HK1188300A - Temperature sensitive composite for photonic crystals - Google Patents

Description

Temperature sensitive composite for photonic crystals

Background

Technical Field

The present invention relates to thermally responsive crystals, particularly inverse opal photonic crystals, which contain a material within the inverse opal voids that responds to temperature changes, thereby altering the band gap of radiation reflected by the photonic crystal.

Description of the Related Art

A photonic crystal is an optical material with a refractive index that varies in multiple dimensions. Photonic crystals can be produced from crystalline colloidal arrays that reflect radiation over a range of wavelengths according to bragg's law, depending on the composition of the materials in the array, the particle size, the packing arrangement within the array, and the degree of regularity of the array. Crystalline colloidal arrays have been used as three-dimensional ordered arrays of monodisperse colloidal particles, which are typically composed of a polymer latex (e.g., polystyrene) or an inorganic material (e.g., silica). Colloidal dispersions of particles can form crystalline structures with lattice spacings comparable to the wavelength of radiation in the ultraviolet, visible, or infrared wavelength ranges. Such crystalline structures have been used to filter a narrow band of selected wavelengths from a broad spectrum of incident radiation while allowing transmission of adjacent wavelengths of radiation.

Such crystalline colloidal arrays typically have constant interparticle spacing within the array, while other crystalline colloidal arrays may be thermally active as their interparticle voids change in response to stimuli, such as temperature changes. Thermally responsive crystalline colloidal arrays are traditionally produced from hydrogels. In hydrogel-based devices, monodisperse, highly charged colloidal particles are dispersed in an aqueous medium. Due to the electrostatic charge, the particles self-assemble into a crystalline colloidal array. The ordered structure diffracts radiation according to bragg's law, wherein radiation satisfying the bragg condition is reflected, while adjacent spectral regions not satisfying the bragg condition are transmitted through the device. An array of particles that diffract radiation according to bragg's law satisfies the equation: m λ =2ndsin θ

Where m is an integer, λ is the wavelength of the reflected radiation, n is the effective refractive index of the array, d is the spacing between the particle layers, and θ is the angle formed by the reflected radiation and the plane of the particle layers. Thus, by increasing the particle size or volume of the matrix between the particles of each layer, the inter-ionic distance (d) between the particle layers is increased, thereby changing the wavelength of the diffracted radiation. The particle size and/or matrix volume may be increased by responding to an excitation, such as a temperature change, that causes the particle or matrix to expand. Likewise, a change in the effective refractive index of the array can change the wavelength of the diffracted radiation.

Other photonic crystals are based on inverse opals. Synthetic opal structures have been produced by uniformly sized submicron silica spheres arranged in an ordered periodic array. The voids between the silica spheres are filled with a matrix material and then the silica spheres are dissolved, thereby creating a periodic array of voids within the uniform matrix material. The voids may be filled with a filler composition to adjust the optical properties of the inverse opal.

Summary of The Invention

The present invention includes a composite photonic crystal comprising an inverse opal structure defining an ordered array of voids, and a filler composition received by the voids, wherein a property of the filler composition changes in response to an excitation, thereby changing a bandgap of radiation reflected by the composite photonic crystal. The invention also includes a method of detecting a change in temperature, comprising: providing a composite photonic crystal comprising an inverse opal structure defining an ordered array of voids and a filler composition received by the voids, wherein a property of the filler composition changes in response to a change in temperature; changing the temperature of the composite photonic crystal; and detecting a change in the photonic band gap of the composite photonic crystal. A method of fabricating a temperature responsive composite photonic crystal comprising: preparing an inverse opal defining a plurality of voids, filling the voids with a polymerizable filler composition, and polymerizing the filler composition, wherein properties of the filler composition change in response to a change in temperature, thereby changing a bandgap of radiation reflected by the composite photonic crystal.

Brief Description of Drawings

FIG. 1 is a graph of the response of diffraction peaks of the material of the present invention to changes in temperature.

