Photonic crystals, methods of making and using the same

Abstract

The application discloses a photonic crystal and a preparation method and application thereof. The preparation method of the photonic crystal comprises the following steps: applying a reaction solution on a surface of a base material, and performing a photopolymerization reaction under the conditions of a magnetic field and light to obtain the photonic crystal; wherein the reaction solution comprises magnetic nanoparticles, a reaction monomer, a photoinitiator and a solvent. The preparation method of the photonic crystal can obtain the photonic crystal based on the magnetic nanoparticles through a magnetic induction self-assembly mode, and the photonic crystal has good easy-to-pattern characteristics and clear structural color.

Description

Technical Field

[0001] This invention relates to a photonic crystal, its preparation method, and its applications. Background Technology

[0002] Photonic crystals are crystalline materials with periodically varying refractive indices and photonic bandgap characteristics. Their manipulability of light propagation and the advantages of photons in response, storage, information processing, and capacity endow them with enormous application potential as "optical semiconductors." Currently, methods for fabricating photonic crystal microarrays mainly include colloidal self-assembly technology, inkjet printing technology, 3D printing technology based on micro-stereolithography or two-photon polymerization, and patterned surface-assisted self-assembly technology. Among them, colloidal self-assembly technology is a widely used photonic crystal preparation technology. The preparation process is relatively simple, but the photonic crystal structure prepared is relatively simple and unstable. Inkjet printing can realize the construction of micro- and nano-scale photonic crystals. However, the structure and precision of the prepared micro-arrays change with the wettability, rheology, temperature and droplet surface tension of the substrate. Micro-stereolithography-based 3D printing technology can realize the construction of micro- and nano-scale photonic crystal micro-arrays with complex structures. However, the material systems applicable to this technology are relatively limited. Two-photon polymerization-based 3D printing technology can also prepare photonic crystal micro-arrays with complex micro- and nano-scale structures. However, this technology has expensive equipment and low universality.

[0003] With the development of surface patterning technology and the innovative applications of patterned surfaces, the method of preparing photonic crystal microarrays by inducing confined self-assembly of colloidal nanoparticles using the differences in physical or chemical properties of different regions of a patterned surface has attracted much attention. Preparing polymer brush micropatterns with contrasting physical or chemical properties on a substrate surface using patterning technology is an important means of constructing patterned surfaces. However, existing preparation methods suffer from difficulties in controlling the chemical composition and structure of photonic crystals, and the inability to achieve high-precision 3D photonic crystal microarrays with complex structures. Further exploration is needed in preparation methods and processes. In recent years, research on controlling the structure and properties of photonic crystals using external fields (such as electric and magnetic fields) has gradually unfolded. Among these, the inherent properties of magnetic nanoparticles allow for precise control of their spatial distribution in the preparation system through the action of an external magnetic field. However, in existing technologies, when magnetic nanoparticles are used to prepare photonic crystals, the resulting photonic crystals have a simple composition and structure, making it difficult to obtain photonic crystals with clear structural colors and easy patterning. Furthermore, their responsiveness to solvents is poor, making them difficult to control. Summary of the Invention

[0004] To address the shortcomings of existing photonic crystal technologies, such as difficulties in controlling the structure and properties and complex fabrication methods, this invention provides a photonic crystal, its fabrication method, and its applications. The photonic crystal fabrication method of this invention allows for the convenient and efficient preparation of photonic crystals based on magnetic nanoparticles through magnetically induced self-assembly. This photonic crystal exhibits excellent patterning properties and clear structural color.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0006] This invention provides a method for preparing a photonic crystal, which includes the following steps:

[0007] The reaction solution is applied to the surface of the matrix material, and a photopolymerization reaction is carried out under magnetic field and light conditions to obtain the photonic crystal.

[0008] The reaction solution comprises magnetic nanoparticles, a reactive monomer, a photoinitiator, and a solvent.

[0009] In some embodiments, the photonic crystal is a multi-component photonic crystal, and the fabrication method of the multi-component photonic crystal includes the following steps:

[0010] The first reaction solution was applied to the surface of the matrix material, and a photopolymerization reaction was carried out under magnetic field and light conditions to obtain the first photonic crystal.

[0011] The second reaction solution is applied to the surface of the first photonic crystal, and a photopolymerization reaction is carried out under magnetic field and light conditions to obtain the second photonic crystal.

[0012] This process continues until the nth reaction solution is applied to the surface of the (n-1)th photonic crystal, and a photopolymerization reaction is carried out under magnetic field and light conditions to obtain the nth photonic crystal; where n is greater than or equal to 2.

