High-saturation structural color photonic crystal microsphere as well as preparation method and application thereof

Abstract

The invention discloses a high-saturation structural color photonic crystal microsphere as well as a preparation method and application thereof, and belongs to the technical field of crystal materials. A two-step method is adopted for preparing water-in-oil-in-water (W / O / W) multiple emulsion, liquid colloidal crystals are coated through oil-phase thermocuring to form the photonic crystal cured microspheres, and the photonic crystal cured microspheres can be directly applied as photonic crystal pigment and do not need to be assembled again. The microspheres prepared by the method provided by the invention reserve the high-saturation structural color of the photonic crystal, and have certain angle dependence, the preparation process is simple and convenient, the size of the microspheres is adjustable, and the cost is lower. According to the method, the structural color microspheres with various colors can be prepared by synthesizing the P (St / MAA) nanospheres with different particle sizes, the application range of the structural colors in the fields of cosmetics, coatings and the like is widened, and the effects of being gorgeous in color, green, environmentally friendly and free of color fading are achieved.

Description

Technical Field

[0001] The present invention relates to a high-saturation structural color photonic crystal microsphere, a preparation method thereof and an application thereof, belonging to the technical field of crystal materials. Background Art

[0002] A photonic crystal is a periodic array nanostructured material composed of two or more different refractive index media. The photonic band gap in the structure hinders the propagation of incident light within a certain wavelength range, enabling the photonic crystal to have a unique structural color. The structural color of the photonic crystal is mainly dependent on its periodically arranged structure. Compared with pigment dyes, the photonic crystal pigment has the characteristics of never fading, high saturation, and angle dependence. However, due to its special color generation mechanism, preparing photonic crystal particles with good monodispersity is only the first step in synthesizing photonic crystals. It is also necessary to assemble them into a photonic crystal structure through bottom-up or top-down methods, such as vertical deposition method, evaporation-induced method, spin coating method, field force induction method, etc. However, in the actual application process, due to the lack of external force, it is challenging for photonic crystal particles to self-assemble into a periodic arrangement.

[0003] Liquid colloidal crystals have a periodically arranged photonic crystal structure, and rapid assembly of photonic crystal particles can be achieved through methods such as solvent evaporation and centrifugation. 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 the particles reach equilibrium, enabling the particles to form a stable ordered arrangement, thereby generating a structural color. However, the prepared liquid colloidal crystal is affected by incoherent scattered light, and the saturation of the presented structural color is reduced. In the prior art CN110054933A, an absorbent is added to regulate the saturation of the color of the liquid photonic crystal pigment, and an adhesive is added 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 needs to complete the assembly of the photonic crystal through external forces such as smearing and spraying during use, and the application scenario is limited; moreover, the absorbent and the photonic crystal microspheres are doped through physical forces, and the binding force is weak, and the absorbent is prone to precipitate from the photonic crystal pigment ink, resulting in problems such as uneven color.

[0004] In the existing processing of droplets, microfluidic technology is often used for processing. In precisely designed micron-scale channels, the convective flow of two or more immiscible liquids controlled by a microfluidic chip forms monodisperse and morphologically controllable microdroplets under the action of shear force or extrusion force. The preparation of structural color microspheres by microfluidic technology depends on the precise microchannel structure, and the capillary diameter in the channel determines the size of the structural color microspheres. To produce microspheres of different sizes, the equipment needs to be replaced. Therefore, the cost of this technology and the professional requirements for operation are relatively high, and large-scale production is restricted. Summary of the Invention

[0005] To solve the deficiencies of the prior art, the present invention provides a method for preparing high-saturation structural color photonic crystal microspheres. By preparing the photonic crystal solidified microspheres, there is no need for further assembly, and they can be directly used as photonic crystal pigments.

[0006] The present invention is achieved through the following technical solutions:

[0007] The first object of the present invention is to provide a method for preparing high-saturation structural color photonic crystal microspheres, comprising the following steps:

[0008] S1. Polymerize styrene and methacrylic acid to prepare poly(styrene-methacrylic acid) nanospheres;

[0009] S2. Prepare a dispersion of poly(styrene-methacrylic acid) nanospheres, mix the dispersion with dopamine hydrochloride, and stir to carry out a polymerization reaction to obtain poly(styrene-methacrylic acid) nanospheres modified with polydopamine;

[0010] S3. Prepare a dispersion of poly(styrene-methacrylic acid) nanospheres modified with polydopamine as the aqueous phase, add it to the oil phase for homogenization treatment to obtain a water-in-oil emulsion, remove the upper oil phase after standing, and add a PDMS prepolymer and an initiator to the remaining oil phase and mix evenly to obtain a curable water-in-oil emulsion;

[0011] S4. Slowly add the curable water-in-oil emulsion prepared in step S3 to 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, the polymerization is initiated by one or more of ammonium persulfate (APS) and potassium persulfate (KPS) as initiators.