Description of the preferred embodiments

In the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

In this application, unless specifically indicated otherwise, the use of the singular includes the plural and the plural includes the singular. Further, in this application, the use of "or" means "and/or" unless specifically stated otherwise, however "and/or" may be explicitly used in certain situations.

The term "polymer" shall include homopolymers, copolymers and oligomers. The term "metal" includes metals, metal oxides and metalloids. The term "injection" and related terms such as injection (infusion) refer to permeation from a liquid phase.

Composite photonic crystal

The present invention includes a temperature sensitive composite photonic crystal for controlling the wavelength of radiation reaching a substrate. The material of the invention diffracts radiation in the electromagnetic spectrum of visible and/or non-visible light and further comprises a method for its manufacture. The present invention is described with reference to diffraction wavelengths or diffraction peaks, which refer to the peak bands of radiation reflected by diffraction from the materials of the present invention. Thus, "diffracted wavelength" refers to a band of radiation having a wavelength that generally satisfies bragg's law. The reflected radiation may be in the visible spectrum or in the invisible spectrum (e.g., infrared or ultraviolet radiation).

The composite photonic crystal of the present invention comprises an inverse opal structure defining an ordered array of voids, and a filler composition received by the voids. The properties of the filler composition change in response to an excitation, such as a change in temperature, thereby changing the bandgap of the radiation reflected by the composite photonic crystal. In one embodiment, the refractive index of the filler composition changes in response to an excitation, such as a temperature change. Thus, the effective refractive index of the composite photonic crystal changes. The change in effective refractive index shifts the wavelength (λ) of diffraction. The shift in diffraction wavelength caused by the composite photonic crystal also affects the contrast associated with the composite photonic crystal, as determined by the amount of radiation reflected thereby. Thus, by applying an excitation, such as a temperature change, the photonic crystal will exhibit a change in diffraction wavelength, as well as a change in contrast.

The inverse opals used to produce the composite photonic crystals of the present invention may be produced according to conventional techniques. For example, a periodic array of particles can be produced and backfilled with a matrix composition, which is then fixed in place around the ordered array of particles. By "fixed" herein is meant that the matrix material is solidified or cross-linked or otherwise fixed around the particles, resulting in a crystalline ordered array. The particles may be removed from the array by dissolving the particles in a solvent or by heating the material to degrade and volatilize the particles. For example, polystyrene particles or other polymer particles may be dissolved in a solvent, such as toluene, followed by evaporation of the toluene by heating, thereby producing an inverse opal structure. The resulting inverse opal comprises a fixed matrix material having a periodic array of voids therein. The present invention is not limited to the technique used to produce such inverse opals nor to the material removed to produce the particles of inverse opals.

Suitable materials for use as the filler composition received into the interstices of the inverse opal include materials having properties that change with excitation. One non-limiting example of an excitation is a temperature change, wherein the temperature change causes a change in a property of the filler material. In one embodiment, the electrical conductivity of the filler composition changes with temperature. For example, a filler composition that exhibits a change in conductivity in response to a change in temperature can switch between functioning as a conductor and functioning as an insulator (or vice versa) upon a change in temperature, such as vanadium dioxide or the like. The change in the electrical conductivity of the filler composition within the voids of the inverse opal changes the refractive index of the filler composition, thereby changing the difference in refractive index between the filled voids and the matrix surrounding the inverse opal. A change in the difference in refractive index between the filled voids and the matrix changes the contrast of the composite photonic crystal, which can be detected as a change in the amount of radiation reflected by the composite photonic crystal. For radiation reflected in the visible spectrum, contrast changes may be detected as an increase or decrease in the brightness of the reflected radiation. In addition, the change in the refractive index of the filler composition also changes the effective refractive index of the composite photonic crystal, thereby shifting the diffraction wavelength. Thus, when the conductor-insulator material is used as a filler composition for a composite photonic crystal, temperature changes result in contrast changes and diffraction wavelength shifts.

