A High-Saturation Structural Color Photonic Crystal Microsphere, Its Preparation Method and Application

Abstract

This invention discloses a highly saturated structural color photonic crystal microsphere, its preparation method, and its applications, belonging to the field of crystal materials technology. This invention employs a two-step method to prepare a water-in-oil-in-water (W / O / W) multiple emulsion. Through thermal curing of the oil phase, the liquid colloidal crystal is coated to form photonic crystal-cured microspheres, which can be directly applied as photonic crystal pigments without further assembly. The microspheres prepared by this method retain the highly saturated structural color of the photonic crystal and exhibit a certain angle dependence. The preparation process is simple, the microsphere size is adjustable, and the cost is low. This invention can synthesize structural color microspheres of various colors by synthesizing P(St / MAA) nanospheres of different particle sizes, broadening the application of structural colors in cosmetics, coatings, and other fields, achieving vibrant colors, environmental friendliness, and colorfastness.

Description

Technical Field

[0001] This invention relates to a highly saturated structural color photonic crystal microsphere, its preparation method and application, belonging to the field of crystal material technology. Background Technology

[0002] Photonic crystals are periodic array nanostructures composed of two or more media with different refractive indices. The photonic band gap within the structure impedes the propagation of incident light within a certain wavelength range, giving photonic crystals unique structural colors. The structural colors of photonic crystals primarily rely on their periodic arrangement. Compared to pigments, photonic crystal pigments possess characteristics such as permanent colorfastness, high saturation, and angle dependence. However, due to their unique color-generating mechanism, preparing well-dispersed photonic crystal particles is only the first step in synthesizing photonic crystals. They must also be assembled into a photonic crystal structure using bottom-up or top-down methods, such as vertical deposition, evaporation-induced methods, spin-coating, and field-induced methods. However, in practical applications, the self-assembly of photonic crystal particles into a periodic arrangement without external force is challenging.

[0003] Liquid colloidal crystals possess a periodically arranged photonic crystal structure, and photonic crystal particles can be rapidly assembled through solvent evaporation, centrifugation, and other methods. These methods can increase the number of photonic crystal particles in the colloidal system and reduce the spacing between nanoparticles. When the spacing is reduced to a certain extent, the electrostatic repulsion and van der Waals forces between particles reach equilibrium, allowing the particles to form a stable, ordered arrangement, thereby producing structural color. However, the prepared liquid colloidal crystals are affected by incoherent scattered light, resulting in a reduction in the saturation of the structural color. Existing technology CN110054933A controls the saturation of liquid photonic crystal pigment colors by adding light absorbers and uses binders to increase the stability of the photonic crystal structure and the durability of the structural color. The prepared liquid photonic crystal structural color pigment ink requires external forces such as smearing and spraying to complete the assembly of the photonic crystals during use, limiting its application scenarios. Furthermore, the light absorber and photonic crystal microspheres are doped by physical forces, resulting in weak bonding. The light absorber is prone to precipitation from the photonic crystal pigment ink, causing problems such as uneven color.

[0004] Existing droplet fabrication often employs microfluidic technology. Within precisely designed micron-sized channels, the convective flow of two or more immiscible liquids is controlled by a microfluidic chip, forming well-dispersed microdroplets with controllable morphology under shear or extrusion forces. The fabrication of structured color microspheres using microfluidic technology relies on precise microchannel structures; the capillary diameter within the channel determines the size of the structured color microspheres, and different sizes require equipment changes. Therefore, this technology is costly and requires a high level of expertise, limiting large-scale production. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing highly saturated structural color photonic crystal microspheres. By preparing photonic crystal-cured microspheres, no further assembly is required, and they can be used directly as photonic crystal pigments.

[0006] This invention is achieved through the following technical solution:

[0007] The first objective of this invention is to provide a method for preparing highly saturated structural color photonic crystal microspheres, comprising the following steps:

[0008] S1. Poly(styrene-methacrylic acid) nanospheres were prepared by initiating polymerization of styrene and methacrylic acid.

[0009] S2. Poly(styrene-methacrylic acid) nanospheres were prepared into a dispersion, and the dispersion was mixed with dopamine hydrochloride and stirred to carry out a polymerization reaction to obtain polydopamine-modified poly(styrene-methacrylic acid) nanospheres.

[0010] S3. Polydopamine-modified poly(styrene-methacrylic acid) nanospheres were prepared into a dispersion as an aqueous phase and added to the oil phase for homogenization to obtain a water-in-oil emulsion. After standing, the upper oil phase was removed, and PDMS prepolymer and initiator were added to the remaining oil phase and mixed to obtain a curable water-in-oil emulsion.

