A colloidal photonic crystal ink, a colloidal photonic crystal structural color and a preparation method thereof

Abstract

The present application belongs to the technical field of structural color, and particularly relates to a kind of colloidal photonic crystal ink, a kind of colloidal photonic crystal structural color and a preparation method thereof.The preparation method provided by the present application adjusts the surface tension and viscosity of the colloidal photonic crystal ink, so that it is suitable for pattern printing;then, the preparation method of the colloidal photonic crystal structural color provided by the present application uses a substrate treated by hydrophobic treatment (OTS treatment) on one hand, which can reduce the pinning of three-phase line, promote the inward movement of nanoparticles and promote the ordered and close self-assembly;on the other hand, through the method of inverted evaporation self-assembly, the Marangoni flow is enhanced, the inward movement of nanoparticles is promoted, and the ordered and close self-assembly process is promoted, so that the colloidal photonic crystal micro-dome has a higher height-diameter ratio, thereby improving the brightness and saturation of the structural color, and providing a new method for optimizing the color quality of the structural color.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of structural color, and particularly relates to a kind of colloidal photonic crystal ink, a kind of colloidal photonic crystal structural color and a preparation method thereof. BACKGROUND

[0002] Color is an essential part of the world, research shows that humans identify objects first see color and then see shape, apparently humans have processed color information in the unconscious, because humans can distinguish shape, is through the color difference around the contour. From the principle of color formation, it can be mainly divided into two categories of chemical color and structural color. The mechanism of chemical color is mainly due to the selective absorption of natural light by organic molecules and functional groups, while the mechanism of structural color is mainly due to the interaction between light and micro-nano structure, including refraction, reflection, diffraction, interference, etc. At present, scholars are inspired from the biological point of view, and strive to imitate this micro-nano structure, so that it can be applied in display, sensor, anti-counterfeiting and other fields. Photonic crystal is one of the most widely used, which refers to a kind of optical material with periodic variation of refractive index at sub-micron scale. In 1987, John and Yablonovitch proved from the perspective of electromagnetic field that photonic crystal can produce photonic band gap (PBG). Certain wavelengths of light are prohibited to propagate in the photonic band gap, and when the photonic band gap is within 400-800 nm wavelength, structural color will be generated. Although compared with chemical color, structural color has the advantages of color persistence and stability, non-toxic and harmless, green environmental protection, etc., however, due to its great gap in brightness and saturation compared with chemical color, and the patterned preparation is mainly based on template method, which seriously restricts the application of structural color in production and life.

[0003] To enhance the quality of the structural color of photonic crystals, a common method is to dope black substances in the colloidal photonic crystal to absorb scattered light caused by disordered arrangement, for example, Takeoka et al. doped a small amount of carbon black in the silica photonic crystal to improve the saturation of the structural color; Iwata et al. mixed polystyrene beads and cuttlefish ink to obtain a high-saturation amorphous structural color, and the research group also found that the saturation of the structural color was significantly improved by replacing the transparent glass substrate supporting the photonic crystal with a black quartz substrate. Although the above methods improve the saturation of the structural color, they also cause the problem of reduced brightness. In addition, some scholars have also improved the saturation of the structural color by selecting black nanoballs or constructing a core-shell structure, for example, Hu et al. found that adding a silicon shell in SMNPs can further adjust the hue and brightness of the structural color produced thereby; Liu et al. were inspired to prepare SiO2@PDA@GO nanoballs to obtain a lively structural color. Although the above methods have excellent performance, the complex synthesis method often fails to bring sufficient high yield and stability, which will restrict its industrial application. At present, researchers mainly focus on the preparation of materials to improve the saturation and brightness of the structural color, and the research on optimizing the structural color from the structure aspect is relatively lacking. SUMMARY

[0004] The purpose of the present application is to provide a colloidal photonic crystal ink, a colloidal photonic crystal structural color and a preparation method thereof, which optimizes the structural color from the structure aspect, successfully prints a structural color pattern with high brightness and high saturation, and improves the brightness and saturation of the structural color.

[0005] In order to achieve the above purpose, the present application provides the following technical scheme:

[0006] The present application provides a colloidal photonic crystal ink, which comprises carboxylated polystyrene nanoballs, water and ethylene glycol; the volume ratio of the ethylene glycol and the water is 7:3; the mass concentration of the carboxylated polystyrene nanoballs in the colloidal photonic crystal ink is 0.03 g / mL.

[0007] Preferably, the particle size of the carboxylated polystyrene nanoballs is 169-252 nm, the hydration radius is 190-295 nm, and the PDI is ≤0.05.

[0008] Preferably, the preparation method of the carboxylated polystyrene nanoballs comprises the following steps:

[0009] The carboxylated polystyrene nanospheres are obtained by mixing water, alpha-methacrylic acid, sodium linear alkyl benzene sulfonate, sodium bicarbonate, styrene monomer and potassium persulfate in a protective gas atmosphere; the volume ratio of the alpha-methacrylic acid to the styrene monomer is 0.1:5.5.

[0010] The reaction temperature is 70 DEG C, and the reaction time is 8 hours.

[0011] The present application provides a preparation method of colloidal photonic crystal structural color, comprising the following steps: printing droplets on a substrate surface by using the colloidal photonic crystal ink according to the technical scheme; the droplets form a patterned surface on the substrate surface to obtain a patterned substrate.

[0012] The patterned substrate is turned over by 180 DEG, and the patterned surface is inverted downward for evaporation self-assembly to form a colloidal photonic crystal structural color micro-dome unit on the substrate surface, thereby obtaining a colloidal photonic crystal structural color on the substrate surface.