In another embodiment, the filler composition includes a polymer composition having a configuration that changes with changes in temperature. "configuration" herein refers to the three-dimensional shape of the constituent polymeric chains. One suitable polymeric material is a side chain crystalline polymer, such as an acrylic material having at least 8 carbon atoms, e.g., stearyl acrylate. Generally, as the side chains of the polymer relax at higher temperatures, the volume of space occupied by the side chain crystalline polymer increases with increasing temperature, thereby expanding the polymer configuration to occupy a larger volume of space.

In one embodiment of the invention, the side chain crystalline polymer is generated in situ in the interstices of the inverse opal. The monomer precursor is filled into the voids and polymerized within the voids, such as by Ultraviolet (UV) curing, to produce a polymeric material that remains within the voids. Monomers that can be used to produce the side chain crystalline polymer include tetradecyl (meth) acrylate, hexadecyl (meth) acrylate, octadecyl (meth) acrylate, eicosyl (meth) acrylate, docosyl (meth) acrylate.

The composite photonic crystal of the present invention is particularly suitable for filtering the bandgap of radiation. For example, the photonic crystals of the present invention can be used to control infrared radiation reaching a substrate. Infrared radiation in the sun can heat surfaces of buildings, roads, and the like. The photonic crystal of the present invention may be tuned such that when the photonic crystal reaches a predetermined temperature deemed unacceptable for the underlying surface, the filler composition held within the voids changes in a manner that causes a shift in the diffraction wavelength, thereby reflecting a particular band gap, such as infrared radiation. Composite photonic crystals produced according to the present invention that reflect infrared radiation when the temperature reaches a predetermined level can be used to control the heating of a surface by sunlight. For example, a composite photonic crystal that reflects infrared radiation at elevated temperatures may be applied to surfaces of buildings or vehicles or other structures that are exposed to sunlight. When the surface of the structure reaches a predetermined temperature, the diffraction wavelength of the composite photonic crystal thereon shifts, causing infrared radiation to be reflected. Upon cooling, the diffracted wavelength shifts back so that infrared radiation is no longer reflected. Alternatively, the band gap can be adjusted so that infrared radiation reaching the surface passes through the photonic crystal and is not reflected, thereby heating the underlying structure. By having infrared radiation reach the underlying structure, the structure can be heated, thereby preventing ice build-up on the surface in winter. It is to be understood that the filler composition received within the voids of the composite photonic crystal of the present invention can be tailored such that the bandgap of radiation reflected from the composite photonic crystal has a desired effect on the substrate with which the composite photonic crystal is carried, e.g., reflection of infrared radiation or allowing infrared radiation to pass therethrough, and reflection of another bandgap (e.g., visible radiation).

As detailed below, the composite photonic crystal may be prepared on a substrate that functions as a temporary carrier or on a substrate that is the desired end use for the composite photonic crystal. By temporary support is meant that the substrate is used to support the production of the composite photonic crystal of the present invention, which is subsequently removed from the substrate in a self-supporting form, such as a thin film or crushed particulates in a self-supporting form. The thin film of composite photonic crystals or particulates of composite photonic crystals can then be applied to another substrate or added to a composition (e.g., a coating composition) for its final end use. The end use and final form of the temperature responsive material is not limited to those described herein.

Base material

The substrate may be a flexible material such as a metal sheet or foil (e.g. aluminium foil), paper, or a film (or sheet) of polyester or polyethylene terephthalate (PET), or a non-flexible material such as glass or plastic. By "flexible" is meant that the substrate is capable of undergoing mechanical stress, such as bending, stretching, compressing, and the like, without significant irreversible change. One suitable substrate is a microporous sheet. Some examples of microporous sheets are described in us patent 4,833,172; 4,861,644, and 6,114,023, which are incorporated herein by reference. Commercially available microporous sheets are known by the name PPG Industries, incAnd (5) selling. Other suitable flexible substrates include natural leather, synthetic leather, finished natural leather, finished synthetic leather, suede, vinyl nylon, ethylene vinyl acetate foam (EVA foam), Thermoplastic Polyurethane (TPU), fluid-filled bladders, polyolefin and polyolefin blends, polyvinyl acetate and copolymers thereof, polyvinyl chloride and copolymers thereof, polyurethane elastomers, synthetic textiles, and natural textiles.