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

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

[0015] In one embodiment of the present invention, in the dispersion of poly(styrene-methacrylic acid) nanospheres modified with polydopamine, the mass fraction of poly(styrene-methacrylic acid) nanospheres modified with polydopamine 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 1:2-9.

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

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

[0019] In one embodiment of the present invention, the grease is one or more of ethylhexyl palmitate, triglyceride caprylate / caprate, and isopropyl myristate.

[0020] In one embodiment of the present invention, in step S3, the homogenization is carried out at a rotation speed of 2000-4000 rpm for 10-15 s.

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

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

[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: 15-50.

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

[0025] In one embodiment of the present invention, in step S4, the curing is to thermally cure the emulsion in a water bath at 60-65 °C for 6-12 h.

[0026] The second object of the present invention is to provide highly saturated structural color photonic crystal microspheres prepared by the above method.

[0027] The third object of the present invention is to provide the application of the highly saturated structural color photonic crystal microspheres in cosmetics and coatings.

[0028] The beneficial effects of the present invention:

[0029] The present invention uses a two-step method to prepare water-in-oil-in-water (W / O / W) multiple emulsions. Through the 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 the method of the present invention retain the highly saturated structural color of the photonic crystal, and have a certain angular dependence. The preparation process is simple, the microsphere size can be adjusted, and the cost is low.

[0030] The present invention can prepare structural color microspheres of various colors by synthesizing P (St / MAA) nanospheres with different particle sizes, broaden the application of structural colors in the fields of cosmetics, coatings, etc., and achieve the effects of brilliant colors, green environmental protection, and never fading. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

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

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

[0034] Figure 3 Sample images of P(St / MAA)@PDA structural color microspheres at different incident angles with a mass fraction of 20%, 30%, and 40% of P(St / MAA)@PDA nanoparticles;

[0035] Figure 4 Super depth of field images of P(St / MAA)@PDA oil-in-water emulsion (a) and P(St / MAA)@PDA structural color microspheres (b) at different emulsifier dosages (0.1%, 0.5%, 1%);

[0036] Figure 5 The sample pictures of P(St / MAA)@PDA structural color microspheres with different incident angles and KF-6038 dosage of 0.1%, 0.5%, and 1%;

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

[0038] The present invention will be further described below in conjunction with specific examples. These examples are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0039] Reagents and Materials

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

[0041] The technical solution of the present invention will be described in detail below in conjunction with specific examples. In the following examples, unless otherwise specified, the reagents, materials and equipment used can be obtained from commercial sources, or prepared by conventional methods, or commonly used in this 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 P(St / MAA) nanospheres with a particle size of 210 nm were prepared into a liquid colloidal crystal by centrifugation. The mass fraction of P(St / MAA) nanospheres in the liquid colloidal crystal was 20% (20 wt%), which was used for the preparation of P(St / MAA)@PDA microspheres. During the polymerization process, P(St / MAA) nanospheres with different particle sizes can be synthesized by changing the amount of styrene added, and photonic crystals of different colors can be obtained.

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

[0045] Preparation of W / O emulsion: By mass fraction, 1% surfactant KF-6038 and 79% ethylhexyl palmitate were stirred and mixed to form the oil phase, and 20% P(St / MAA)@PDA dispersion was added as the water phase. A water-in-oil (W / O) emulsion was prepared by homogenizing at a speed of 3000 rpm for 12 s using a homogenizer. After standing, the upper oil phase was removed, and PDMS prepolymer and initiator were added according to the ratio (remaining oil phase: PDMS prepolymer: initiator = 2.75:10:1), and stirred and mixed evenly 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 magnetically stirred at a speed of 400 rpm for 3 h to obtain a W / O / W emulsion. The obtained emulsion was thermally cured in a water bath at 65 °C for 12 h to cure the PDMS prepolymer, obtaining W / O / W photonic crystal microspheres, which were stored in xanthan gum.