[0011] S4. Slowly add the curable oil-in-water emulsion prepared in step S3 into the xanthan gum solution, stir to obtain a water-in-oil-in-water emulsion, and cure to obtain the high-saturation structural color photonic crystal microspheres.

[0012] In one embodiment of the present invention, in step S1, polymerization is initiated by using one or more of ammonium sulfate (APS) and potassium persulfate (KPS) as initiators.

[0013] In one embodiment of the present invention, in step S2, the mass fraction of poly(styrene-methacrylic acid) nanospheres in the dispersion is 10-40%.

[0014] In one embodiment of the present invention, the amount of dopamine hydrochloride added is 10 to 50% of the mass of poly(styrene-methacrylic acid) nanospheres, by mass fraction.

[0015] In one embodiment of the present invention, the mass fraction of polydopamine-modified poly(styrene-methacrylic acid) nanospheres in the dispersion of polydopamine-modified poly(styrene-methacrylic acid) nanospheres is 20-40%.

[0016] In one embodiment of the present invention, in step S3, the mass ratio of the aqueous phase to the oil phase is 1:2 to 9.

[0017] In one embodiment of the present invention, in step S3, the oil phase is composed of grease with 0.1 to 1% surfactant added, by mass fraction.

[0018] In one embodiment of the present invention, the surfactant is lauryl alcohol / PEG-9 / polydimethylsiloxane / polydimethylsiloxane, namely KF-6038.

[0019] In one embodiment of the present invention, the oil is one or more of ethylhexyl palmitate, caprylic / capric triglyceride, and isopropyl myristate.

[0020] In one embodiment of the present invention, in step S3, homogenization is performed at a rotational speed of 2000-4000 rpm for 10-15 seconds.

[0021] In one embodiment of the present invention, the ratio of residual oil phase:PDMS prepolymer:initiator by mass is 2-3:8-10:1.

[0022] In one embodiment of the present invention, the xanthan gum solution has a mass fraction of 0.5% to 2%.

[0023] In one embodiment of the present invention, the mass ratio of the curable water-in-oil emulsion to the xanthan gum solution is 1:15 to 50.

[0024] In one embodiment of the present invention, in step S4, the stirring is performed by magnetic stirring at a speed of 300-500 rpm for 2-5 hours.

[0025] In one embodiment of the present invention, in step S4, curing is performed by placing the emulsion in a water bath at 60-65°C for 6-12 hours for heat curing.

[0026] A second objective of this invention is to provide highly saturated structural color photonic crystal microspheres prepared by the method described above.

[0027] A third objective of this invention is to provide the application of the aforementioned highly saturated structural color photonic crystal microspheres in cosmetics and coatings.

[0028] The beneficial effects of this invention are:

[0029] This invention employs a two-step method to prepare a water-in-oil (W / O / W) multiple emulsion. The liquid colloidal crystal is then coated with the emulsion via thermal curing of the oil phase, forming photonic crystal-cured microspheres. These microspheres can be directly applied as photonic crystal pigments without further assembly. The microspheres prepared by this method retain the highly saturated structural colors of photonic crystals and exhibit a certain degree of angle dependence. The preparation process is simple, the microsphere size is adjustable, and the cost is low.

[0030] This invention can synthesize P(St / MAA) nanospheres of different sizes to prepare structural color microspheres of various colors, thus broadening the application of structural colors in cosmetics, coatings and other fields, and achieving the effect of bright colors, green environmental protection and never fading. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 P(St / MAA) liquid colloidal crystals (20wt%) and P(St / MAA)@PDA liquid colloidal crystals (20wt%) with different dopamine additions (10%, 20%, 30%, 40%, 50%);

[0033] Figure 2 P(St / MAA)@PDA liquid colloidal crystals with different mass fractions of P(St / MAA)@PDA nanoparticles (10%, 20%, 30%, 40%);

[0034] Figure 3 Images of P(St / MAA)@PDA structured color microspheres with P(St / MAA)@PDA nanoparticle mass fractions of 20%, 30%, and 40% at different incident angles;

[0035] Figure 4 Hyperdepth images of P(St / MAA)@PDA water-in-oil emulsion (a) and P(St / MAA)@PDA structured color microspheres (b) with different emulsifier dosages (0.1%, 0.5%, 1%).

[0036] Figure 5 Images of P(St / MAA)@PDA structured color microspheres with KF-6038 dosages of 0.1%, 0.5%, and 1% at different incident angles.

