, the induced magnetic field that was formed disappears, and the electric field is formed in a counterclockwise direction unlike the case where the phase angle is 0°.

These results suggest that, as in the case of nanobeads using 25 nm gold nanoparticles, an artificial magnetic material that reacts to a magnetic field is formed due to the arrangement of gold nanoparticles, which are non-magnetic materials. When the effective permeability of nanobeads composed of gold nanocolloids having a dielectric constant of is controlled to have a negative value, it is implied that a negative refractive index can be expressed.

In order to check whether the nanobeads prepared in this example can refract light of a specific wavelength in the direction opposite to the incident propagation direction, the change in the Poynting vector was observed, and the results are shown in FIG. 9F. The above figure shows the change (blue arrow) of the Poynting vector occurring inside the nanobead when light having a wavelength of 870 nm is incident from a direction inclined at 30° with respect to the longitudinal axis of the nanobead (orange arrow). . As shown in FIG. 9f, when light having a wavelength of 870 nm is incident, the direction of the Poynting vector generated from the nanobeads is mostly directed toward the incident point opposite to the incident direction of the light. This result can be said to appear because the refractive index of the nanobeads has a negative value. However, the analysis results of these Poynting vectors may change depending on the conditions during calculation (e.g. medium, boundary conditions, volume fraction of nanobeads, arrangement spacing between nanobeads, etc.), but the refractive index of nanobeads is indicates that it can have a negative value.

All simple modifications or changes of the present invention belong to the scope of the present invention, and the specific scope of protection of the present invention will be clarified by the appended claims.

Claims (15)

spherical hydrogel particles;
a plurality of non-magnetic metal nano-colloidal particles associated with the hydrogel particle surface; and
a light-transmitting inorganic oxide nano-coating layer formed on the hydrogel particles to which the metal nano-colloidal particles are attached;
A three-dimensional structure of nanobeads having left-handed optical properties comprising
The metal nanocolloidal particles are associated with the surface of the hydrogel particles so that the nanobeads exhibit left-handed optical characteristics by simultaneously generating and amplifying electric and magnetic field resonances therein in a predetermined optical frequency band to form an inductance-capacitance circuit form a structure,
The inorganic oxide nano-coating layer provides a fixing force to the association structure of metal nano-colloids formed on the hydrogel particles to preserve left-handed optical properties, and
Nanobeads having a diameter of the nanobeads are determined in the range of 100 to 1500 nm. According to claim 1, Nanobeads characterized in that the diameter (hydrodynamic diameter) of the hydrogel particles is controlled within the range of 50 to 1000 nm. The method of claim 1, wherein the hydrogel is poly(N-isopropylacrylamide) [poly(N-isopropylacrylamide), pNIPAM], poly(N-isopropyl acrylamide-co-allylamine) [poly(N-isopropyl acrylamide-co-allylamine), poly(NIPAM-co-AA)], poly(N-isopropylacrylamide-co-2-(dimethylamino)ethyl methacrylate) [poly(Nisopropylacrylamide-co-2-(dimethylamino )ethyl methacrylate), poly(NIPAM-co-DMAEMA)], poly(N-isopropyl acrylamide-co-2-(dimethylamino)ethyl acrylate)[poly(N-isopropyl acrylamide-co-2-(dimethylamino )ethyl acrylate), poly(NIPAM-co-DMAEA)], poly(N-isopropyl acrylamide-co-acrylic acid)[poly(N-isopropyl acrylamide-co-acrylic acid), poly(NIPAM-co-AAc) ], poly(N-isopropyl acrylamide-co-methacrylic acid) [poly(N-isopropyl acrylamide-co-methacrylic acid), poly(NIPAM-co-MAAc)], poly(N,N-diethylacrylamide )[poly(N,N-diethylacrylamide)], poly(N-vinylcaprolactam)[poly(N-vinlycaprolactam)], poly(ethylene glycol)[poly(ethylene glycol)], poly(ethylene glycol-b- Nanobeads, characterized in that at least one selected from the group consisting of propylene glycol-b-ethylene glycol) [poly (ethylene glycol-b-propylene glycol-b-ethylene glycol)]. The nanobeads of claim 1, wherein the diameter of the metal nano-colloidal particles is controlled within a range of 1 to 200 nm. The nanobead according to claim 1, wherein the distance between the metal nanocolloid particles in the association structure is determined within the range of 0.1 to 20 nm. The nanobeads of claim 1, wherein the material of the metal nanocolloidal particles is at least one selected from the group consisting of gold, silver, platinum, palladium, copper and aluminum. The method of claim 1, wherein the metal nanocolloid particle: hydrogel particle diameter ratio is controlled in the range of 1: 2 to 1000, and
The thickness of the inorganic oxide nanocoating layer: the ratio of the hydrogel diameter is 1: nanobeads, characterized in that controlled in the range of 0.5 to 500. The nanobeads of claim 1, wherein the thickness of the inorganic oxide nanocoating layer is determined within a range of 1 to 1000 nm. The nanobeads of claim 1, wherein the inorganic oxide nano-coating layer is at least one selected from the group consisting of silica, alumina, titania, and zinc oxide. The nanobead according to claim 1, wherein the predetermined optical frequency band is selected from the visible light-near infrared band. a) providing an aqueous dispersion of metal nanocolloidal particles;
b) apart from step a), providing an aqueous dispersion of spherical hydrogel particles;
c) combining the aqueous dispersion of the metal nanocolloid particles and the aqueous dispersion of the hydrogel particles under controlled temperature conditions to associate the metal nanocolloid on the hydrogel particles; and
d) forming a light-transmitting inorganic oxide nano-coating layer on the hydrogel particles in which the metal nano-colloids are associated using an inorganic oxide precursor;
A method for producing a three-dimensional structure of nanobeads having left-handed optical properties comprising
Forming a structure in which the metal nanocolloidal particles are associated with the surface of the hydrogel particles so that the nanobeads exhibit left-handed optical characteristics in a predetermined optical frequency band to simultaneously generate and amplify electric and magnetic field resonances therein,
The inorganic oxide nano-coating layer provides a fixing force to the association structure of metal nano-colloids formed on the hydrogel particles to preserve left-handed optical characteristics. The method of claim 11, wherein in step c), the hydrogel particles and the metal nanocolloid particles are associated with each other by being attached to the surface of the hydrogel particle by electrostatic attraction, and
The method characterized in that the association structure between the metal nano-colloidal particles associated with the surface thereof and the distance and density between the metal nano-colloidal particles are changed accordingly by the reversible expansion and contraction of the hydrogel particles. The method of claim 11, wherein the concentration of each of the aqueous dispersion of metal nanocolloidal particles of step a) and the aqueous dispersion of spherical hydrogel particles of step b) ranges from 0.001 to 0.3% by weight and from 0.01 to 10% by weight. A method characterized in that determined in. The method of claim 12, wherein the zeta potential (30 ℃) of the hydrogel particles is in the range of 5 to 40 mV, the zeta potential (30 ℃) of the metal nano-colloidal particles is -70 to -10 mV range, characterized in that method. The method of claim 11, wherein the material of the inorganic oxide nano-coating layer is silica, and the precursor thereof is a silane-based compound, MPTMS (mercaptopropyl trimethoxysilane), TEOS (tetraethyl orthosilicate), TMOS (trimethoxy orthosilicate), GPTMS ((3-glycidoxypropyl)methyldiethoxysilane ), a method characterized in that at least one selected from the group consisting of GOTMS (γ-glycidyloxypropyl trimethoxysilane), APTMOS (aminophenyl trimethoxysilane), and APTES (aminopropyl triethoxysilane).

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