A self-filmable core-shell structure photonic crystal microsphere and a preparation method thereof

Abstract

This invention discloses a self-forming core-shell photonic crystal microsphere and its preparation method, belonging to the field of materials engineering technology. The invention employs a seed emulsion polymerization method to prepare core-shell composite photonic crystal microspheres with a hard core and a soft shell. The hard core includes hard microspheres with high glass transition temperatures such as PS, PMMA, PAN, and SiO2, while the soft shell mainly includes block copolymers with one or two specific compositions and low glass transition temperatures, such as EA, BA, and MMA. The hard-core, soft-shell photonic crystal microspheres prepared by this invention have a glass transition temperature below room temperature, and can automatically adhere to the hard microspheres after moisture removal, forming a crack-free and smooth film with a certain degree of elasticity, achieving elastic recovery after stretching. Furthermore, when the particle size of the core-shell photonic crystal microspheres is between 200 and 300 nm, the formed film exhibits structural color.

Description

Technical Field

[0001] This invention belongs to the field of materials engineering technology, specifically relating to a self-forming core-shell structured photonic crystal microsphere and its preparation method. Background Technology

[0002] Photonic crystals (PCs) are crystalline materials formed by the periodic arrangement of substances with different refractive indices in space. A key characteristic of photonic crystals is their photonic bandgap, which blocks the propagation of light within a specific frequency range. When the photonic bandgap of a photonic crystal falls within the visible light spectrum, visible light within the bandgap is selectively reflected, resulting in coherent diffraction on the periodically arranged surface of the photonic crystal. The constructive interference of the reflected light stimulates the human eye, producing a structural color effect. Unlike conventional dyes that generate color based on light absorption, photonic crystals produce structural colors derived from their physical structure by modulating light diffraction and scattering. This makes them more environmentally friendly and holds great potential for applications in coloring coatings.

[0003] Traditional photonic crystals, such as polystyrene and silicon dioxide, often crack during the drying process due to weak interparticle forces. Chinese patent document CN115558145A discloses a method for preparing photonic crystal structured color-changing materials using a spray coating method, but the photonic crystal microspheres used show cracks after drying on the substrate surface. This has led to methods for preparing structured color films by combining photonic crystal microspheres with polymer film-forming materials. For example, Chinese patent document CN116622215A provides a method for preparing SiO2-phenolic resin-polyurethane composite photonic crystal deformation-changing films, which combines SiO2 microspheres with resin materials to prepare structured color films. However, this method requires the addition of additional film-forming materials, which affects the self-assembly process of the photonic crystal to form the structured color film, and cracking still occurs in areas where the polymer filling is uneven.

[0004] To address the issue that existing single photonic crystal microspheres are prone to cracking when forming thin films, and to further achieve good film-forming stability of photonic crystal structure color films under external conditions such as stretching and compression, there is an urgent need to develop a photonic crystal microsphere that can directly form crack-free, stretchable, and recoverable thin films. Summary of the Invention

[0005] Technical issues:

[0006] Traditional photonic crystal microspheres, such as PS, PMMA, PAN, and SiO2, are prone to cracking when directly dried to form films, or they are susceptible to film rupture under external forces. When polymer materials are added to assist film formation, the polymer film-forming materials can affect the self-assembly process of the photonic crystal microspheres, causing unevenness in the structural color produced by the microspheres.

[0007] Technical solution:

[0008] To address the aforementioned problems, this invention employs a seed emulsion polymerization method to prepare core-shell composite photonic crystal microspheres with a hard core and a soft shell. The hard core comprises hard microspheres with high glass transition temperatures, such as PS, PMMA, PAN, and SiO2, while the soft shell mainly comprises one or two block copolymers with low glass transition temperatures, such as EA, BA, and MMA. The hard-core, soft-shell photonic crystal microspheres prepared by this invention have a glass transition temperature below room temperature. After moisture removal, they can automatically adhere to the hard microspheres, forming a crack-free and smooth film with a certain degree of elasticity, allowing for elastic recovery after stretching. Furthermore, when the particle size of the core-shell photonic crystal microspheres is between 200 and 300 nm, the resulting film exhibits structural color.

[0009] The first objective of this invention is to provide a core-shell structured photonic crystal microsphere with a hard core and soft shell that can form a self-elastic thin film.

[0010] A second objective of this invention is to provide a method for preparing the core-shell structured photonic crystal microspheres with a hard core and a soft shell.