[0037] Figure 6 Images of blue, green, and red cured microspheres prepared with P(St / MAA) nanoparticles of different sizes (170, 210, 240 nm) at different incident angles. Detailed Implementation

[0038] The present invention will be further illustrated below with specific examples. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0039] Reagents and Materials

[0040] Styrene (St, 99.5%), methacrylic acid (MAA, 98%), ammonium persulfate (APS, 98%), xanthan gum, tris(hydroxymethyl)aminomethane (Tris), and concentrated hydrochloric acid (HCl) were purchased from Sinopharm Chemical Reagent Co., Ltd.; dopamine hydrochloride (DA, 99%+) was purchased from Shanghai Titan Technology Co., Ltd.; PDMS prepolymer and initiator were purchased from Dow Corning Incorporated, Inc.; ethylhexyl palmitate (2-EHP, 99%) was purchased from Shandong Yousuo Chemical Technology Co., Ltd.; KF-6038 was purchased from Shanghai Shin-Etsu Silicon International Trading Co., Ltd.; and ultrapure water with a conductivity of 2.99 μS / cm was provided by Jiangnan University.

[0041] The technical solution of the present invention will be described in detail below with reference to specific embodiments. In the following embodiments, unless otherwise specified, the reagents, materials and equipment used can be purchased commercially, prepared by conventional methods, or commonly used in the industry.

[0042] Example 1:

[0043] Preparation of P(St / MAA) nanospheres: Poly(styrene-methacrylic acid) (P(St / MAA)) nanospheres with a particle size of 210 nm were prepared by soap-free emulsion polymerization. The 210 nm P(St / MAA) nanospheres were then centrifuged to form liquid colloidal crystals, with a P(St / MAA) nanosphere mass fraction of 20% (20 wt%) in the liquid colloidal crystals, which were used for the preparation of P(St / MAA)@PDA microspheres. Different particle sizes of P(St / MAA) nanospheres could be synthesized by changing the amount of styrene added during the polymerization process, resulting in photonic crystals of different colors.

[0044] Preparation of P(St / MAA)@PDA microspheres: A 10 mM Tris-HCl buffer solution was prepared, and the pH was adjusted to 8.5. 20% (w / w) of P(St / MAA) dispersion and dopamine hydrochloride powder were added to this alkaline buffer solution, and the mixture was stirred in the dark for 12 h to obtain P(St / MAA)@PDA microspheres. In this preparation step, the amount of dopamine added was 20% of the mass of the P(St / MAA) nanospheres. The particle size of P(St / MAA)@PDA can be controlled by changing the amount of dopamine hydrochloride added, thus synthesizing nanospheres of different sizes.

[0045] Preparation of W / O emulsion: By mass fraction, 1% of surfactant KF-6038 and 79% ethylhexyl palmitate were stirred and mixed to form an oil phase. 20% of P(St / MAA)@PDA dispersion was added as an aqueous phase. The mixture was homogenized at 3000 rpm for 12 seconds to prepare a water-in-oil (W / O) emulsion. After standing, the upper oil phase was removed. PDMS prepolymer and initiator were added in proportion (remaining oil phase: PDMS prepolymer: initiator = 2.75:10:1) and stirred until uniform to obtain a curable W / O emulsion.

[0046] Preparation of W / O / W cured microspheres: 1 g of W / O emulsion was slowly added to 20 g of xanthan gum solution (mass fraction 1 wt%), and the mixture was magnetically stirred at 400 rpm for 3 h to obtain a W / O / W emulsion. The obtained emulsion was then thermo-cured in a 65℃ water bath for 12 h to cure the PDMS prepolymer, resulting in W / O / W photonic crystal microspheres, which were stored in xanthan gum.

[0047] Example 2: Effect of dopamine addition on the color of P(St / MAA)@PDA liquid crystals

[0048] Liquid colloidal crystals were prepared from 210 nm P(St / MAA) nanospheres by centrifugation, with the P(St / MAA) nanospheres comprising 20% ​​(20 wt%) of the liquid colloidal crystals. Figure 1 As shown, P(St / MAA) liquid colloidal crystals have a certain angle-dependent structural color, but due to the influence of incoherent scattered light, the colloid appears milky white overall, and the saturation of the structural color is not high.