[0013] Preferably, the patterned printing is performed by using a dot mode of an electrohydrodynamic inkjet printing device, and the diameter of each droplet is 200-600 microns.

[0014] Preferably, the electrohydrodynamic inkjet printing is performed under the following conditions: a duty cycle of 50%, a bias voltage of 800 V, an amplitude of 800 V, and a frequency of 200 Hz.

[0015] Preferably, the evaporation self-assembly is performed at a temperature of 30 DEG C and a relative humidity of 60%.

[0016] Preferably, the substrate is a silicon wafer; before the patterned printing, the substrate is subjected to hydrophobic treatment, and the hydrophobic treatment comprises the following steps: performing plasma treatment on the substrate by using oxygen to obtain a plasma-treated substrate.

[0017] The plasma-treated substrate is subjected to hydrophobic treatment by using a hydrophobic treatment reagent, and the hydrophobic treatment reagent comprises an organic solvent and a silane reagent.

[0018] The present application provides a colloidal photonic crystal structural color obtained by the preparation method according to the technical scheme.

[0019] Preferably, the height-diameter ratio of the micro-dome unit is 0.35, and the diameter of the bottom surface of the micro-dome unit is 20-40 microns.

[0020] The present application provides a kind of colloidal photonic crystal ink, including carboxylated polystyrene nanospheres, water and ethylene glycol;The volume ratio of the ethylene glycol and water is 7:3;The mass concentration of the carboxylated polystyrene nanospheres in the colloidal photonic crystal ink is 0.03g / mL.The present application adjusts the proportion of ethylene glycol continuous phase to adjust the viscosity and surface tension of colloidal photonic crystal ink, successfully prints and evaporates self-assembly to form colloidal photonic crystal structure color microdome unit.The colloidal photonic crystal ink provided by the present application improves the brightness of colloidal photonic crystal structure color by 15% to 20% by simple evaporation self-assembly of turning over substrate, and improves the saturation of structural color.

[0021] The present application provides a kind of colloidal photonic crystal structure color preparation method, including the following steps: using the colloidal photonic crystal ink described in the above technical solution to print droplet on the surface of substrate, the droplet forms patterned surface on the surface of substrate, and patterned substrate is obtained;The patterned substrate is turned over 180°, and the patterned surface is inverted downward to evaporate self-assembly, and colloidal photonic crystal structure color microdome unit is formed on the surface of substrate, and colloidal photonic crystal structure color is obtained on the surface of substrate.The present application adjusts the surface tension and viscosity of colloidal photonic crystal ink to make it suitable for patterned printing;Then, the present application enhances Manigol flow by the method of inverted evaporation self-assembly, so that colloidal photonic crystal microdome has higher height-diameter ratio, thereby improving structural color brightness and saturation, and providing a new method for structural color quality optimization.

[0022] The colloidal photonic crystal structure color preparation method provided by the present application can reduce the pinning of three-phase line on one hand by using the substrate after hydrophobic treatment (OTS treatment), promote the inward movement of nanoparticles and promote ordered and close self-assembly;On the other hand, by the method of inverted evaporation self-assembly, Manigol flow is enhanced, the inward movement of nanoparticles is promoted, and the process of ordered and close self-assembly is promoted, so that colloidal photonic crystal microdome has higher height-diameter ratio, thereby improving structural color brightness and saturation, and providing a new method for structural color quality optimization. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Mechanism diagram of upright and inverted droplet evaporation-induced self-assembly colloidal photonic crystal structure color in example 4;

[0024] Figure 2 Observation results of contact angle change in hydrophobic treatment and evaporation self-assembly process in example 4;

[0025] Figure 3 Characterization result graph of colloidal photonic crystal formed by upright droplet and inverted droplet evaporation self-assembly under different hydrophilic and hydrophobic interfaces;

[0026] Figure 4 H / D statistics and morphology observation results of self-assembly colloidal photonic crystal microdome of PS-COOH nano microspheres for electrohydrodynamic inkjet printing

[0027] Figure 5 Fluid simulation results of upside-down droplet and inverted droplet

[0028] Figure 6 Temperature field simulation results of "natural convection field" model and "Manigod flow field" model

[0029] Figure 7 Structural color pattern of colloidal photonic crystal prepared in the embodiment

[0030] Figure 8 Electron microscope characterization results and particle size characterization results of PS-COOH nano microspheres prepared in Example 1

[0031] Figure 9 Fourier infrared light, particle size distribution and surface Zeta potential characterization results of PS-COOH nano microspheres prepared in Example 1

[0032] Figure 10 Physical parameters of colloidal photonic crystal ink prepared in the embodiment under different solvent ratios and colloidal photonic crystal light microscope graphs under different solution ratios

[0033] Figure 11 Electrohydrodynamic inkjet printing physical parameter graph

[0034] Figure 12 Comparison summary graph of microdome structural color of upside-down evaporation self-assembly and inverted evaporation self-assembly in Example 4

[0035] Figure 13 Particle size distribution change and surface Zeta potential change of PS-COOH prepared in Example 1 after two weeks

[0036] Figure 14 Particle image velocimetry (PIV) result graph of upside-down droplet and inverted droplet in Example 4. DETAILED DESCRIPTION

[0037] The present application provides a kind of colloidal photonic crystal ink, including carboxylated polystyrene nano microspheres, water and ethylene glycol;The volume ratio of the ethylene glycol and water is 7:3;The mass concentration of the carboxylated polystyrene nano microspheres in the colloidal photonic crystal ink is 0.03g / mL.

[0038] In the present application, all preparation raw materials / components are commercially available products well known to those skilled in the art unless otherwise specified.