[0011] Furthermore, the present invention also provides the application of the hard-core soft-shell core-shell structured photonic crystal microspheres in structural color generation.

[0012] To achieve the aforementioned objectives, the present invention employs the following technical solution:

[0013] This invention provides a core-shell structured photonic crystal microsphere, wherein the hard core and soft shell composite structure can be gradually formed into a core-shell structure through seed emulsion polymerization.

[0014] The present invention also provides a method for preparing the core-shell structured photonic crystal microspheres, comprising:

[0015] S1. A portion of the hard core is emulsified with monomer, crosslinking agent, emulsifier, and water, and then an initiator is added to react and obtain a polymer seed emulsion.

[0016] S2. Add another portion of the hard core monomer, crosslinking agent, and initiator to the obtained polymer seed emulsion, and polymerize to obtain a hard core microsphere system;

[0017] S3. Add the soft-shell monomer, crosslinking agent, and initiator to the obtained hard-core microsphere system to initiate polymerization and obtain hard-core soft-shell photonic crystal microspheres.

[0018] In one embodiment of the present invention, the particle size of the polymer seed in S1 is about 120 nm and the polymer dispersibility index (PDI) is less than 0.08.

[0019] In one embodiment of the present invention, the particle size of the hard core microspheres in S2 is about 170-220 nm, and the PDI is less than 0.08.

[0020] In one embodiment of the present invention, the particle size of the hard-core soft-shell photonic crystal microspheres in S2 is about 200-300, and the PDI is less than 0.08.

[0021] In one embodiment of the present invention, the hard core is one or more of styrene (St), methyl methacrylate (MMA), and acrylonitrile (AN).

[0022] In one embodiment of the present invention, the monomer used for the soft shell is selected from:

[0023] ① Ethyl acrylate (EA), or

[0024] ② A combination of ethyl acrylate (EA) and butyl acrylate (BA), or

[0025] ③ A combination of methyl methacrylate (MMA) and butyl acrylate (BA).

[0026] In one embodiment of the present invention, the mass ratio of ethyl acrylate (EA) to butyl acrylate (BA) in the monomer for soft shell is (19-20):(0-1).

[0027] In one embodiment of the present invention, the mass ratio of methyl methacrylate (MMA) to butyl acrylate (BA) in the monomer for the soft shell is 1:3.

[0028] In one embodiment of the present invention, the mass ratio of the hard core monomer in S1 to the hard core monomer in S2 is 1:(1-2). Specifically, 1:1.5 may be selected.

[0029] In one embodiment of the present invention, the emulsifier used for emulsification is one of sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate, and sodium dodecyl sulfonate.

[0030] In one embodiment of the present invention, the emulsifier accounts for 0.15-0.25 wt.% of the total monomer concentration; specifically, 0.2 wt.% is preferred. (Total monomers refer to the total mass of the hard core monomers and the soft shell monomers).

[0031] In one embodiment of the present invention, the crosslinking agent may be one or more of diene crosslinking agents such as divinylbenzene (DVB), allyl methacrylate (ALMA), and isoprene.

[0032] In one embodiment of the present invention, the amount of the crosslinking agent in S1 or S2 relative to the monomer used for hardening the core in this step is 10-14 wt.%.

[0033] In one embodiment of the present invention, the amount of crosslinking agent in S3 is 0.2-1.0 wt.% relative to the monomer used for the soft shell in this step.

[0034] In one embodiment of the present invention, the initiator may also be one or more of ammonium persulfate (APS), potassium persulfate, and sodium persulfate.

[0035] In one embodiment of the present invention, in S1, S2 or S3, the ratio of the initiator to the monomer is 0.5-1 wt.%.

[0036] The present invention also provides the application of the hard-core soft-shell photonic crystal microspheres in structural color-forming thin films.

[0037] The beneficial effects of this invention are:

[0038] The core-shell structured photonic crystal microspheres prepared by this invention require inexpensive monomer raw materials. The glass transition temperatures of the hard core are all above 100°C, allowing the entire core microsphere to maintain its spherical shape at ambient temperature, facilitating its self-assembly into a regular array. The outer shell of the photonic crystal microsphere has a glass transition temperature below room temperature, allowing it to form a thin film at room temperature after moisture removal. This film exhibits good flexibility and flatness, without cracking. The average refractive index of the hard core is higher than that of the outer shell; the refractive index difference between the two can impart high-saturation colors to the formed structural color film, showing broad application prospects in the field of structural color generation. Attached Figure Description

[0039] Figure 1 The particle size distribution curves of PS seeds, PS cores and PS@P(EA-BA) photonic crystal composite microspheres prepared by seed emulsion polymerization according to the present invention are shown.