In certain embodiments, the flexible substrate is a compressible substrate. "compressible substrate" and like terms refer to a substrate that can undergo a compressive deformation and can recover to substantially the same shape once the compressive deformation stops. The term "compressive deformation" denotes a mechanical stress that at least temporarily reduces the volume of the substrate in at least one direction. The compressible substrate is one, for example, having a compressive strain of 50% or greater, such as 70%, 75%, or 80% or greater. Specific examples of compressible substrates include those comprising polymeric bladders and foams filled with air, liquid, and/or plasma. A "foam" may be a polymeric or natural material that includes an open cell foam and/or a closed cell foam. "open cell foam" refers to a foam comprising a plurality of interconnected air cells; "closed cell foam" refers to a foam comprising discontinuous closed cells. Examples of foams include, but are not limited to, polystyrene foams, polyvinyl acetate and/or copolymers thereof, polyvinyl chloride and/or copolymers thereof, poly (meth) acrylimide foams, polyvinyl chloride foams, polyurethane foams, thermoplastic polyurethane foams, polyolefin foams, and polyolefin blends. Polyolefin foams include, but are not limited to, polypropylene foams, polyethylene foams, and Ethylene Vinyl Acetate (EVA) foams. "EVA foam" can include open cell foams and/or closed cell foams. The EVA foam may comprise a flat sheet or plank or a molded EVA foam, such as a midsole for a shoe. Different types of EVA foam may have different types of surface porosity. Molded EVA foam includes a dense surface or skin, while a flat sheet or slab has a porous surface.

The polyurethane substrates according to the invention include aromatic, aliphatic and hybrid (hybrid examples are silicone polyether or polyester polyurethane, and silicone carbonate polyurethane) polyester or polyether based thermoplastic polyurethanes. "Plastic" refers to any of the common thermoplastic or thermoset synthetic materials, including thermoplastic olefins (TPOs) such as polyethylene and polypropylene and blends thereof, thermoplastic polyurethanes, polycarbonates, sheet molding compounds, reaction injection molding compounds, acrylonitrile-based materials, nylons, and the like. One particular plastic is a TPO comprising polypropylene and EPDM (ethylene propylene diene monomer).

The composite photonic crystal may be applied to the article in various ways. In one embodiment, such materials are prepared on a substrate and then removed from the substrate as a free-standing film or are comminuted into particulate form, for example in the form of flakes. The comminuted composite photonic crystals may be incorporated as an additive into a coating for application to an article. Haze can be advantageously minimized within coating compositions comprising the comminuted composite photonic crystals. Reduced haze can be obtained by reducing the difference in refractive index between the matrix and the particles of the composite. However, a reduction in the difference in refractive index generally reduces the intensity of the reflected radiation. Therefore, when it is desired that the minimum difference in haze and refractive index is reduced, the strength can be maintained by increasing the thickness of the composite photonic crystal, that is, by increasing the number of particle layers in the material, as compared to a material in which the refractive indices of the matrix and the particles are more different from each other.

In one embodiment, the coating composition comprises a "hard coat", such as an alkoxide. The alcoholate can be further mixed and/or reacted with other compounds and/or polymers known in the art. Particularly suitable are compositions comprising siloxanes formed by at least partially hydrolyzing organoalkoxysilanes (e.g., one within the above general formula). Suitable alcoholate-containing compounds and methods for their preparation are described in U.S. patent 6,355,189; 6,264,859, respectively; 6,469,119, respectively; 6,180,248, respectively; 5,916,686, respectively; 5,401,579, respectively; 4,799,963, respectively; 5,344,712, respectively; 4,731,264, respectively; 4,753,827, respectively; 4,754,012, respectively; 4,814,017, respectively; 5,115,023, respectively; 5,035,745, respectively; 5,231,156, respectively; 5,199,979, respectively; and 6,106,605, which are hereby incorporated by reference.