[0013] Thus, the multi-component photonic crystal is obtained;

[0014] The nth reaction solution comprises nth magnetic nanoparticles, nth reaction monomers, nth photoinitiator, and nth solvent.

[0015] In some specific embodiments, the photonic crystal is a two-component photonic crystal, and the preparation method of the two-component photonic crystal includes the following steps:

[0016] The first reaction solution is applied to the surface of the substrate material, and a photopolymerization reaction is carried out under magnetic field and light conditions to obtain the first photonic crystal; the second reaction solution is applied to the surface of the first photonic crystal, and a photopolymerization reaction is carried out under magnetic field and light conditions to obtain the second photonic crystal; thus, the bicomponent photonic crystal is obtained.

[0017] The first reaction solution comprises first magnetic nanoparticles, first reaction monomers, first photoinitiator, and solvent;

[0018] The second reaction solution comprises a second magnetic nanoparticle, a second reaction monomer, a second photoinitiator, and a second solvent.

[0019] In this invention, the solvent can be a solvent conventionally used in the art, preferably an alcohol solvent. For example, the alcohol solvent is ethanol.

[0020] In this invention, the particle size of the magnetic nanoparticles is preferably 60-80 nm.

[0021] In this invention, the magnetic nanoparticles can be magnetic nanoparticles conventionally used in the art, preferably selected from Fe3O4 particles and / or Co3O4 particles.

[0022] In some embodiments, the magnetic nanoparticles are Fe3O4 particles.

[0023] The preparation method of the Fe3O4 particles can be a conventional preparation method in the art, and preferably includes the following steps:

[0024] The ferric salt, reducing agent, dispersant and solvent are mixed to obtain a mixture. The mixture is then mixed with an alkali and reacted to obtain the Fe3O4 particles.

[0025] The ferric salt is preferably one or more of ferric chloride, ferric citrate, ferric acetate, ferric nitrate, and ferric sulfate, for example, ferric chloride.

[0026] The reducing agent is preferably one or more of ascorbic acid, citric acid, glucose, oxalic acid, sodium sulfite, sodium thiosulfate, and sodium borohydride, for example, ascorbic acid.

[0027] The dispersant is, for example, sodium poly(4-styrenesulfonic acid-copolymer-maleic acid).

[0028] The mixing temperature is preferably 40-60°C, for example, 50°C.

[0029] The mixing time is preferably 30-60 minutes, for example, 40 minutes.

[0030] The mixing is preferably carried out under magnetic stirring.

[0031] The reaction temperature is preferably 150-200°C, for example 190°C.

[0032] The reaction time is preferably 7-15 hours, for example, 9 hours.

[0033] The reaction is preferably carried out under magnetic stirring.

[0034] The base is preferably an alkali metal hydroxide, such as NaOH.

[0035] In some preferred embodiments, the magnetic nanoparticles are magnetic nanoparticles coated with SiO2.

[0036] The particle size of the magnetic nanoparticles coated with SiO2 is preferably 100-120 nm, for example, 105 nm, 113 nm or 116 nm.

[0037] The method for preparing the SiO2-coated magnetic nanoparticles preferably includes the following steps: a third mixing of a dispersion containing uncoated magnetic nanoparticles, ammonia, and a solvent to obtain a first mixture; a fourth mixing of the first mixture and a silicon source solution to obtain a second mixture; and the addition of an electrolyte aqueous solution to the second mixture, followed by magnetic separation, washing, and drying to obtain the final product. Preferably, the solvent is an alcohol solvent, such as ethanol; and the electrolyte in the electrolyte aqueous solution preferably includes one or more of sodium chloride, potassium chloride, sodium nitrate, and sodium sulfate.

[0038] In some embodiments, the temperature of the third mixture is 45-60°C, for example, 50°C.

[0039] In some embodiments, the temperature of the fourth mixing is 45-60°C, for example, 50°C.

[0040] In some embodiments, the silicon source solution comprises a silicon source and an alcohol solvent. The silicon source is preferably tetraethyl silicate. The alcohol solvent is preferably ethanol.

[0041] The volume ratio of the silicon source to the alcohol solvent is preferably 1:(8-15), for example, 1:10.

[0042] In some embodiments, the mass fraction of the electrolyte aqueous solution is 2%-3%, for example 2.5%, where the percentage is the mass percentage of the electrolyte in the electrolyte aqueous solution.