[0040] Figure 2 The Fourier transform infrared spectrum of the PS@P(EA-BA) photonic crystal composite microspheres of the present invention is shown below.

[0041] Figure 3 A physical image of the flat structured color film formed by the PS@P(EA-BA) photonic crystal composite microspheres prepared in Example 1 of the present invention;

[0042] Figure 4 This is a physical image of the PS core photonic crystal thin film prepared in Comparative Example 1 of the present invention;

[0043] Figure 5 This is a scanning electron microscope image of the PS core photonic crystal thin film prepared in Comparative Example 1 of the present invention;

[0044] Figure 6 This is a scanning electron microscope image of the PS@P(EA-BA) photonic crystal thin film prepared in Example 1 of the present invention;

[0045] Figure 7 The image shows the stretched recovery of the PS@P(EA-BA) photonic crystal thin film prepared in Example 1 of this invention. Detailed Implementation

[0046] To better understand the present invention, the following embodiments are provided to further illustrate the content of the present invention, but the following examples are not intended to limit the present invention.

[0047] Test method:

[0048] Photonic crystal microsphere particle size and monodispersity testing: The samples were tested using a Zetasizer Nano-ZS90 potential and particle size analyzer.

[0049] Example 1:

[0050] (1) Add 5g of St and 0.5g of DVB to 100mL of deionized water containing 0.065g of SDS, emulsify at 300rpm for 30min, then raise the reaction temperature to 85℃ and hold for 10min, then add 0.05g of APS to initiate polymerization for 1h to obtain PS seeds with a particle size of about 120nm.

[0051] (2) Add 7.5g St and 1g DVB to the reaction system, and then add 0.05g APS to initiate polymerization for 1.5h to obtain PS core with a particle size of about 220nm.

[0052] (3) Add 19g EA, 1g BA and 0.04g ALMA to the reaction system, and then add 0.1g APS to initiate polymerization for 1.5h to obtain core-shell structure PS@P(EA-BA) photonic crystal microsphere emulsion with a particle size of about 280nm.

[0053] (4) Take 5 mL of emulsion and drop it onto a petri dish. After drying, it forms a smooth elastic film with structural color.

[0054] Example 2:

[0055] (1) Add 5g of St and 0.5g of DVB to 100mL of deionized water containing 0.066g of SDS, emulsify at 300rpm for 30min, then raise the reaction temperature to 85℃ and hold for 10min, then add 0.05g of APS to initiate polymerization for 1h to obtain PS seeds with a particle size of approximately 120nm.

[0056] (2) Add 7.5g St and 1g DVB to the reaction system, and then add 0.05g APS to initiate polymerization for 1.5h to obtain PS core with a particle size of about 190nm.

[0057] (3) Add 19g EA, 1g BA and 0.04g ALMA to the reaction system, and then add 0.1g APS to initiate polymerization for 1.5h to obtain core-shell structure PS@P(EA-BA) photonic crystal microsphere emulsion with a particle size of about 250nm.

[0058] (4) Take 5 mL of emulsion and drop it onto a petri dish. After drying, it forms a smooth elastic film with structural color.

[0059] Example 3:

[0060] (1) Add 5g of St and 0.5g of DVB to 100mL of deionized water containing 0.070g of SDS, emulsify at 300rpm for 30min, then raise the reaction temperature to 85℃ and hold for 10min, then add 0.05g of APS to initiate polymerization for 1h to obtain PS seeds with a particle size of approximately 120nm.

[0061] (2) Add 7.5g St and 1g DVB to the reaction system, and then add 0.05g APS to initiate polymerization for 1.5h to obtain PS core with a particle size of about 170nm.

[0062] (3) Add 19g EA, 1g BA and 0.04g ALMA to the reaction system, and then add 0.1g APS to initiate polymerization for 1.5h to obtain core-shell structure PS@P(EA-BA) photonic crystal microsphere emulsion with a particle size of about 210nm.

[0063] (4) Take 5 mL of emulsion and drop it onto a petri dish. After drying, it forms a smooth elastic film with structural color.