In certain embodiments, the alcoholate comprises glycidoxy [ (C)₁-C₃) Alkyl radical]III (C)₁-C₄) Alkoxysilane monomer and tetrakis (C)₁-C₆) A combination of alkoxysilane monomers. Glycidoxy [ (C) groups suitable for use in the coating compositions of the present invention₁-C₃) Alkyl radical]III (C)₁-C₄) The alkoxy silane monomer comprises glycidoxymethyl triethoxy silane, alpha-glycidoxyethyl trimethoxy silane, alpha-glycidoxyethyl triethoxy silaneOxysilanes, beta-glycidoxyethyltrimethoxysilanes, beta-glycidoxyethyltriethoxysilanes, alpha-glycidoxypropyltrimethoxysilane, alpha-glycidoxypropyltriethoxysilane, beta-glycidoxypropyltrimethoxysilane, beta-glycidoxypropyltriethoxysilane, gamma-glycidoxypropyltrimethoxysilane, hydrolysates thereof, and/or mixtures of these silane monomers. Can be used in combination with the glycidoxy [ (C) groups in the coating composition of the present invention₁-C₃) Alkyl radical]III (C)₁-C₄) Tetrakis (C) in combination with alkoxysilane monomer₁-C₆) The alkoxysilane monomer includes, for example, materials such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tetrapropoxysilane, tetrahexoxysilane, and mixtures thereof.

In certain embodiments, the glycidoxy [ (C) groups used in the coating compositions of the present invention₁-C₃) Alkyl radical]III (C)₁-C₄) Alkoxysilane and tetrakis (C)₁-C₆) The alkoxysilane monomer glycidoxy [ (C) in a weight ratio₁-C₃) Alkyl radical]III (C)₁-C₄) Alkoxysilane: fourthly (C)₁-C₆) The alkoxysilane is present from 0.5:1 to 100:1, such as from 0.75:1 to 50:1, and in some cases from 1:1 to 5: 1. In certain embodiments, the alkoxide is at least partially hydrolyzed prior to combining with other components of the coating composition, such as polymer encapsulated dyed particles. Such hydrolysis reactions are described in U.S. patent No. 6,355,189, column 3, lines 7 to 28, the cited portions of which are incorporated herein by reference. In certain embodiments, the water is provided in an amount necessary for hydrolysis of the hydrolyzable alcoholate. For example, in certain embodiments, water is present in an amount of at least 1.5 moles of water per mole of hydrolyzable alkoxide. In certain embodiments, atmospheric moisture, if sufficient, may also be sufficient.

In certain embodiments, a catalyst is provided for catalyzing the hydrolysis and condensation reactions. In certain embodiments, the catalyst is an acidic material and/or a material different from the acidic material that generates an acid when exposed to actinic radiation. In certain embodiments, the acidic material is selected from an organic acid, a non-biological acid, or a mixture thereof. Non-limiting examples of such materials include acetic acid, formic acid, glutaric acid, maleic acid, nitric acid, hydrochloric acid, phosphoric acid, hydrofluoric acid, sulfuric acid, or mixtures thereof.

Any material that generates an acid when exposed to actinic radiation may be used as a hydrolysis and condensation catalyst in the coating composition of the present invention, such as lewis acids and/or bronsted acids. Non-limiting examples of acid generating compounds include onium salts and iodosyl salts, aromatic diazonium salts, metallocene salts, o-nitrobenzaldehyde, polyoxymethylene polymers described in U.S. Pat. No. 3,991,033, ortho-nitro esters described in U.S. Pat. No. 3,849,137, o-nitrophenyl acetals, their polyesters, and end-capped derivatives described in U.S. Pat. No. 4,086,210, sulfonic acid esters, or aromatic alcohols containing a carbonyl group in the alpha or beta position of the sulfonate ester group, N-sulfonyloxy derivatives of aromatic amides or imides, aromatic oxime sulfonates, quinone diazides, and resins having benzoin groups along the chain, such as those described in U.S. Pat. No. 4,368,253. Examples of these radiation activated acid catalysts are also disclosed in U.S. Pat. No. 5,451,345.