[0049] P(St / MAA)@PDA nanoparticles were prepared by in-situ polymerization of the matting material polydopamine onto the surface of P(St / MAA) nanospheres with a particle size of 210 nm. The amount of dopamine added was 10%–50% of the mass of the P(St / MAA) nanospheres. This was compared with liquid colloidal P(St / MAA) samples. Figure 1The P(St / MAA)@PDA liquid colloidal crystals exhibited brighter colors and suppressed whitening. At dopamine concentrations of 10% and 20%, the liquid colloidal crystals displayed the most vibrant colors with a clear angle dependence. However, at 30%, the angle-dependent structural color disappeared, resulting in a single color. As the dopamine concentration increased from 10% to 50%, the color of the P(St / MAA)@PDA liquid colloidal crystals underwent a redshift, and the brightness continuously decreased, while the angle dependence gradually disappeared. The dopamine coating on the outer layer of the P(St / MAA) nanospheres affected the nanosphere particle size; the increasing particle size caused a redshift in the reflected light from the liquid colloidal crystals. After examining the color performance of the liquid colloidal crystals with different dopamine concentrations, the optimal dopamine concentration was determined to be 10%–20%.

[0050] Example 3: Effect of P(St / MAA)@PDA nanosphere mass fraction on the color of liquid colloidal crystals

[0051] The crystallization behavior of colloids is highly correlated with the mass fraction of photonic crystal particles in liquid colloidal crystal dispersions. As the number of photonic crystal particles per unit mass of dispersion increases, the particle arrangement gradually changes from disordered to periodic, transitioning from an amorphous to a crystalline state, resulting in photonic crystal liquid colloidal crystals. P(St / MAA)@PDA dispersions can be concentrated using centrifugation-ultrasonic dispersion to obtain liquid colloidal crystals with different mass fractions; the mass fraction of P(St / MAA)@PDA nanoparticles in the liquid colloidal crystal dispersions ranges from 10% to 40%.

[0052] like Figure 2 As shown: When the mass fraction of P(St / MAA)@PDA nanoparticles is 10%, the P(St / MAA)@PDA dispersion appears grayish-pink with low color saturation. When the mass fraction reaches 20%, the color saturation and brightness of the liquid colloidal crystals are improved, and the structural color exhibits angle dependence. Increasing the mass fraction from 20% to 30% results in a rapid increase in the color saturation and brightness of the liquid colloidal crystals, with the structural color transitioning from green to red. Besides the effects on structural color saturation, brightness, and angle dependence, the mass fraction of nanoparticles in the liquid colloidal crystals also influences the hue. As the mass fraction gradually increases from 20% to 40%, the color of the P(St / MAA)@PDA liquid colloidal crystals continuously shifts towards blue, and the angle dependence of the structural color eventually spans from blue-green to yellow, orange, and red. After comparing the colors of the liquid colloidal crystals with different particle mass fractions, the optimal condition for the mass fraction of P(St / MAA)@PDA nanoparticles was determined to be 20%–40%.

[0053] Example 4: Effect of P(St / MAA)@PDA nanosphere mass fraction on the color of cured photonic crystal microspheres

[0054] The liquid colloidal crystals (20wt%, 30wt%, and 40wt%) with bright structural colors selected in Example 3 were used to prepare cured photonic crystal microspheres in a W / O / W multiple emulsion format. Figure 3 As shown, when the incident angle increases from 0° to 90°, the color of microspheres with a mass fraction of 20% changes from red to yellowish-green; the color of microspheres with a mass fraction of 30% changes from yellowish-green to bluish-green; and the color of microspheres with a mass fraction of 40% changes from green to bluish-green. Combining sample images from different incident angles, P(St / MAA)@PDA nanoparticles with a mass fraction of 30%–40% exhibit the best color saturation and brightness.

[0055] Example 5: Effect of W / O Emulsion Emulsifier Dosage

[0056] KF-6038, as an emulsifier for water-in-oil emulsions, helps reduce interfacial tension, form stable droplets, and enable the droplets to form an electric double layer, thereby maintaining the dispersion and stability of the emulsion. Figure 4 Figure 'a' shows the effect of different mass fractions of KF-6038 on the particle size and stability of the water-in-oil emulsion. As can be seen from the figure, the particle size of the water-in-oil emulsion is in the micrometer range. When the mass fraction of KF-6038 is 0.1%, the emulsion particle size is relatively large, and droplet breakage leads to colloidal leakage of the photonic crystal. As the mass fraction of KF-6038 increases, the particle size of the W / O emulsion continuously decreases. When the mass fraction of KF-6038 is 1%, the average particle size is 16 μm, and the emulsion maintains good stability without demulsification.

[0057] The mass fraction of KF-6038 not only affects the stability of water-in-oil emulsions, but also reduces the particle size of multi-emulsions as the amount of KF-6038 added increases. Figure 4 (b) In addition, the mass fraction of KF-6038 also has a certain influence on the color of the cured microspheres. For example... Figure 5 As shown, increasing the emulsifier mass fraction from 0.1% to 1% caused the color of the P(St / MAA)@PDA cured microspheres to change from yellow to green. However, the mass fraction of KF-6038 did not affect the angle dependence of the microspheres; the P(St / MAA)@PDA cured microspheres still exhibited a yellow-green-blue-green structural color as the incident light angle changed. Based on the color performance of actual samples, the optimal addition amount of KF-6038 was finally determined to be 0.5%–1%.