[0064] Example 4:

[0065] (1) Add 5g of St and 0.5g of DVB to 100mL of deionized water containing 0.065g of SDS, emulsify at 300rpm for 30min, then raise the reaction temperature to 85℃ and hold for 10min, then add 0.05g of APS to initiate polymerization for 1h to obtain PS seeds with a particle size of approximately 120nm.

[0066] (2) Add 7.5g St and 1g DVB to the reaction system, and then add 0.08g APS to initiate polymerization for 1.5h to obtain PS core with a particle size of about 230nm.

[0067] (3) Add 5g MMA, 15g BA and 0.04g ALMA to the reaction system, and then add 0.1g APS to initiate polymerization for 1.5h to obtain core-shell structure PS@P(MMA-BA) photonic crystal microsphere emulsion with a particle size of about 290nm.

[0068] (4) Take 5 mL of emulsion and drop it onto a petri dish. After drying, it forms a smooth elastic film with structural color.

[0069] Example 5:

[0070] (1) Add 5g of St and 0.5g of DVB to 100mL of deionized water containing 0.065g of SDS, emulsify at 300rpm for 30min, then raise the reaction temperature to 85℃ and hold for 10min, then add 0.05g of APS to initiate polymerization for 1h to obtain PS seeds with a particle size of approximately 120nm.

[0071] (2) Add 7.5g St and 1g DVB to the reaction system, and then add 0.1g APS to initiate polymerization for 1.5h to obtain PS core with a particle size of about 240nm.

[0072] (3) Add 20g EA and 0.04g ALMA to the reaction system, and then add 0.1g APS to initiate polymerization for 1.5h to obtain a core-shell structured PS@PEA photonic crystal microsphere emulsion with a particle size of about 300nm.

[0073] (4) Take 5 mL of emulsion and drop it onto a petri dish. After drying, it forms a smooth elastic film with structural color.

[0074] Example 6:

[0075] (1) Add 5g of AN and 0.5g of DVB to 100mL of deionized water containing 0.065g of SDS, emulsify at 300rpm for 30min, then raise the reaction temperature to 85℃ and hold for 10min, then add 0.05g of APS to initiate polymerization for 1h to obtain PAN seeds with a particle size of approximately 120nm.

[0076] (2) Add 7.5g AN and 1g DVB to the reaction system, and then add 0.05g APS to initiate polymerization for 1.5h to obtain PAN core with a particle size of about 220nm.

[0077] (3) Add 19g EA, 1g BA and 0.04g ALMA to the reaction system, and then add 0.1g APS to initiate polymerization for 1.5h to obtain a core-shell structured PAN@P(EA-BA) photonic crystal microsphere emulsion with a particle size of about 280nm.

[0078] (4) Take 5 mL of emulsion and drop it onto a petri dish. After drying, it forms a smooth elastic film with structural color.

[0079] Example 7:

[0080] (1) Add 5g of MMA and 0.5g of DVB to 100mL of deionized water containing 0.065g of SDS, emulsify at 300rpm for 30min, then raise the reaction temperature to 85℃ and hold for 10min, then add 0.05g of APS to initiate polymerization for 1h to obtain PMMA seeds with a particle size of approximately 120nm.

[0081] (2) Add 7.5g MMA and 1g DVB to the reaction system, and then add 0.20g APS to initiate polymerization for 1.5h to obtain PMMA core with a particle size of about 170nm.

[0082] (3) Add 19g EA, 1g BA and 0.04g ALMA to the reaction system, and then add 0.1g APS to initiate polymerization for 1.5h to obtain a core-shell structured PMMA@P(EA-BA) photonic crystal microsphere emulsion with a particle size of about 250nm.

[0083] (4) Take 5 mL of the emulsion and drop it onto a petri dish. After drying, a smooth, elastic film forms, accompanied by structural colors. Comparative Example 1:

[0084] (1) Add 5g of St and 0.5g of DVB to 100mL of deionized water containing 0.065g of SDS, emulsify at 300rpm for 30min, then raise the reaction temperature to 85℃ and hold for 10min, then add 0.05g of APS to initiate polymerization for 1h to obtain PS seeds with a particle size of approximately 120nm.

[0085] (2) Add 7.5g St and 1g DVB to the reaction system, and then add 0.05g APS to initiate polymerization for 1.5h to obtain PS microspheres with a particle size of about 220nm.