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

[0048] P(St / MAA) nanospheres with a particle size of 210 nm were prepared into liquid colloidal crystals by centrifugation, and the mass fraction of P(St / MAA) nanospheres in the liquid colloidal crystals was 20% (20 wt%). As Figure 1 shown, P(St / MAA) liquid colloidal crystals have an angle-dependent structural color, but affected by incoherent scattered light, the colloid as a whole appears milky white, and the structural color saturation is not high.

[0049] Polydopamine, an extinction material, was in-situ polymerized on the surface of P(St / MAA) nanospheres with a particle size of 210 nm to prepare P(St / MAA)@PDA nanoparticles, and the addition amount of dopamine was 10% - 50% of the mass of P(St / MAA) nanospheres. Comparing with the liquid colloidal crystal P(St / MAA) sample ( Figure 1) The color of the P(St / MAA)@PDA liquid colloidal crystal is brighter, and the whitening phenomenon is suppressed. When the dopamine addition amount is 10% and 20%, the color of the liquid colloidal crystal is the brightest and has an obvious angular dependence. When the addition amount is increased to 30%, the structural color with angular dependence is lost, presenting a single color. As the dopamine addition amount increases from 10% to 50%, the color of the P(St / MAA)@PDA liquid colloidal crystal undergoes a red shift, and the brightness continuously decreases, and the angular dependence gradually disappears. The coating of dopamine on the outer layer of P(St / MAA) nanospheres affects the particle size of the nanospheres. The continuously increasing particle size causes the reflected light of the liquid colloidal crystal to have a red shift. After investigating the color performance of the liquid colloidal crystals with different dopamine addition amounts, the optimal condition for the dopamine addition amount is finally determined to be 10% - 20%.

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

[0051] The crystallization behavior of the colloid is highly correlated with the mass fraction of the photonic crystal particles in the liquid colloidal crystal dispersion. As the number of photonic crystal particles present in the unit mass dispersion continuously increases, the arrangement of the particles will gradually change from disordered to periodic arrangement, transforming from an amorphous state to a crystalline state, generating a photonic crystal liquid colloidal crystal. The P(St / MAA)@PDA dispersion can be concentrated by 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 dispersion is 10% - 40%.

[0052] As Figure 2 shown: When the mass fraction of P(St / MAA)@PDA nanoparticles is 10%, the P(St / MAA)@PDA dispersion presents a gray-pink color with low color saturation. When the mass fraction reaches 20%, the color saturation and brightness of the liquid colloidal crystal are both improved, and the structural color shows angular dependence. When the mass fraction increases from 20% to 30%, the color saturation and brightness of the liquid colloidal crystal increase rapidly, and the structural color shows a leap from green to red. In addition to the effects on the structural color saturation, brightness, and angular dependence, the mass fraction of the nanoparticles in the liquid colloidal crystal also affects the hue. As the mass fraction gradually increases from 20% to 40%, the color of the P(St / MAA)@PDA liquid colloidal crystal continuously undergoes a blue shift, and the angular dependence of the structural color finally reaches a span range 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 is finally determined to be 20% - 40%.

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

[0054] The liquid colloidal crystals (20 wt%, 30 wt%, 40 wt%) with bright structural colors screened in Example 3 were prepared into solidified photonic crystal microspheres in the form of W / O / W multiple emulsions. As Figure 3 shown, when the incident angle increased from 0° to 90°, the color of the microspheres with a mass fraction of 20% changed from red to yellow-green; the color of the microspheres with a mass fraction of 30% changed from yellow-green to blue-green; the color of the microspheres with a mass fraction of 40% changed from green to blue-green. Combining the sample diagrams at different incident angles, the saturation and brightness of the colors of P(St / MAA)@PDA microspheres with a P(St / MAA)@PDA nanoparticle mass fraction of 30% - 40% showed the best performance.

[0055] Example 5: Influence of the dosage of the W / O emulsion emulsifier

[0056] KF-6038, as the emulsifier of the water-in-oil emulsion, helps to reduce the interfacial tension, form stable droplets, and enable the droplets to form a double electric layer, thereby maintaining the dispersion and stability of the emulsion. Figure 4 In a, the influence of different mass fractions of KF-6038 on the particle size and stability of the water-in-oil emulsion is shown. It can be seen from the figure that the particle sizes of the water-in-oil emulsions are all in the micron level. When the mass fraction of KF-6038 is 0.1%, the emulsion particle size is relatively large, and there is leakage of the photonic crystal colloidal crystal due to droplet rupture; 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 can maintain good stability without demulsification.