[0058] Example 6: Preparation of photonic crystal microspheres of different colors

[0059] The structural color of photonic crystals can be controlled by altering the refractive index, arrangement, and particle size of the building blocks. By controlling the synthesis conditions of P(St / MAA) nanospheres, a series of photonic crystal materials in the visible light range can be obtained. Blue and red photonic crystal-cured microspheres were prepared using P(St / MAA) nanospheres with particle sizes of 170 nm and 240 nm, enriching the color range of photonic crystal microspheres. The structural color microspheres with different particle sizes all exhibited good color saturation and a certain degree of angle dependence. Figure 6 The color of the structured color microspheres with a particle size of 170 nm shifts towards the ultraviolet region as the incident angle increases, exhibiting an angle dependence from purple to blue, while the color of the microspheres with a particle size of 240 nm varies in the range of red to purplish-red.

[0060] Comparative Example 1:

[0061] A 1% xanthan gum solution is used as the external aqueous phase in a multiple emulsion. The xanthan gum effectively improves the interfacial arrangement of the emulsifier and enhances the emulsion's stability. If xanthan gum is not added to the external aqueous phase, and only the emulsifier is used to prepare the multiple emulsion, it is prone to demulsification. The intermediate oil phase, consisting of PDMS prepolymer and initiator, requires a 65°C water bath for 12 hours to achieve complete curing. Without xanthan gum, the multiple emulsion exhibits coalescence and demulsification of water-in-oil droplets under temperature influence, leading to cross-linking between structural color microspheres, irregular microsphere structure, and even affecting the leakage of photonic crystal colloidal crystals in the water-in-oil droplets, resulting in a loss of bright color.

[0062] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing highly saturated structural color photonic crystal microspheres, characterized in that, Includes the following steps: S1. Poly(styrene-methacrylic acid) nanospheres were prepared by initiating polymerization of styrene and methacrylic acid. S2. Poly(styrene-methacrylic acid) nanospheres were prepared into a dispersion, and the dispersion was mixed with dopamine hydrochloride and stirred to carry out a polymerization reaction to obtain polydopamine-modified poly(styrene-methacrylic acid) nanospheres. S3. Polydopamine-modified poly(styrene-methacrylic acid) nanospheres were prepared into a dispersion as an aqueous phase and added to the oil phase for homogenization to obtain a water-in-oil emulsion. After standing, the upper oil phase was removed, and PDMS prepolymer and initiator were added to the remaining oil phase and mixed to obtain a curable water-in-oil emulsion. S4. Slowly add the curable oil-in-water emulsion prepared in step S3 into the xanthan gum solution, stir to obtain a water-in-oil-in-water emulsion, and cure to obtain the high-saturation structural color photonic crystal microspheres.

2. The preparation method according to claim 1, characterized in that, The amount of dopamine hydrochloride added is 10 to 50% of the mass of poly(styrene-methacrylic acid) nanospheres, by mass fraction.

3. The preparation method according to claim 1, characterized in that, In the dispersion of polydopamine-modified poly(styrene-methacrylic acid) nanospheres, the mass fraction of polydopamine-modified poly(styrene-methacrylic acid) nanospheres is 20-40%.

4. The preparation method according to claim 1, characterized in that, In step S3, the mass ratio of the aqueous phase to the oil phase is 1:2 to 9.

5. The preparation method according to claim 1, characterized in that, In step S3, the oil phase, by mass fraction, consists of grease with 0.1-1% surfactant added.

6. The preparation method according to claim 5, characterized in that, The surfactant is lauryl alcohol / PEG-9 / polydimethylsiloxane / polydimethylsiloxane, and the oil is one or more of ethylhexyl palmitate, caprylic / capric triglyceride, and isopropyl myristate.

7. The preparation method according to claim 1, characterized in that, By mass ratio, the ratio of remaining oil phase:PDMS prepolymer:initiator is 2-3:8-10:

1.

8. The preparation method according to claim 1, characterized in that, The xanthan gum solution has a mass fraction of 0.5-2%; the mass ratio of the curable water-in-oil emulsion to the xanthan gum solution is 1:15-50.

9. A highly saturated structural color photonic crystal microsphere prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the high-saturation structural color photonic crystal microspheres according to claim 9 in cosmetics and coatings.

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