[0086] (3) Take 5 mL of emulsion and drop it onto a petri dish. After drying, structural color appears, but there is a cracking problem.

[0087] Comparative Example 2:

[0088] (1) Add 5g of St and 0.5g of DVB to 100mL of deionized water containing 0.065g of SDS, emulsify at 300rpm for 30min, then raise the reaction temperature to 85℃ and hold for 10min, then add 0.05g of APS to initiate polymerization for 1h to obtain PS seeds with a particle size of approximately 120nm.

[0089] (2) Add 7.5g St and 1g DVB to the reaction system, and then add 0.05g APS to initiate polymerization for 1.5h to obtain PS core with a particle size of about 220nm.

[0090] (3) Add 5g MMA, 15g EA and 0.04g ALMA to the reaction system, and then add 0.1g APS to initiate polymerization for 1.5h to obtain a core-shell structure PS@PEA photonic crystal microsphere emulsion with a particle size of about 300nm.

[0091] (4) Take 5 mL of emulsion and drop it onto a petri dish. After drying, a cracked film will form.

[0092] Comparative Example 3:

[0093] (1) Add 5g of St and 0.5g of DVB to 100mL of deionized water containing 0.065g of SDS, emulsify at 300rpm for 30min, then raise the reaction temperature to 85℃ and hold for 10min, then add 0.05g of APS to initiate polymerization for 1h to obtain PS seeds with a particle size of approximately 120nm.

[0094] (2) Add 7.5gSt and 1gDVB to the reaction system, and then add 0.05gAPS to initiate polymerization for 1.5h to obtain PS core with a particle size of about 220nm.

[0095] (3) Add 20gBA and 0.04gALMA to the reaction system, and then add 0.1gAPS to initiate polymerization for 1.5h to obtain a core-shell structure PS@PBA photonic crystal microsphere emulsion with a particle size of about 320nm.

[0096] (4) Take 5 mL of emulsion and drop it onto a petri dish. After drying, a smooth film is formed without structural color. However, the film has no strength and tends to string when stretched, making it impossible to recover.

[0097] Comparative Example 4:

[0098] (1) Add 12.5g of St and 1.5g of DVB to 100mL of deionized water containing 0.065g of SDS, emulsify at 300rpm for 30min, then raise the reaction temperature to 85℃ and hold for 10min, then add 0.1g of APS to initiate polymerization for 2.5h to obtain the PS core.

[0099] (2) Add 19g EA, 1g BA and 0.04g ALMA to the reaction system, and then add 0.1g APS to initiate polymerization for 1.5h to obtain core-shell structure PS@P(EA-BA) photonic crystal microsphere emulsion.

[0100] (3) Take 5 mL of emulsion and drop it onto a petri dish. After drying, it forms a smooth elastic film, but no structural color appears.

[0101] Table 1. Comparison of results between Examples 1-7 and Comparative Examples 1-4

[0102]

[0103]

[0104] Example 8: Optimization of the combination ratio of monomers used in the soft shell in step (3)

[0105] (1) Add 5g of St and 0.5g of DVB to 100mL of deionized water containing 0.065g of SDS, emulsify at 300rpm for 30min, then raise the reaction temperature to 85℃ and hold for 10min, then add 0.05g of APS to initiate polymerization for 1h to obtain PS seeds with a particle size of about 120nm.

[0106] (2) Add 7.5gSt and 1gDVB to the reaction system, and then add 0.05gAPS to initiate polymerization for 1.5h to obtain PS core with a particle size of about 220nm.

[0107] (3) Add a certain amount of EA, BA and 0.04g ALMA to the reaction system, and then add 0.1g APS to initiate polymerization for 1.5h to obtain a core-shell structure PS@P(EA-BA) photonic crystal microsphere emulsion with a particle size of about 280nm.

[0108] (4) Take 5 mL of emulsion and drop it onto a petri dish. After drying, a smooth film will form. The results are shown in Table 2.