[0043] In this invention, the reactive monomer can be a conventional reactive monomer capable of photopolymerization in the art, preferably selected from one or more of methacrylates, acrylates, acrylamides, acrylic acid and acrylonitrile and their prepolymers, such as polyethylene glycol diacrylate.

[0044] In this invention, the photoinitiator can be a photoinitiator conventionally used in the art, preferably including one or more of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, 2,4-diethylthioxanthone, and 2-hydroxy-2-methyl-1-phenyl-1-propanone, for example, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.

[0045] In this invention, the mass ratio of the magnetic nanoparticles to the reactive monomers is preferably 1:(250-300).

[0046] In this invention, the mass ratio of the reactive monomer to the photoinitiator is preferably (15-25):1, for example, 22.4:1.

[0047] In this invention, after the photopolymerization reaction under magnetic field and light conditions, a washing step is generally included. The washing agent preferably includes water and / or an alcohol solvent. The alcohol solvent is, for example, ethanol.

[0048] In some embodiments, the method for preparing the reaction solution includes the following steps:

[0049] The magnetic nanoparticle dispersion and the reactive monomer are first mixed to obtain a monomer dispersion; the initiator solution and the monomer dispersion are second mixed to obtain the final product; wherein the initiator solution includes a photoinitiator and a solvent; and the magnetic nanoparticle dispersion includes magnetic nanoparticles and a solvent.

[0050] The temperature of the first mixture is preferably 50-70°C, for example, 60°C.

[0051] The mixing time for the first mixing is preferably 3-5 hours, for example, 4 hours.

[0052] In this invention, the matrix material can be any matrix material conventionally used in the art, and the material of the matrix material is not particularly limited, and can be glass, metal, or plastic. The surface shape of the matrix material is also not particularly limited, and can be a planar material or a curved material, a rigid material or a flexible material.

[0053] In some embodiments, the substrate material is selected from glass sheets, metal sheets, or plastic sheets, such as glass sheets.

[0054] In this invention, the application method is preferably coating.

[0055] During the coating process, the coating thickness of the reaction solution is preferably 0.2-0.4 mm, for example, 0.2-0.3 mm.

[0056] In this invention, the magnetic field and the illumination can be obtained using a magnetic field-assisted digital micromirror device (DMM) optical modulation system. The magnetic field-assisted DMM optical modulation system generally includes a digital micromirror device optical modulation system and a magnetic field system. The digital micromirror device optical modulation system preferably includes a light source, a homogenizing and collimating optical element, a digital micromirror device spatial light modulator and its controller, and a projection lens. The magnetic field system preferably includes a permanent magnet.

[0057] In this invention, the illumination time is preferably 180s or more, and more preferably 180-190s.

[0058] In this invention, the wavelength of the light source used for illumination is preferably 430-470nm, for example, 450nm. Preferably, the power of the light source is 5-15W, for example, 10W.

[0059] In this invention, the strength of the magnetic field is preferably 400-1320 Gs, for example 407.3 Gs, 765.1 Gs, 1023.8 Gs, 1044.0 Gs or 1317.8 Gs.

[0060] In this invention, the photopolymerization time is preferably 180s or more, and more preferably 180-190s.

[0061] This invention provides a photonic crystal, which is prepared by the photonic crystal preparation method described above.

[0062] The structural color of the photonic crystal is preferably yellow-green, blue-green, purple, blue, orange, yellow, or khaki.

[0063] In some implementations, the photonic crystal is a single-component photonic crystal.

[0064] In some implementations, the photonic crystal is a multi-component photonic crystal.

[0065] In some specific implementations, the photonic crystal is a two-component photonic crystal.

[0066] The present invention also provides an application of the photonic crystal described above in dynamic monitoring, color display, or information anti-counterfeiting.

[0067] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0068] The reagents and raw materials used in this invention are all commercially available.

[0069] The positive and progressive effects of this invention are as follows:

[0070] The photonic crystal fabrication method of this invention can conveniently and efficiently prepare photonic crystals based on magnetic nanoparticles through magnetically induced self-assembly. These photonic crystals exhibit excellent patterning properties and clear structural colors. Furthermore, by rationally designing the composition of the photonic crystal, photonic crystals with good solvent responsiveness can also be obtained. Moreover, when using DMD optical modulation technology, the macroscopic and microscopic structures of the photonic crystal can be synergistically controlled by simultaneously controlling the DMD optical modulation parameters and magnetic field parameters, thereby obtaining photonic crystals with complex structures and functions. Attached Figure Description

[0071] Figure 1 This is a schematic diagram of a magnetic field-assisted DMD optical modulation system. In the diagram, 101 is the light source, 102 is the homogenizing and collimating optical element, 102-2 is the digital grayscale image, 101-2 is the computer, 103 is the DMD spatial light modulator, 104 is the controller, 105 is the projection lens, 106 is the substrate material, and 107 is the permanent magnet.