In certain embodiments, the acid generating compound is a cationic photoinitiator, such as an onium salt. Non-limiting examples of such materials include diaryliodonium salts and triarylsulfonium salts as available from Sartomer CompanyCD-1012 and CD-1011 are commercially available. Other suitable onium salts are described in U.S. Pat. No. 5,639,802, column 8, line 59 to column 10, line 46. Examples of such onium salts include 4, 4' -dimethyldiphenyliodonium tetrafluoroborate, phenyl-4-octyloxyphenyliodonium hexafluoroantimonate, dodecyldiphenyliodonium hexafluoroantimonate, [4- [ (2-tetradecanol) oxy group]Phenyl radical]Phenyl iodonium hexafluoroantimonateSalts, and mixtures thereof.

The amount of catalyst used in the coating composition of the present invention can vary widely and depends on the particular material used. Only amounts which catalyze and/or initiate the hydrolysis and condensation reactions, e.g., catalytic amounts, are required. In certain embodiments, the acidic material and/or the acid generating material may be used in an amount of 0.01 to 5 weight percent based on the total weight of the composition.

The composite photonic crystals of the present invention may also be used in marking devices, including valuable documents, articles and their packaging, as well as certification material, particularly an anti-counterfeiting device. Examples of documents of value include currency, credit cards, compliance certificates, collectibles and transaction cards, contracts, ownership or license plate numbers (e.g., cars), regulatory compliance decals, tickets (e.g., travel, event or parking), tax stamps, coins, stamps, checks and money orders, stationery, lottery tickets, currency and/or tokens, control items (e.g., evidence), key cards, keys, tracking and tracking items, and as part of bar codes. Articles or packaging for articles can include aircraft parts, automotive parts, such as vehicle identification numbers, medical and personal care products, recording media, clothing and shoes, electronic devices, batteries, ophthalmic devices, wine, food, printing inks and consumables, writing implements, luxury items, such as luggage and handbags, sporting goods, software and software packaging, tamper seals, artwork (including artwork originals), building materials, munitions, toys, fuel, industrial equipment, biological materials, and living goods, jewelry, books, antiques, security devices (e.g., fire extinguishers and filtration devices), carpets and other devices, chemicals, medical devices, paints and coatings, and windows and slides. Examples of certificates having the composite photonic crystal of the present invention include driver's licenses, identification cards (government, community, and educational), passports, visas, marriage certificates, hospital bracelets, and academic certificates. These examples should not be limiting, but are merely a sampling of devices that may have the composite photonic crystal of the present invention. Such use is not meant to be limiting.

Alternatively, the composite photonic crystal may be fabricated in the form of a film and then applied to an article, such as by an adhesive or the like.

Alternatively, the product itself may be used directly as a substrate by applying the composite photonic crystal directly to the housing of a product, such as the housing of an electronic device, or directly to goods, such as sports equipment, ornaments, optical lenses, optical frames, clothing (including shoes, etc.).

The composite photonic crystals of the present invention may be used to authenticate articles, such as documents or devices, or to authenticate the origin of the products produced. A document, such as a security card, having a composite photonic crystal of the present invention would be considered authentic if the document with a temperature responsive material could exhibit its properties, such as responsiveness to temperature changes. A "security card" includes a document or device that authenticates the identity of its holder or allows access to a facility, for example in the form of a badge. The security card may authenticate the holder of the card (e.g., a photo-id card or passport) or may serve as a document or device indicating that the holder may be allowed access to a secure facility. For example, security cards that exhibit authenticity may be tested for the property of diffracting radiation of a particular wavelength at a particular temperature. A counterfeit security card will not exhibit that property. Also, a consumer of a product (e.g., a pharmaceutical product) provided in a package using the thermally convertible material of the present invention can test the authenticity of the package by testing its response to the thermal reactive properties of a temperature change. Packages that do not respond properly are considered counterfeit, while packages exhibiting that property will be considered authentic. Other consumer products that may include the composite photonic crystals of the present invention, for example, on the housing of a manufactured product (e.g., an electronic device) or on the surface of an article of apparel (e.g., a shoe). These examples of products for authentication and temperature response through the use of the materials of the present invention therein should not be limited. A product for authentication may include a composite photonic crystal exhibiting a temperature response, which may be used as an indication of the authenticity of the product.