[0057] The mass fraction of KF-6038 not only affects the stability of the water-in-oil emulsion, but also the particle size of the multiple emulsion decreases with the increase of the addition amount of KF-6038 ( Figure 4 in b). In addition, the mass fraction of KF-6038 also has a certain influence on the color of the solidified microspheres. As Figure 5 shown, when the mass fraction of the emulsifier increases from 0.1% to 1%, the color of the P(St / MAA)@PDA solidified microspheres changes from yellow to green. However, the mass fraction of KF-6038 does not affect the angle dependence of the microspheres. As the incident light angle changes, the P(St / MAA)@PDA solidified microspheres still exhibit the structural colors of yellow - green - blue-green. Combining the color performance of the actual samples, the optimal addition amount of KF-6038 is finally determined to be 0.5% - 1%.

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

[0059] The structural color of photonic crystals can be regulated by changing the refractive index, arrangement, particle size, etc. of the building units of photonic crystals. By regulating the synthesis conditions of P(St / MAA) nanospheres, a series of photonic crystal materials with colors in the visible light range can be obtained. P(St / MAA) nanospheres with particle sizes of 170 nm and 240 nm were selected to prepare blue and red photonic crystal cured microspheres, enriching the color types of photonic crystal microspheres. The structural color microspheres with different particle sizes all have good color saturation and a certain angular dependence( Figure 6 ). For the structural color microspheres with a P(St / MAA) particle size of 170 nm, as the incident angle increases, the color shifts towards the ultraviolet region, showing a purple-blue angular dependence. While for the microspheres with a P(St / MAA) particle size of 240 nm, the color changes within the range of red-magenta.

[0060] Comparative Example 1:

[0061] A 1% xanthan gum solution was used as the outer aqueous phase of the multiple emulsion. The xanthan gum therein can effectively improve the arrangement of the emulsifier at the interface and enhance the stability of the emulsion. If xanthan gum is not added to the outer aqueous phase and only the emulsifier is used to prepare the multiple emulsion, the multiple emulsion is prone to demulsification. The PDMS prepolymer and initiator in the middle oil phase need to be heated in a water bath at 65 °C for 12 h to complete full curing. Under the influence of temperature, the water-in-oil-in-water droplets of the multiple emulsion without xanthan gum undergo coalescence and demulsification, resulting in cross-linking between the structural color microspheres, the irregular microsphere structure, and even affecting the leakage of the photonic crystal colloidal crystal in the oil-in-water droplets and losing the bright color.

[0062] The embodiments provided above are not intended to limit the scope covered by the present invention, nor are the described steps intended to limit their execution order. Obvious improvements made by those skilled in the art to the present invention in combination with the existing common general knowledge also fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing highly saturated structural color photonic crystal microspheres, characterized in that: The steps include: S1, initiating polymerization of styrene and methacrylic acid to prepare poly(styrene-methacrylic acid) nanoparticles; S2, preparing poly(styrene-methacrylic acid) nanoparticles into a dispersion, mixing the dispersion with dopamine hydrochloride and stirring to perform a polymerization reaction, thereby obtaining polydopamine-modified poly(styrene-methacrylic acid) nanoparticles; S3, preparing a dispersion of polydopamine-modified poly(styrene-methacrylic acid) nanospheres as a water phase, adding the dispersion to an oil phase for homogenization to obtain a water-in-oil emulsion, removing the upper oil phase after standing, adding a PDMS prepolymer and an initiator to the remaining oil phase and mixing to obtain a curable water-in-oil emulsion; S4, slowly adding the curable water-in-oil emulsion prepared in step S3 into the xanthan gum solution, stirring to obtain a water-in-oil-in-water emulsion, and curing to obtain the highly saturated structural color photonic crystal microspheres.

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

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

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

5. The preparation method according to claim 1, characterized in that: In step S3, the composition of the oil phase is oil to which 0.1 to 1% of surfactant is added, calculated by mass fraction.

6. The preparation method according to claim 5, characterized in that: The surfactant is lauryl alcohol / PEG-9 / polydimethylsiloxyethyl / 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 remaining oil phase: PDMS prepolymer: initiator = 2-3: 8-10:

1.

8. The preparation method according to claim 1, characterized in that: The mass fraction of the xanthan gum solution is 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. Use of the highly saturated structural color photonic crystal microspheres according to claim 9 in cosmetics and coatings.

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