[0039] The colloidal photonic crystal ink provided by the application comprises carboxylated polystyrene (PS-COOH) nanospheres. In the application, the particle size of the carboxylated polystyrene nanospheres is preferably 169-252 nm, the hydrated radius is preferably 190-295 nm, and the PDI is preferably ≤0.05. The Zeta potential of the carboxylated polystyrene nanospheres is preferably -29.2 to -25.4 mV.

[0040] In the application, the preparation method of the carboxylated polystyrene nanospheres preferably comprises the following steps:

[0041] In a protective gas atmosphere, water, α-methacrylic acid, sodium linear alkyl benzene sulfonate, sodium bicarbonate, styrene monomer and potassium persulfate are mixed to react to obtain the carboxylated polystyrene nanospheres. In the application, the water is preferably ultrapure water. Before the mixing, the application preferably washes the styrene monomer in a solid-phase extraction column containing basic alumina to remove the polymerization inhibitor in the styrene monomer raw material. The number of washing is preferably 3 times. The volume ratio of the water to the styrene monomer is 60:5.5. The volume ratio of the α-methacrylic acid to the styrene monomer is preferably 0.1:5.5. The mass ratio of the sodium linear alkyl benzene sulfonate to the volume of the styrene monomer is preferably 13.2 mg:5.5 mL. The mass ratio of the sodium bicarbonate to the volume of the styrene monomer is preferably 28.2 mg:5.5 mL. The potassium persulfate is preferably used in the form of a potassium persulfate aqueous solution, and the mass concentration of the potassium persulfate aqueous solution is preferably 0.5 mg / mL. The volume ratio of the potassium persulfate aqueous solution to the styrene monomer is 1:5.5. The mixing sequence is preferably as follows: in a protective gas atmosphere, water, α-methacrylic acid, sodium linear alkyl benzene sulfonate and sodium bicarbonate are premixed to obtain a premixing liquid; after the premixing liquid is warmed to 60℃, the styrene monomer is added, and after oxygen is removed, potassium persulfate is added. The mixing is carried out under stirring, and the stirring is preferably magnetic stirring, and the stirring speed is preferably 300 r / min. The reaction temperature is 70℃, and the reaction time is 8 h. The above protective gas is preferably nitrogen. After the reaction is completed, the application preferably carries out solid-liquid separation on the obtained reaction liquid to obtain a solid phase product, and after the solid phase product is washed with water, the carboxylated polystyrene nanospheres are obtained. The solid-liquid separation is preferably centrifugal separation, the centrifugal separation speed is preferably 13000 rpm, and the centrifugal separation time is preferably 20 min. The application preferably oscillates and disperses the PS-COOH nanospheres in water for storage.

[0042] The colloidal photonic crystal ink provided by the application comprises water.

[0043] The colloidal photonic crystal ink provided by the application comprises ethylene glycol.

[0044] In the present application, the volume ratio of the ethylene glycol and water is preferably 7:3. The mass concentration of the carboxylated polystyrene nanospheres in the colloidal photonic crystal ink is preferably 0.03 g / mL.

[0045] The present application provides a preparation method of the colloidal photonic crystal ink as described in the above technical solution, comprising the following steps:

[0046] The PS-COOH nanosphere aqueous dispersion and ethylene glycol are mixed to obtain the colloidal photonic crystal ink.

[0047] In the present application, the solid content of the PS-COOH nanosphere aqueous dispersion is preferably 10%. The volume ratio of the PS-COOH nanosphere aqueous dispersion and ethylene glycol is preferably 3:7. The mixing is preferably ultrasonic oscillation. The time of the ultrasonic oscillation is preferably 30 min. The prepared colloidal photonic crystal ink is preferably placed in a constant temperature and humidity chamber with a temperature of 30℃ and a relative humidity RH of 60% for storage. Before each use, ultrasonic dispersion is performed for 10 min.

[0048] The present application provides a preparation method of a colloidal photonic crystal structural color, comprising the following steps: printing droplets on a substrate surface by using the colloidal photonic crystal ink as described in the above technical solution, the droplets forming a patterned surface on the substrate surface to obtain a patterned substrate;

[0049] The patterned substrate is turned over by 180°, and the patterned surface is inverted downward for evaporation self-assembly, forming a colloidal photonic crystal structural color micro-dome unit on the substrate surface, and obtaining a colloidal photonic crystal structural color on the substrate surface.

[0050] The colloidal photonic crystal ink in the application is used to print liquid drops on the surface of a substrate, and the liquid drops form a patterned surface on the substrate to obtain a patterned substrate. In the application, the substrate is preferably a silicon wafer. Before the patterned printing, the substrate is subjected to hydrophobic treatment, which comprises the following steps: subjecting the substrate to plasma treatment with oxygen to obtain a plasma-treated substrate; and subjecting the plasma-treated substrate to hydrophobic treatment with a hydrophobic treatment reagent, which comprises an organic solvent and a silane reagent. Before the plasma treatment of the substrate, the application preferably further comprises the following steps: placing a cut and polished substrate into an aiptasia solution to remove organic impurities remaining on the surface of the silicon wafer, then repeatedly washing with deionized water, and blowing dry with high-purity nitrogen, and placing into a culture dish for standby. The plasma treatment is preferably performed under the following conditions: the power is preferably 100 W, and the treatment time is preferably 300 s. The organic solvent is preferably cyclohexane. The silane reagent is preferably octadecyltrichlorosilane (OTS). The volume ratio of the organic solvent to the silane reagent in the hydrophobic treatment reagent is preferably 1:100. The hydrophobic treatment is preferably performed at room temperature for 24 h under static conditions. After the hydrophobic treatment, the application preferably sequentially washes the treated substrate with tetrahydrofuran, ethanol, and water. The tetrahydrofuran washing is preferably performed under ultrasonic conditions for 15 minutes. The tetrahydrofuran washing can remove unreacted alkyl groups and hydrolysis products on the surface of the treated substrate.