The composite photonic crystal may further be at least partially covered by a coating composition in a multilayer structure. In one embodiment, the composite photonic crystal is coated with the "hard coat" coating composition described above. In another embodiment, the composite photonic crystal is coated with an anti-reflective coating, for example in a multilayer anti-reflective stack. The anti-reflective coating may be formed of a dielectric material, e.g., a metal oxide, e.g., Zn deposited by sputtering₂SnO₄、In₂SO₄、SnO₂、TiO₂、In₂O₃、ZnO、Si₃N₄And/or Bi₂O₃。

The following examples are given to illustrate the general principles of the invention. The present invention should not be considered limited to the particular examples described. All parts are by weight unless otherwise indicated.

Examples

Example 1

The dispersion of polystyrene particles in water was prepared by the following engineering. 2.5 grams (g) of sodium bicarbonate from Aldrich Chemical Company, Inc. was mixed with 2250 grams Deionized (DI) water and 150 grams of ethylene glycol supplied by Aldrich Chemical Company, Inc. and charged to a 5 liter reactor equipped with a thermocouple, heating mantle, stirrer, reflux condenser, and nitrogen inlet. The mixture was purged with nitrogen for 43 minutes with stirring and then surrounded with nitrogen. 10.5 grams of Aerosol MA80-I from Cytec industries, Inc. and 4.0 grams of Brij35 (polyoxyethylene (23) lauryl ether), 1.0 gram of Sodium Styrene Sulfonate (SSS) from Aldrich Chemical Company, Inc. in 25 grams of deionized water were added to the mixture with stirring. The mixture was heated to about 50 ℃ using a heating mantle. Styrene monomer (520 grams) from Aldrich Chemical Company, inc. was added to the kettle with stirring. The mixture was heated to about 65 ℃. Sodium persulfate (6.25 grams in 72 grams of deionized water) from aldrich chemical Company, inc. The temperature was maintained at about 65 ℃ for 6 hours with agitation. A mixture of deionized water (450 grams), Brij35(1.5 grams), sodium persulfate (1.5 grams), styrene (100 grams), methyl methacrylate (100 grams), and sodium styrene sulfonate (1.6 grams), all from Aldrich Chemical Company, inc. The temperature of the mixture was maintained at 65 ℃ for about 2 hours. The resulting polymer dispersion was filtered through a one micron filter bag. The polymer dispersion was then filtered using a 4 inch ultrafiltration chamber with a 2.41 inch polyvinylidene fluoride membrane (both from PTI advanced filtration, inc. oxnard, CA.) and pumped using a peristaltic pump at a flow rate of about 170 milliliters per second. After 3000 grams of ultrafiltrate were removed, deionized water (2985 grams) was added to the dispersion. This exchange was repeated several times until 11349 grams of ultrafiltrate was replaced with 11348 grams of deionized water. Additional ultrafiltrate was then removed until the solid content of the mixture was 44.8% by weight. The material was applied to a 2 mil thick polyethylene terephthalate (PET) substrate by a slot coater from FrontierIndustrial Technology, inc., Towanda, Pa. and dried at 180 ° F for 40 seconds to a dried thickness of about 10 microns. The test was performed using a Cary500 spectrophotometer from Varian, inc, and the resulting material diffracted 657 nm of light.

Example 2

The ultraviolet radiation curable organic composition was prepared by the following procedure. Diphenyl (2,4, 6-trimethylbenzoyl) phosphine oxide/2-hydroxy-2-methylpropiophenone (0.05 g) was mixed with 2 g of CN4000 (an aliphatic methane acrylate from Sartomer Company, inc., Exton, Pa). This uv-curable composition was subsequently applied to the material from example 1 by means of a draw down bar. The coated material was covered with a 1 mil thick PET film (cover sheet), and then subjected to ultraviolet curing with a 100W mercury lamp for 30 seconds. The resulting film was immersed in toluene for 24 hours to remove the polystyrene particles and then dried at room temperature, resulting in an inverse opal structure with a periodic array of voids in the cured matrix.