[0072] Figure 2 This is a schematic diagram of the process for fabricating photonic crystal patterns using a magnetic field-assisted DMD optical modulation system in Example 1. The arrows indicate the fabrication process. In the diagram, 201 represents the substrate material, 202 the monomer, 203 the photoinitiator, 204 the magnetic nanoparticles, 205 the patterned beam, 206 the magnetic field, and 207 the photonic crystal.

[0073] Figure 3 ① is a digital image of the photonic crystal prepared using Fe3O4@SiO2 with a particle size of 116 nm in Example 1. Figure 3 ② is a digital image of the photonic crystal prepared using Fe3O4@SiO2 with a particle size of 113 nm in Example 1. Figure 3 ③ is a digital image of the photonic crystal prepared using Fe3O4@SiO2 with a particle size of 105 nm in Example 1.

[0074] Figure 4 The image shows a SEM image of the photonic crystal obtained in Example 1 (using Fe3O4@SiO2 with a particle size of 116 nm).

[0075] Figure 5This is a schematic diagram of the preparation of a two-component photonic crystal in Example 2, with the arrows indicating the preparation process. ① represents a substrate material covered with a reaction solution 1 containing monomer 1; ② represents a schematic diagram of the preparation of the first-component photonic crystal under the influence of a patterned beam and magnetic field generated by a DMD optical modulation system, where the patterned area is the illuminated area; ③ represents a schematic diagram of the pattern of the prepared first-component photonic crystal; ④ represents a schematic diagram of the preparation of the second-component photonic crystal under the influence of a patterned beam and magnetic field generated by a DMD optical modulation system, where the entire surface is the illuminated area; ⑤ represents a schematic diagram of the prepared two-component photonic crystal; and ⑥ represents a schematic diagram of the two-component photonic crystal developing color in ethanol.

[0076] Figure 6 ① and ② are digital images of the two-component photonic crystal prepared in Example 2 and its color development in ethanol, respectively.

[0077] Figure 7 This is a schematic diagram of the preparation of photonic crystal patterns with different structural colors in Example 3. The arrows indicate the preparation process. ① to ④ are schematic diagrams of the preparation methods of four photonic crystals obtained by applying magnetic fields 1, 2, 3 and 4, respectively. The reaction regions have the same pattern shape but different positions, and the central magnetic field strength of magnetic fields 1, 2, 3 and 4 gradually increases.

[0078] Figure 8 Figures ① to ④ in Example 3 are schematic diagrams showing the ring-shaped ultraviolet rays used at different locations after applying magnetic fields 1, 2, 3, and 4. Figure 8 Image ⑤ is a digital image of the circular photonic crystals with different structural colors prepared in Example 3. Detailed Implementation

[0079] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0080] The specific sources of the reagents used in Examples 1-3 are as follows:

[0081] Polyethylene glycol diacrylate, PEGDA, Maclean Chemicals Co., Ltd., Mw≈200;

[0082] Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, TPO, Maclean Chemical Reagent Co., Ltd., ≥97%;

[0083] Hydroxyethyl methacrylate, HEMA, Maclean Chemical Reagent Co., Ltd., ≥99.0%;

[0084] Figure 1 This diagram illustrates the magnetic field-assisted DMD optical modulation system used in Examples 1, 2, and 3 for fabricating photonic crystals. In this system, 101 is the light source, 102 is the homogenizing and collimating optical element, 102-2 is the digital grayscale image, 101-2 is the computer, 103 is the DMD spatial light modulator, 104 is the controller, 105 is the projection lens, 106 is the substrate material, and 107 is the permanent magnet. The relevant parameters of the components are as follows: Light source: LED lamp, wavelength 453nm, power 20W; DMD spatial light modulator: Texas Instruments, DLP6500; Projection lens: 24-85mm, f / 2.8-4; Permanent magnet: Neodymium iron boron type, magnetic field strength range 407.3-1317.8 Gs.

[0085] The specific parameters of the light source obtained after modulation by the DMD optical modulation system in Examples 1-3 are: wavelength 450nm, power 10W.