[0051] In the application, the patterned printing is preferably performed in the dot mode of an electrohydrodynamic inkjet printing device. The electrohydrodynamic inkjet printing is preferably performed under the following conditions: the duty cycle is preferably 50%, the bias voltage is preferably 800 V, the amplitude is preferably 800 V, and the frequency is preferably 200 Hz. The diameter of each drop of liquid obtained by printing is preferably 200-600 μm, more preferably 200-500 μm, and most preferably 350-400 μm. In the application, liquid drops with a diameter of 200-300 μm are too small, the evaporation self-assembly speed is too fast, and the structural color brightness is not high; liquid drops with a diameter of 400-600 μm are too sensitive to disturbance, and the structural color is prone to be scattered and not concentrated. In the application, liquid drops with a diameter of 200-600 μm can form a good structural color, and liquid drops with a diameter of 350-400 μm form the best structural color.

[0052] In the specific embodiment of the present application, the specific implementation of the patterned printing is preferably: using an electrohydrodynamic inkjet printing device, using a syringe to suck the colloidal photonic crystal ink into a precision capillary glass tube, then fixing the capillary glass tube, connecting a copper wire to the positive pole of a high-voltage power supply, adjusting the distance between the capillary glass tube and the substrate to a suitable distance, and applying voltage printing, wherein the bias voltage is 800 V, the amplitude is 800 V, the frequency is 200 Hz, and the duty cycle is 50%.

[0053] After obtaining the patterned substrate, the present application turns the patterned substrate upside down by 180°, inverts the patterned surface downward for evaporation self-assembly, forms a colloidal photonic crystal structural color micro-dome unit on the surface of the substrate, and obtains a colloidal photonic crystal structural color on the surface of the substrate. In the present application, the temperature of the evaporation self-assembly is preferably 30°C, and the relative humidity is preferably 60%.

[0054] The present application provides a colloidal photonic crystal structural color prepared by the preparation method described in the above technical solution, and the colloidal photonic crystal structural color is composed of micro-dome units. In the present application, the height-diameter ratio of the micro-dome unit is preferably 0.35. The bottom surface diameter of the micro-dome unit is preferably 20-40 μm.

[0055] In order to further illustrate the present application, the technical solutions provided by the present application are described in detail below in combination with examples, but they should not be understood as limiting the scope of protection of the present application.

[0056] Example 1

[0057] Synthesis and characterization of PS-COOH

[0058] Synthesis: PS-COOH nanospheres were prepared by emulsion polymerization. Before the reaction, the styrene monomer was repeatedly washed three times in a solid-phase extraction column containing basic alumina to remove the polymerization inhibitor in the raw material for standby. Before the reaction, 60 mL of ultrapure water, 0.1 mL of a-methacrylic acid, 13.2 mg of sodium linear alkyl benzene sulfonate (LAS), and 28.2 mg of NaHCO3 were added to a three-necked flask. A magnetic stirrer was placed in the three-necked flask, and a nitrogen tube, a reflux condenser, and an anti-suckback gas washing bottle were connected to the three ports, respectively. The stirring speed was set to 300 r / min, the temperature was raised to 60°C, and then the styrene monomer (the addition volume of the styrene monomer was 4.88 mL, 5.19 mL, and 5.47 mL, respectively) was added, and nitrogen was introduced for 30 min to remove the oxygen in the device. Subsequently, 1 mL of potassium persulfate (KPS) with a concentration of 0.5 mg / mL was added, and the temperature was raised to 70°C under nitrogen protection, and the reaction was carried out for 8 h. Finally, the white emulsion obtained in the reaction was centrifuged at 13,000 rpm for 20 min, and clear color patterns were observed on the wall of the centrifuge tube. The obtained centrifugal precipitate was washed with deionized water three times to obtain PS-COOH nanospheres, and finally the PS-COOH nanospheres were dispersed in water and stored by oscillation.

[0059] Characterization:

[0060] The electron microscope characterization results and particle size characterization results of the PS-COOH nanospheres prepared in this example are shown in Figure 8 Figure 8 In a, b, and c of, a, b, and c are the electron microscope characterization results of three particle sizes of PS-COOH nanospheres prepared in this example when the addition volume of the styrene monomer is 4.88 mL, 5.19 mL, and 5.47 mL, respectively. In this example, the sample 1 of PS-COOH nanospheres is obtained when the addition volume of the styrene monomer is 4.88 mL, the sample 2 of PS-COOH nanospheres is obtained when the addition volume of the styrene monomer is 5.19 mL, and the sample 3 of PS-COOH nanospheres is obtained when the addition volume of the styrene monomer is 5.47 mL. Figure 8 a and d in are the detection results of sample 1, Figure 8 b and e in are the detection results of sample 2, Figure 8 c and f in are the detection results of sample 3. From Figure 8 a, b, and c in , it can be seen that the PS-COOH nanospheres synthesized in this example are round and uniform in size. Figure 8 d, e, and f in are the particle size characterization results of the PS-COOH nanospheres prepared in this example by Malvern laser particle size analyzer, and from Figure 8 d, e, and f in , it can be seen that the coefficient of variation of the PS-COOH nanospheres synthesized in this example is less than 0.05, indicating that they have good uniformity.