[0109] Table 2

[0110] EA addition amount (g) BA addition amount (g) EA to BA quality ratio Film formation results Structural color 20 0 Example 5 Elastic and smooth without cracks red 19 1 19:1 (Example 1) Elastic and smooth without cracks green 15 5 15：5 Poor elasticity and easily deformed green 10 10 10：10 Inelastic but does not crack green 5 15 5：15 Inelastic but does not crack Unstructured color 1 19 1：19 Inelastic but does not crack Unstructured color 0 20 Comparative Example 3 Inelastic but does not crack Unstructured color

[0111] Example 9: Optimization of the combination ratio of monomers used in the soft shell in step (3)

[0112] (1) Add 5g of St and 0.5g of DVB to 100mL of deionized water containing 0.065g of SDS, emulsify at 300rpm for 30min, then raise the reaction temperature to 85℃ and hold for 10min, then add 0.05g of APS to initiate polymerization for 1h to obtain PS seeds with a particle size of approximately 120nm.

[0113] (2) Add 7.5gSt and 1gDVB to the reaction system, and then add 0.08gAPS to initiate polymerization for 1.5h to obtain PS core with a particle size of about 230nm.

[0114] (3) Add a certain amount of MMA, BA and 0.04g ALMA to the reaction system, and then add 0.1g APS to initiate polymerization for 1.5h to obtain a core-shell structure PS@P(MMA-BA) photonic crystal microsphere emulsion with a particle size of about 290nm.

[0115] (4) Take 5 mL of emulsion and drop it onto a petri dish. After drying, a smooth film will form. The results are shown in Table 3.

[0116] Table 3

[0117] MMA addition amount (g) BA addition amount (g) MMA to BA quality ratio Film formation results Structural color 5 15 1:3 (Example 4) Elastic and smooth without cracks green 8 12 1：1.5 The dura mater is inelastic and does not crack. Unstructured color 10 10 1：1 The dura mater is inelastic and does not crack. Unstructured color 12 8 1.5：1 The dura mater is inelastic and does not crack. Unstructured color 15 5 3：1 The dura mater is inelastic and does not crack. Unstructured color

[0118] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a hard-core soft-shell photonic crystal composite microsphere which can self-form an elastic film, characterized in that, The core-shell structure is gradually formed through seed emulsion polymerization, including the following steps: S1. A portion of the hard core is emulsified with monomer, crosslinking agent, emulsifier, and water, and then an initiator is added to react and obtain a polymer seed emulsion. S2. Add another portion of the hard core monomer, crosslinking agent, and initiator to the obtained polymer seed emulsion, and polymerize to obtain a hard core microsphere system; S3. Add the soft-shell monomer, crosslinking agent, and initiator to the obtained hard-core microsphere system to initiate polymerization and obtain hard-core soft-shell photonic crystal composite microspheres. The hard core monomer is one of styrene, methyl methacrylate, and acrylonitrile; the mass ratio of the hard core monomer in S1 to the hard core monomer in S2 is 1:1-2; The monomer used for the soft shell is selected from: ① A combination of ethyl acrylate and butyl acrylate, wherein the mass ratio of ethyl acrylate to butyl acrylate is 19-20:1, or ②A combination of methyl methacrylate and butyl acrylate, wherein the mass ratio of methyl methacrylate to butyl acrylate is 1:3; In S3, the amount of crosslinking agent relative to the monomer used in the soft shell is 0.2-1.0 wt%; The hard-core soft-shell photonic crystal microspheres in S3 have a particle size of 200-300 nm and a polymer dispersibility index of less than 0.

08.

2. The production method according to claim 1, characterized by, The emulsifier is one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, or sodium dodecyl sulfonate.

3. The preparation method according to claim 1, characterized in that, The crosslinking agent is one or more of divinylbenzene and allyl methacrylate.

4. The preparation method according to claim 1, characterized in that, In S1 or S2, the amount of crosslinking agent relative to the monomer used for hardening the core in this step is 10-14 wt%.

5. The preparation method according to claim 1, characterized in that, The initiator is one or more of ammonium persulfate, potassium persulfate, and sodium persulfate.

6. The preparation method according to claim 1, characterized in that, The polymer seeds in S1 have a particle size of 120 nm and a polymer dispersibility index of less than 0.

08.

7. The preparation method according to claim 1, characterized in that, The hard-core microspheres in S2 have a particle size of 170-220 nm and a polymer dispersibility index of less than 0.

08.

8. Hard-core soft-shell photonic crystal composite microspheres prepared by the preparation method according to any one of claims 1-7.

9. A structurally colored thin film, characterized in that, Contains the hard-core soft-shell photonic crystal composite microspheres as described in claim 8.

10. The application of the hard-core soft-shell photonic crystal composite microspheres according to claim 8 in colored coatings.

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