[0086] In the following examples, the synthesis method of Fe3O4@SiO2 (particle size 105 nm) includes the following steps:

[0087] S1. Synthesis of Fe3O4 nanoparticles: (1) Add 40 mL of ethylene glycol (EG), 0.65 g of FeCl3, 3.0 g of NaAc, 20 mg of VC, 1.1 g of sodium poly(4-styrenesulfonic acid-copoly-maleic acid) (PSSMA) and an appropriate amount of H2O (30 μL) to a conical reaction flask and seal it. Stir magnetically at 50°C for 40 min until the material is completely dissolved to form a dark green solution; (2) Add 0.6 g of NaOH to the obtained solution and continue stirring until the NaOH is completely dissolved to obtain a reddish-brown and slightly transparent solution. React it at 190°C for 9 h; (3) After the reaction is completed, the supernatant is discarded by magnetic adsorption and the obtained black precipitate is washed three times with 50 mL of 1:1 ethanol / water mixture. Then disperse it in 80 mL of deionized water to obtain a superparamagnetic Fe3O4 nanoparticle aqueous dispersion.

[0088] S2. Coating SiO2 onto the surface of Fe3O4 nanoparticles:

[0089] (1) Add 12 mL of the above-obtained Fe3O4 nanoparticle aqueous dispersion to 80 mL of ethanol, sonicate for 30 min, add 5 mL of NH3•H2O, and continue sonicating for 10 min to form a mixed solution; (2) Transfer the obtained mixed solution to a 500 mL round bottom flask, place the flask in a 50℃ water bath and stir at 750 rpm, mix tetraethyl silicate (TEOS) and ethanol at a volume ratio of 1:10, and inject 4 mL of TEOS / ethanol mixture into the flask every 20 minutes; (3) Add the obtained solution to a 2.5 wt% NaCl solution, stir thoroughly mechanically, and then use magnetic separation to remove the precipitate. Wash the obtained precipitate three times with ethanol and dry it at 60℃ to obtain Fe3O4@SiO2 with a core-shell structure (particle size of 105 nm).

[0090] In the following examples, the method for synthesizing Fe3O4@SiO2 (particle size of 113 nm) differs from the method for synthesizing Fe3O4@SiO2 (particle size of 105 nm) as follows: in step S1, step (1) of synthesizing Fe3O4 nanoparticles, the amount of H2O used is 15 μL.

[0091] In the following examples, the method for synthesizing Fe3O4@SiO2 (particle size of 116 nm) differs from the method for synthesizing Fe3O4@SiO2 (particle size of 105 nm) as follows: in step S1, step (1) of synthesizing Fe3O4 nanoparticles, the amount of H2O used is 0 μL.

[0092] Example 1: Preparation of single-component photonic crystals with different structural colors (based on Fe3O4@SiO2 with different particle sizes)

[0093] Figure 2 This is a schematic diagram of the fabrication process of a photonic crystal using a magnetic field-assisted DMD optical modulation system in Example 1. The arrows indicate the fabrication process. In the diagram, 201 represents the substrate material (18mm × 18mm glass sheet), 202 represents the monomer PEGDA, 203 represents the photoinitiator TPO, 204 represents the magnetic nanoparticles Fe3O4@SiO2, 205 represents the patterned light beam, 206 represents the magnetic field, and 207 represents the photonic crystal.

[0094] The photonic crystal 207 is fabricated on the surface of the substrate material 201 according to the following steps:

[0095] (1) Preparation of reaction solution: Dissolve 100 mg of photoinitiator 203 in 1 mL of anhydrous ethanol and shake for 5 min to obtain initiator solution; Mix 3 mL of magnetic nanoparticle 204 dispersion (prepared by dissolving 0.15-0.18 g of dried Fe3O4@SiO2 particles in 60 mL of ethanol) with 2 mL of monomer 202 and stir thoroughly, and heat at 60 °C for 4 hours; Mix the above two solutions to obtain gray-brown Fe3O4@SiO2 / PEGDA reaction solution.