[0061] In this embodiment, PS-COOH nanospheres were compared with PS nanospheres. The preparation method of PS nanospheres was as follows: before the reaction, the styrene monomer was repeatedly washed three times in a solid-phase extraction column containing basic alumina to remove the polymerization inhibitor in the raw material for standby use. Before the reaction started, 60 mL of ultrapure water, 13.2 mg of linear alkyl benzene sulfonate sodium (LAS), and 28.2 mg of NaHCO3 were added to a three-necked flask. A magnetic stirrer was placed in the three-necked flask, and a nitrogen tube, a condensation reflux tube, and an anti-suckback gas washing bottle were connected to the three ports of the three-necked flask, respectively. The stirring speed was set to 300 r / min, and the temperature was raised to 60°C, and then 5.5 mL of styrene monomer was added, and nitrogen was introduced for 30 minutes to remove the oxygen in the device. Subsequently, 1 mL of potassium persulfate (KPS) with a concentration of 0.5 mg / mL was added, and the temperature was raised to 70°C under nitrogen protection, and the reaction was carried out for 8 h. Finally, the white emulsion obtained by the reaction was centrifuged at 13000 rpm for 20 min, and clear color patterns were observed on the wall of the centrifuge tube. The obtained centrifugal precipitate was washed with deionized water three times to obtain PS nanospheres, and finally the PS nanospheres were dispersed in water and stored by oscillation.

[0062] Figure 9 The Fourier infrared spectrum of PS and PS-COOH sample 3 in a is shown in the following figure: Figure 9 The particle size distribution and surface Zeta potential of PS and PS-COOH sample 2 in b are compared in the following figure: Figure 9 As shown in a, the PS-COOH nanospheres prepared in this embodiment have vibration peaks at 1708 cm -1 and 3450 cm -1 , which correspond to the stretching vibration peak of C=O and the stretching vibration peak of the hydroxyl group in the carboxylic acid, respectively, indicating the presence of carboxyl groups on the surface of the PS-COOH nanospheres. Figure 9 The upper graph of b shows the particle size distribution of PS and PS-COOH, which shows that the introduction of carboxyl groups has little effect on the particle size of polystyrene. Figure 9 The lower graph of b shows the comparison of the surface Zeta potential of PS and PS-COOH, which shows that the introduction of carboxyl groups increases the surface potential Zeta of polystyrene, which also proves the introduction of carboxyl groups.

[0063] The embodiment introduces carboxyl groups to modify the surface of PS nanospheres (PS-COOH), increases the surface Zeta potential, and makes the obtained PS-COOH nanospheres form ordered arrangement structures as much as possible in the process of evaporation self-assembly, so as to realize the goal of obtaining high-quality structural colors. Therefore, the application adds an appropriate amount of methyl methacrylate monomer (alpha-methyl methacrylate) to the raw materials. The application can react PS to PS-COOH by introducing alpha-methyl methacrylate, that is, introducing carboxyl groups on the surface of polystyrene nanospheres. The significance of introducing carboxyl groups in the application is to improve the surface Zeta potential of polystyrene. The advantage is that the stability of the colloidal photonic crystal ink can be ensured. The stability comparison results of PS nanospheres and PS-COOH nanospheres (sample 2) in the embodiment are shown in Figure 13 , Figure 13 a in the table is the particle size distribution change and surface Zeta potential change of the colloidal solution prepared after two weeks of dispersion of PS nanospheres in water; Figure 13 b in the table is the particle size distribution change and surface Zeta potential change of the colloidal solution prepared after two weeks of dispersion of PS-COOH nanospheres in water. It can be known from the table that Figure 13 the introduction of carboxyl groups can make the PS-COOH nanospheres more stable in water (the colloidal photonic crystal ink obtained later).

[0064] The performance parameters of the PS-COOH nanospheres prepared in the embodiment are shown in Table 1.

[0065] Table 1 Performance parameters of PS-COOH nanospheres prepared in Example 1

[0066] Sample Particle size Hydrodynamic radius Zeta potential PDI PS-COOH Sample 1 169 nm 190 nm -25.4 mV 0.05 PS-COOH Sample 2 215 nm 255 nm -28.5 mV 0.03 PS-COOH Sample 3 252 nm 295 nm -29.2 mV 0.03

[0067] Example 2

[0068] A sample 2 of PS-COOH nanospheres prepared in Example 1 was dispersed in water and ethylene glycol to obtain a colloidal photonic crystal ink. The volume ratio of water to ethylene glycol was configured as 0:10, 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1 or 10:0, respectively, to obtain colloidal photonic crystal inks with different solvent ratios. Except for the volume ratio of water to ethylene glycol being 0:10 and 10:0, the colloidal photonic crystal ink was prepared as follows: the sample 2 of PS-COOH nanospheres prepared in Example 1 was dispersed in water (solid content of 10%, PS-COOH nanosphere colloidal aqueous solution), and then ethylene glycol was added according to different volume ratios of water to ethylene glycol to obtain colloidal photonic crystal inks with different solvent ratios.

[0069] The colloidal photonic crystal inks with different solvent ratios prepared in this example were characterized.

[0070] Figure 10 The physical parameters of the colloidal photonic crystal inks with different solvent ratios prepared in this example and the colloidal photonic crystal optical microscope images of different solution ratios are shown in FIGS. 1-8. Figure 10 (a) in FIGS. 1-8 is the surface tension and viscosity diagram of the colloidal photonic crystal ink with different volume ratios of ethylene glycol to water; Figure 10 (b) in FIGS. 1-8 is the Oh number of the colloidal photonic crystal ink with different volume ratios of ethylene glycol to water; Figure 10 (c) in FIGS. 1-8 is the colloidal photonic crystal optical microscope image of the droplet evaporation self-assembly with different volume ratios of ethylene glycol to water (scale: 20 μm).