The voids in the inverse opal were infiltrated with a mixture of diphenyl (2,4, 6-trimethylbenzoyl) phosphine oxide/2-hydroxy-2-methylpropiophenone (0.05 g), stearyl acrylate (2 g SR257), and polyethylene glycol (400) dimethacrylate (0.04 g, SR603) (both from Sartomer Company, inc., Exton, Pa.). The filled inverse opal was cured with ultraviolet light for 30 seconds using a 100W mercury lamp. The temperature response of the diffraction of the resulting film is shown in FIG. 1. The diffraction wavelength red-shifted from 604 nm to 647 nm when the temperature was changed from 10 ℃ to 30 ℃. Upon cooling, the diffracted wavelength reversibly returns to 604 nm.

While the preferred embodiments of the invention have been described above, obvious modifications and variations of the invention can be made without departing from the spirit and scope of the invention. The scope of the invention is defined in the appended claims and equivalents of the appended claims.

Claims (20)

1. A composite photonic crystal comprising:

(i) an inverse opal structure defining an ordered array of voids, and

(ii) a filler composition received by the void, wherein a property of the filler composition changes in response to an excitation, thereby changing a bandgap of radiation reflected by the composite photonic crystal.

2. The composite photonic crystal of claim 1, wherein the filler composition is responsive to temperature changes.

3. The composite photonic crystal of claim 2, wherein the filler composition undergoes a phase change in response to a temperature change.

4. The composite photonic crystal of claim 3, wherein the filler composition comprises a side chain crystalline polymer.

5. The composite photonic crystal of claim 4, wherein the side chain crystalline polymer comprises an acrylic polymer having linear alkyl side chains of at least 8 carbon atoms.

6. The composite photonic crystal of claim 2, wherein the filler composition changes electrical conductivity in response to a change in temperature.

7. The composite photonic crystal of claim 2, wherein the refractive index difference between the inverse opal structure and the filler composition changes in response to temperature changes.

8. The composite photonic crystal of claim 2, wherein the filler composition expands in response to a change in temperature.

9. A method of detecting a change in temperature, comprising:

providing a composite photonic crystal comprising: (i) an inverse opal structure defining an ordered array of voids, and (ii) a filler composition received by the voids, wherein a property of the filler composition changes in response to a change in temperature;

changing the temperature of the composite photonic crystal; and

and detecting the change of the photonic band gap of the composite photonic crystal.

10. The method of claim 9, wherein the filler composition undergoes a phase change in response to a change in temperature of the composite photonic crystal.

11. The method of claim 9, wherein the filler composition comprises a side chain crystalline polymer.

12. The method of claim 9, wherein the detected change is a change in intensity of radiation reflected by the composite photonic crystal.

13. The method of claim 9, wherein the detectable change is a change in wavelength of radiation reflected by the composite photonic crystal.

14. A method of controlling the wavelength of radiation reflected by a surface, comprising:

applying the composite photonic crystal of claim 1 to at least a portion of a surface of a substrate;

exposing the substrate surface with the composite photonic crystal to radiation at an exposure temperature such that the composite photonic crystal reflects a wavelength band of radiation at the exposure temperature.

15. The method of claim 13, wherein the reflected wavelength band comprises infrared radiation.

16. The method of claim 13, wherein the reflected wavelength band includes visible radiation.

17. A method of fabricating a temperature responsive composite photonic crystal, comprising:

preparing a reverse opal defining a plurality of voids;

filling the void with a polymerizable filler composition; and

polymerizing the filler composition, wherein a property of the filler composition changes in response to a change in temperature, thereby changing a bandgap of radiation reflected by the composite photonic crystal.

18. The method of claim 17, wherein the polymerized filler composition undergoes a phase change in response to a change in temperature.

19. The method of claim 18, wherein the filler composition comprises a side chain crystalline polymer.

20. The method of claim 19, wherein the polymerizable filler composition is uv curable.