[0096] (2) The above-obtained reaction solution is coated onto the surface of the substrate material 201 (glass slide) and placed on the projection plane of the magnetic field-assisted DMD light modulation system (coating thickness is 0.2-0.3 mm). On one hand, the DMD light modulation system forms a patterned beam 205 with contrast between illuminated and unilluminated areas on the surface of the substrate material 201, corresponding to the digital image design; on the other hand, a magnetic field 206 (magnetic field strength is 1023.8 Gs) is generated under the action of a permanent magnet, causing the magnetic nanoparticles 204 in the reaction solution to be arranged in an orderly manner; when the patterned beam 205 acts on the surface of the reaction solution where the magnetic nanoparticles are arranged in an orderly manner (illumination time is 180-190 s), in the illuminated area, the reactive monomers 202 in the reaction solution undergo photopolymerization under the action of the photoinitiator 203 to generate a photonic crystal containing ordered magnetic nanoparticles. Since the photonic crystal is generated only in the area selected for exposure of the beam image, a patterned photonic crystal 207 is obtained. After the reaction is completed, the obtained sample is thoroughly washed with anhydrous ethanol and deionized water.

[0097] Among them, using magnetic nanoparticles of different sizes can yield photonic crystals of different colors, such as... Figure 3 As shown. Figure 3 ① is a digital image of the photonic crystal prepared using Fe3O4@SiO2 with a particle size of 116 nm in Example 1 (the image was taken directly under natural light, and the same applies below). Figure 3 ② is a digital image of the photonic crystal prepared using Fe3O4@SiO2 with a particle size of 113 nm in Example 1. Figure 3 ③ is a digital image of the photonic crystal prepared using Fe3O4@SiO2 with a particle size of 105 nm in Example 1.

[0098]

[0099] The morphology of the photonic crystal obtained using Fe3O4@SiO2 with a particle size of 116 nm was characterized using scanning electron microscopy, and the resulting SEM images are shown below. Figure 4 As shown.

[0100] The scanning electron microscope used was a Zeiss GeminiSigma 300 VP SEM high-resolution field emission scanning electron microscope from Carl Zeiss AG (ZEISS), Germany. The main parameters were as follows: resolution: SE: 1.0 nm (15 kV), 1.6 nm (1 kV); accelerating voltage: 3 kV; electron gun: Schottky thermal field emission electron gun; electron beam current: maximum beam current not less than 20 nA; magnification: 20000.

[0101] Example 2: Preparation of two-component photonic crystals (based on reaction solutions with different formulations)

[0102] The matrix material is an 18mm × 18mm glass slide; reaction solution 1 contains reaction monomer 1 (PEGDA), photoinitiator 1 (TPO) and magnetic nanoparticles (Fe3O4@SiO2, with a particle size of 113nm); reaction solution 2 contains reaction monomer 2 (HEMA), photoinitiator 2 (2-hydroxy-2-methyl-1-phenyl-1-propanone) and magnetic nanoparticles Fe3O4@SiO2 (with a particle size of 113nm).

[0103] The preparation method of reaction solution 1 is the same as in Example 1. The preparation method of reaction solution 2 is as follows: 3 mL of magnetic nanoparticle dispersion is mixed with 2 mL of monomer 2 and heated at 80°C for 30 min. Then, initiator 2 is added to the above solution and sonicated for 10 min to obtain Fe3O4@SiO2 / HEMA reaction solution.

[0104] Figure 5This diagram illustrates the two-step preparation of a bicomponent photonic crystal in Example 2, with arrows indicating the preparation process. The specific steps are as follows: First, reaction solution 1 is dropped onto the surface of the substrate material and placed on the projection plane of the magnetic field-assisted DMD optical modulation system (200 μL of reaction solution 1 is added, with a coating thickness of 0.2-0.3 mm). Magnetic field 1 is applied to cause the magnetic nanoparticles to align regularly in reaction solution 1. Then, a digital grayscale image containing a "grape" pattern is converted into a digital bitmap file using a computer and loaded into the DMD controller to control the deflection of the DMD micromirrors to achieve light modulation and generate a corresponding beam image (the pattern area is the illuminated area). This triggers a polymerization reaction in the reaction solution on the substrate material surface (illumination time is 180-190 s), resulting in the first component photonic crystal pattern. Next, reaction solution 2 is dropped onto the same substrate material surface and placed at the same position on the projection plane of the magnetic field-assisted DMD optical modulation system (200 μL of reaction solution 1 is added, with a coating thickness of 0.2-0.3 mm). Magnetic field 1 (magnetic field strength 1023.8) is applied. Gs) causes magnetic nanoparticles to align regularly in reaction solution 2. Then, a patternless digital grayscale image is converted into a digital bitmap file and loaded into a DMD controller to control the deflection of the DMD micromirrors, achieving light modulation to generate a corresponding beam image (the entire surface is illuminated). This triggers a polymerization reaction in the reaction solution on the substrate surface (illumination time is 180-190 s), yielding a second-component (PHEMA) photonic crystal film. The prepared material is then removed from the substrate surface to obtain the photonic crystal.