[0071] In this example, the PS-COOH nanospheres sample 2 synthesized in Example 1 was dispersed in water (10% solid content) and patterned printing was performed by the dotting mode of the electrohydrodynamic inkjet printing device. Because water has a high surface tension and a low viscosity (70 mN / m and 1 mPa·s), a larger electric field force is required to form a Taylor cone to break through the surface tension barrier, however, under the action of a high electric field force, the printing droplet is prone to collapse and the solution is prone to atomization. In addition, the self-assembly time of the PS-COOH nanospheres in the droplet also affects the quality of the finally formed structural color, when the self-assembly time is insufficient, more cracks and cavities are prone to form to release stress energy. Therefore, in this example, a solvent with a low surface tension and a high boiling point is added to adjust the fluid properties of the photonic colloidal ink. In this example, the surface tension of the photonic colloidal ink is adjusted by adding an appropriate amount of ethylene glycol, and the high boiling point of the ethylene glycol solution can provide sufficient time for the PS-COOH to form a tightly ordered structure during the evaporation self-assembly process.

[0072] In the electrohydrodynamic inkjet printing process, the formation of droplets is a very complex process, and the present application introduces some dimensionless physical constants to assist in the study of the rheological properties of the ink. For electrohydrodynamic inkjet printing, the present application uses the electric Bond number (BoE) to relate the electric field force and the surface tension, and uses the Reynolds number (Re), the Weber number (We) and the Ohnesorge number (Oh) to characterize the fluid properties. The expressions of the above parameters are shown in Formula 1, Formula 2, Formula 3 and Formula 4:

[0073]

[0074]

[0075]

[0076]

[0077] wherein is the voltage applied to the nozzle, H is the nozzle height, the corresponding value in the experiment is 0.2 mm, R is the nozzle radius, the precision glass head radius used in the experiment is 22.5 μm. ρ represents the density of the fluid, γ represents the surface tension of the fluid, η represents the dynamic viscosity of the fluid, v represents the velocity of the ink droplet, and a represents the characteristic length. The electric Bond number represents the ratio of the characteristic electric field force to the surface tension effect on the fluid, the Reynolds number represents the ratio of the inertial force to the viscous force in the fluid motion, the Weber number represents the ratio of the inertial force to the surface tension effect, and the Ohnesorge number combines the Reynolds number and the Weber number, and describes the relationship between the viscous force, the inertial force and the surface tension. From the electric Bond number, it can be known that under the condition that the device operating parameters are certain, the smaller the surface tension, the more easily the fluid is ejected from the nozzle.

[0078] Secondly, the present application considers the influence of satellite droplets, which can be estimated by the following formula 5 to estimate the radius of satellite droplets generated by surface tension shrinkage:

[0079]

[0080] In formula 5, τ represents the characteristic time of droplet breakage, and under the condition of ignoring gravity and keeping the electric Bond number constant, τ is generally The change range is small, and it can be considered as a constant. Therefore, the present application finds that the radius of satellite droplets is approximately inversely proportional to the Oh number. Therefore, the present application considers using a continuous phase with a larger Oh number to configure the PS-COOH photonic colloidal ink (colloidal photonic crystal ink).

[0081] In order to determine the volume ratio of water and ethylene glycol in the specific colloidal photonic crystal ink, the present application tests the viscosity and surface tension of the PS-COOH photonic colloidal ink with different proportions of ethylene glycol, and calculates the Oh number corresponding to each component, and the results are shown in (a) and (b) of Figure 10 It can be seen that as the volume ratio of ethylene glycol increases, the Oh number of the photonic colloidal ink also gradually increases. According to the above analysis, the present application should select the component with the largest proportion of ethylene glycol as the continuous phase of the photonic colloidal ink. However, it is found in actual experiments that when the proportion of PS-COOH is too low, a large number of PS-COOH nanospheres are easily adsorbed on the surface of the silicon substrate due to electrostatic interaction, forming a chaotic order and forming a structural color with poor quality, as shown in (c) of Figure 10 Ethylene glycol Solution The ratio of the volume of water in the ink to the volume of ethylene glycol, that is, the ratio of V Solution It can be seen that the center of the structural color bright spot appears and gradually brightens, and then a circular ring appears from the bright spot. This may be related to the self-assembly time of the nanoparticles in the droplet. In addition to the nanoparticles captured by the capillary flow and the substrate during movement, the remaining nanoparticles self-assemble during the evaporation process to present the structural color. When the mass fraction of nanoparticles in the droplet exceeds a certain threshold, the ordered structure cannot completely converge during the evaporation process, and finally a circular ring structure is formed. Therefore, based on the above experimental phenomena, the present embodiment finally determines that the ratio of the photonic colloidal ink is 7:3. Ethylene glycol Solution

[0082] Example 3

[0083] Electrofluidic device parameters

[0084] ​​​​Since the printable area of electrohydrodynamic inkjet printing is a nonlinear area, the related parameters (bias, amplitude, frequency, duty cycle) are explored in this embodiment. The bias voltage represents the average of the sum of the peak voltage and the valley bottom voltage in a pulse wave; the amplitude represents the difference between the peak voltage and the valley bottom voltage; the frequency is used to describe the duration of a pulse cycle; the duty cycle represents the proportion of the peak voltage in a pulse cycle. Considering the physical meaning of the four variables, the following simplifications are made in this embodiment. First, the bias voltage and the amplitude voltage are simplified to keep them equal, represented by the equivalent voltage Veq. Second, it is found in the study that the duty cycle has a significant effect on the size of the droplet when it is less than 50%, and when the duty cycle is greater than 50%, the size of the main droplet does not change significantly, so the duty cycle is selected to be 50% in this embodiment. In summary, the relationship between the equivalent voltage and the frequency also needs to be studied.

[0085] Figure 11 The physical parameter diagram of electrohydrodynamic inkjet printing is shown in FIG. 1a, where a is the printing area phase diagram under different frequencies and equivalent voltages (scale in the insert: 20 μm); and b is the physical parameter diagram of electrohydrodynamic inkjet printing in the experiment. Figure 11 Figure 11

[0086] In an ideal case, the droplet obtained by the present application is expected to be free of satellite droplets, and the surface tension of the main droplet liquid film is greater than the electric field force exerted on the liquid film by the electric field, so that the main droplet can exist stably. To this end, the present embodiment uses the control V Ethylene glycol / Vsolution The ratio of the photonic colloidal ink is 7:3, and the phase diagram is drawn by changing the frequency and the equivalent voltage Veq, as shown in FIG. 1a. Through the phase diagram, it can be found that, under the same equivalent voltage Veq, there is a starting frequency (red line) and a cutoff frequency (black line). When the frequency is greater than the starting frequency, it means that the frequency is too fast, and the relaxation of the fluid itself causes the droplet to be unable to break through the constraint of the surface tension and fall. When the frequency is less than the cutoff frequency, in addition to forming a main droplet, a large number of satellite droplets are also formed, forming an unstable beam, which affects the resolution of the structural color pattern, as shown in region B of FIG. 1a. Therefore, the device parameters of the present embodiment should be controlled within region A, so as to achieve the purpose of forming a single droplet. Figure 11 Figure 11 Figure 11 b is a schematic diagram of the pulse voltage used in the present embodiment, where the bias voltage is 800 V, the amplitude is 800 V, the frequency is 200 Hz, and the duty cycle is 50%.

[0087] Embodiment 4

[0088] (1) Hydrophobic treatment of silicon wafer substrate​​​​

[0089] First, piranha solution is configured, cut polished silicon wafer is put into it for 10s to remove organic impurities remaining on the surface of the silicon wafer, then repeatedly washed with deionized water, and dried with high-purity nitrogen, and placed in a culture dish for standby. The treated silicon wafer is placed in a plasma treatment chamber, oxygen is introduced, the power is set to 100W, and the treatment is performed for 300s. At this time, the silicon wafer surface has a large number of hydroxyl groups. Subsequently, the present application places the silicon wafer in a glass culture dish (not a plastic culture dish), adds cyclohexane and OTS (the volume ratio of the two is 1:100), and stands at room temperature for 24h, noting that the silicon wafers should not overlap each other as much as possible. Then, the present application takes out the silicon wafer and ultrasonically treats it in a tetrahydrofuran solution for 15 minutes to remove unreacted alkyl and hydrolysis products. Finally, after washing with ethanol and deionized water three times and wiping with a dust-free paper, the silicon wafer is placed in a culture dish for standby.

[0090] (2) Preparation of PS-COOH colloidal photonic crystal ink

[0091] Take the dispersed PS-COOH sample 2 aqueous solution 3mL (solid content 10%) prepared in Example 1, and add ethylene glycol solution 7mL, ultrasonically shake for 30min, and place the prepared colloidal photonic crystal ink in a constant temperature and humidity environment with a temperature of 30℃ and a relative humidity RH of 60%. Before each use, ultrasonically disperse for 10min.

[0092] (3) Electrowetting inkjet printing patterning

[0093] An electrowetting inkjet printing device is used to make a colloidal photonic crystal hemispherical dome structure color pattern. A syringe is used to suck about 1mL of colloidal photonic crystal ink into a precision capillary glass tube. Then the capillary glass tube is fixed, and the copper wire is connected to the positive electrode of a high-voltage power supply, the capillary glass tube and the substrate are adjusted to a suitable distance, and the voltage is applied for printing, wherein the bias voltage is 800V, the amplitude is 800V, the frequency is 200Hz, the duty cycle is 50%, and the droplet diameter for printing is 350μm-400μm.

[0094] Finally, the printed silicon wafer is placed in a constant temperature and humidity environment with a temperature of 30 DEG C and a relative humidity RH of 60% for evaporation self-assembly, wherein the evaporation self-assembly includes two modes of upright evaporation self-assembly and inverted evaporation self-assembly, wherein the upright evaporation self-assembly only needs to place the normally printed silicon wafer on a horizontal surface; the inverted evaporation self-assembly needs a hollow horizontal shelf with support around the shelf, so that the normally printed silicon wafer is turned over by 180 DEG and placed on the horizontal shelf. During the evaporation self-assembly process, the humidity and temperature of the environment specifically affect the self-assembly speed of the PS-COOH nanospheres in the droplets, and the constant temperature and humidity environment with a temperature of 30 DEG C and a relative humidity RH of 60% is beneficial to the formation of ordered structures by self-assembly.

[0095] Figure 7 The colloidal photonic crystal structure color pattern prepared in the embodiment. Figure 7 (a), (b), (c) and (d) in the figure are colloidal photonic crystal structure color patterns formed by upright evaporation self-assembly; Figure 7 (e), (f), (g) and (h) in the figure are colloidal photonic crystal structure color patterns formed by inverted evaporation self-assembly.

[0096] The present application simulates the changes of fluid field in upright and inverted droplets by constructing an evaporation self-assembly model by COMSOL software, and the simulation results are very consistent with the experimental results. Finally, the present application selects a microdome with a suitable diameter as a patterning unit by comparing microdomes with different diameters, and the feasibility of the above method is intuitively explained by patterning printing, which provides a new idea for the optimization of structural color. In the present application, when the colloidal photonic crystal ink is patterned and printed on the surface of the substrate, the diameter of each droplet is 200-400 mu m. When the droplet point is too small, the evaporation speed is fast and it is difficult to self-assemble, and when the droplet point is too large, the resolution of the overall pattern is reduced.