[0105] Figure 6 ① and ② are digital images of the bicomponent photonic crystal prepared in Example 2 and its color development in ethanol, respectively. Since the two components of the photonic crystal were prepared using the same nanoparticles and magnetic field strength, they exhibited the same color in the initial state. Then, the photonic crystal was placed in an ethanol solution. Because the PHEMA polymer absorbs ethanol and expands, the spacing between its internal nanoparticles increases, which in turn causes a red shift in its surface structural color. However, the structure of the PEGDA polymer does not change in the ethanol solution, and its surface structural color remains unchanged.

[0106]

[0107] Example 3: Fabrication of single-component photonic crystal patterns with different structural colors (based on different magnetic field strengths)

[0108] The matrix material is an 18mm × 18mm glass slide; the reaction solution contains a reactive monomer (PEGDA), a photoinitiator (TPO), and magnetic nanoparticles (Fe3O4@SiO2, with a particle size of 116nm); the preparation method of the reaction solution is the same as in Example 1.

[0109] Figure 7This is a schematic diagram of the preparation of multicolor photonic crystal patterns in Example 3. The arrows indicate the preparation process.

[0110] The specific steps are as follows: First, a reaction solution is dropped onto the surface of the substrate material and placed on the projection plane of a magnetic field-assisted DMD light modulation system (the coating thickness of the reaction solution is 0.2-0.3 mm). Magnetic field 1 is applied, followed by irradiation with ring-shaped ultraviolet light emitted from the DMD-based projection system (irradiation time is 180-190 s), causing cross-linking and thus creating an orange circular hydrogel pattern. Then, magnetic field 2 is applied, followed by irradiation with ring-shaped ultraviolet light (irradiation time is 180-190 s), creating a hydrogel pattern with a yellow structural color. After applying magnetic field 3, ring-shaped ultraviolet light is used for irradiation (irradiation time is 180-190 s), and after applying magnetic field 4, ring-shaped ultraviolet light is used for irradiation (irradiation time is 180-190 s), resulting in yellow-green and khaki photonic crystal patterns, respectively. Using this patterning method, a series of multicolored circular patterns with different structural colors can be obtained.

[0111] Figure 8 ①~④ are schematic diagrams showing the ring-shaped ultraviolet rays used at different locations after applying magnetic fields 1, 2, 3 and 4 in Example 3. Figure 8 ⑤ is a digital image of the circular multicolor photonic crystal prepared in Example 3.

[0112]

[0113] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for preparing a photonic crystal, characterized in that, It includes the following steps: The reaction solution is applied to the surface of the matrix material, and a photopolymerization reaction is carried out under magnetic field and light conditions to obtain the photonic crystal. The reaction solution comprises magnetic nanoparticles, a reactive monomer, a photoinitiator, and a solvent.

2. The method for preparing a photonic crystal as described in claim 1, characterized in that, The magnetic nanoparticles are selected from Fe3O4 particles and / or Co3O4 particles; And / or, the magnetic nanoparticles have a particle size of 60-80 nm; And / or, the reactive monomer is selected from one or more of methacrylates, acrylates, acrylamides, acrylic acid and acrylonitrile and their prepolymers, such as polyethylene glycol diacrylate; And / or, the photoinitiator comprises one or more of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, 2,4-diethylthioxanthone, and 2-hydroxy-2-methyl-1-phenyl-1-propanone, for example, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide; And / or, the mass ratio of the magnetic nanoparticles to the reactive monomers is 1:(250-300). And / or, the solvent is an alcohol solvent, such as ethanol; And / or, the mass ratio of the reactive monomer to the photoinitiator is (15-25):1, for example, 22.4:1; And / or, the matrix material is selected from glass sheets, metal sheets or plastic sheets, for example, glass sheets; And / or, the application is performed by coating; wherein, during the coating process, the coating thickness of the reaction solution is preferably 0.2-0.4 mm, for example 0.2-0.3 mm.

3. The method for preparing a photonic crystal as described in claim 2, characterized in that, The magnetic nanoparticles are Fe3O4 particles, and the preparation method of the Fe3O4 particles includes the following steps: The ferric salt, reducing agent, dispersant and solvent are mixed to obtain a mixture. The mixture is then mixed with an alkali and reacted to obtain the Fe3O4 particles. The ferric salt is preferably one or more of ferric chloride, ferric citrate, ferric acetate, ferric nitrate, and ferric sulfate, for example, ferric chloride; The reducing agent is preferably one or more of ascorbic acid, citric acid, glucose, oxalic acid, sodium sulfite, sodium thiosulfate and sodium borohydride, for example, ascorbic acid; The dispersant is, for example, sodium poly(4-styrenesulfonic acid-copolymer-maleic acid); The mixing temperature is preferably 40-60°C, for example, 50°C; The mixing time is preferably 30-60 minutes, for example, 40 minutes; The mixing is preferably carried out under magnetic stirring; The reaction temperature is preferably 150-200°C, for example 190°C; The reaction time is preferably 7-15 hours, for example, 9 hours; The reaction is preferably carried out under magnetic stirring; Preferably, the base is an alkali metal hydroxide, such as NaOH.

4. The method for preparing a photonic crystal as described in claim 1, characterized in that, The method for preparing the reaction solution includes the following steps: A magnetic nanoparticle dispersion and a reactive monomer are first mixed to obtain a monomer dispersion; an initiator solution and the monomer dispersion are second mixed to obtain the desired product; wherein, the initiator solution includes a photoinitiator and a solvent; and the magnetic nanoparticle dispersion includes magnetic nanoparticles and a solvent. And / or, the temperature of the first mixture is 50-70°C, for example, 60°C; And / or, the first mixing time is 3-5 h, for example, 4 h.

5. The method for preparing a photonic crystal as described in claim 1, characterized in that, The magnetic nanoparticles are magnetic nanoparticles coated with SiO2; the particle size of the magnetic nanoparticles coated with SiO2 is preferably 100-120 nm, for example 105 nm, 113 nm or 116 nm.

6. The method for preparing a photonic crystal as described in claim 5, characterized in that, The method for preparing the SiO2-coated magnetic nanoparticles includes the following steps: a third mixing of a dispersion containing uncoated magnetic nanoparticles, ammonia, and an alcohol solvent to obtain a first mixture; a fourth mixing of the first mixture and a silicon source solution to obtain a second mixture; and the addition of an electrolyte aqueous solution to the second mixture, followed by magnetic separation, washing, and drying to obtain the final product. Preferably, the solvent is an alcohol solvent, such as ethanol; and the electrolyte aqueous solution preferably contains one or more of sodium chloride, potassium chloride, sodium nitrate, and sodium sulfate. The temperature of the third mixing step is 45-60°C, for example, 50°C; The temperature of the fourth mixing step is 45-60°C, for example, 50°C; Preferably, the silicon source solution comprises a silicon source and an alcohol solvent; the silicon source is preferably tetraethyl silicate; the volume ratio of the silicon source to the alcohol solvent is preferably 1:(8-15), for example 1:10; and preferably, the alcohol solvent is ethanol. The electrolyte aqueous solution has a mass fraction of 2%-3%, for example, 2.5%, where the percentage represents the mass percentage of the electrolyte in the electrolyte aqueous solution.

7. The method for preparing a photonic crystal as described in claim 1, characterized in that, The magnetic field and the illumination are obtained using a magnetic field-assisted digital micromirror device (DMM) optical modulation system; wherein, the magnetic field-assisted DMM optical modulation system includes a digital micromirror device optical modulation system and a magnetic field system; the digital micromirror device optical modulation system preferably includes a light source, a light-diffusing collimating optical element, a digital micromirror device spatial light modulator and its controller, and a projection lens; the magnetic field system preferably includes a permanent magnet; And / or, the illumination time is more than 180s, preferably 180-190s; And / or, the wavelength of the light source used for the illumination is 430-470nm, for example 450nm; preferably, the power of the light source is 5-15W, for example 10W; And / or, the strength of the magnetic field is 400-1320 Gs, for example 407.3 Gs, 765.1 Gs, 1023.8 Gs, 1044.0 Gs or 1317.8 Gs; And / or, the photopolymerization time is 180s or more, preferably 180-190s.

8. A photonic crystal, characterized in that, It is prepared by the method for preparing photonic crystals as described in any one of claims 1-7.

9. The photonic crystal as described in claim 8, characterized in that, The structural color of the photonic crystal is yellow-green, blue-green, purple, blue, orange, yellow, or khaki.

10. An application of the photonic crystal as described in claim 8 or 9 in dynamic monitoring, color display, or information anti-counterfeiting.

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