[0097] Figure 1 Mechanism diagram of the colloidal photonic crystal structure color formed by upright and inverted droplet evaporation-induced self-assembly in embodiment 4.

[0098] In the present application, the key to the formation of high-quality structural color lies in whether the PS-COOH nanospheres in the droplets generated by electrohydrodynamic inkjet printing can form ordered hemispherical micro-domes in the evaporation-induced self-assembly process. In the process of evaporation-induced self-assembly, the common coffee ring effect is the main obstacle to the formation of ordered hemispherical structures. For untreated hydrophilic interfaces, the pinned three-phase line causes more stress concentration, resulting in the appearance of cracks and vacancies. At the same time, under the action of capillary force, nanoparticles tend to accumulate at the edge of the droplet, forming a coffee ring, which affects the quality of the final structural color. In the prior art, scholars often perform hydrophobic treatment on the silicon substrate or change the structure of the three-phase interface, so that the droplet on the treated silicon substrate has a larger contact angle and receding angle. At this time, the pinned three-phase line becomes a slidable three-phase line and slides inward, promoting the concentration of nanospheres in the droplet inward and avoiding accumulation at the edge of the droplet, thereby minimizing the impact of the coffee ring effect, so as to obtain high-quality structural color. However, in order to form excellent structural color, the common method is to dope black substances in the colloidal photonic crystal to absorb scattered light due to disordered arrangement. Although this method improves the saturation of structural color, it also causes the problem of reduced brightness. In addition, some scholars also choose black nanospheres or construct core-shell structures to improve the saturation of structural color. Although this method has excellent performance, the complex synthesis method often fails to bring sufficient high yield and stability, which restricts its industrial application.

[0099] On the basis of hydrophobic treatment, the present application only performs inverted evaporation treatment on the droplet in the evaporation-induced self-assembly process, and finds that the brightness of the structural color is improved and the saturation is increased.

[0100] Figure 2 For the observation results of the contact angle change in the hydrophobic treatment and evaporation self-assembly process in Example 4, Figure 2 (a) in the figure is a schematic diagram of hydrophobic treatment of a silicon substrate; Figure 2 (b) in the figure is a real-time diagram of droplet evaporation on an untreated substrate, a plasma-treated substrate and an OTS hydrophobic-treated substrate; Figure 2 (c), (d) and (e) in the figure are respectively the droplet evaporation contact angle change diagrams on the untreated substrate, the plasma-treated substrate and the OTS hydrophobic-treated substrate.

[0101] In Example 4, the silicon substrate is hydrophobically treated with a silane reagent (octadecyltrichlorosilane, OTS) to obtain a hydrophobic surface interface. The hydrophobic treatment process in Example 4 is shown in (a) in the figure. Figure 2 In order to clarify the influence of different hydrophilic and hydrophobic interfaces on the evaporation process, the present application performs real-time observation on the evaporation process of the droplet on the untreated silicon substrate, the plasma-treated silicon substrate and the OTS-treated silicon substrate in Example 4 as shown in the figureFigure 2 As shown in (b), it can be observed that the contact angles of the droplets at different hydrophilic and hydrophobic interfaces, from smallest to largest, are: plasma-treated silicon substrate, untreated silicon substrate, and OTS-treated silicon substrate. After plasma treatment, the contact angle of the droplets significantly decreases; after hydrophobic treatment, the contact angle of the droplets significantly increases. This is because during plasma treatment, oxygen is converted into ozone under ultraviolet light, which strongly oxidizes the silicon wafer, ultimately existing as hydroxyl groups on the treated surface. Hydroxyl groups are hydrophilic groups, thus reducing the contact angle of the droplets. During hydrophobic treatment, chlorine atoms in the OTS react with the hydroxyl groups on the silicon wafer surface, successfully attaching silane chains to the silicon wafer surface. The hydrophobic silane chains increase the contact angle of the droplets. Example 4 of this invention further measures the changes in the contact angle of the droplets during evaporation through real-time photography, and the results are as follows: Figure 2 As shown in (c), (d), and (e) of the diagram. This invention found that for droplets of the same volume, the contact angle is positively correlated with the evaporation time; the larger the contact angle, the longer the evaporation time. For hydrophilic surfaces, the evaporation times of upright and inverted droplets are comparable. However, for hydrophobic surfaces, the evaporation time of inverted droplets is significantly longer than that of upright droplets. This may be because at hydrophobic interfaces, evaporating gases are more easily concentrated at the interface between the droplet and the silicon wafer, resulting in higher humidity and inhibiting evaporation. Simultaneously, from... Figure 3 As shown in (e), the three-phase line migration time of the inverted droplet is longer than that of the upright droplet, resulting in a delayed aging due to the pinning effect. This indicates that, for the same droplet volume, the nanoparticle hemispherical structure ultimately formed by the inverted droplet is more concentrated and ordered. This is also one of the reasons why, after inversion, the ordered hemispherical structural color can form a higher quality structural color.

[0102] Example 4 of this invention observed the colloidal photonic crystal structure after droplet evaporation and self-assembly on different hydrophilic and hydrophobic silicon wafer substrates, such as... Figure 3 As shown. Figure 3 Optical mirror images of colloidal photonic crystals formed by the evaporation and self-assembly of upright and inverted droplets at different hydrophilic and hydrophobic interfaces. Figure 3 In Figure 'a', the optical mirror images (scale bar: 20 μm) show the self-assembly of upright and inverted droplets into colloidal photonic crystals on untreated silicon substrates, plasma-treated silicon substrates, and OTS-treated silicon substrates. Figure 3 In the figure, b represents the micro-area reflectance spectral results of colloidal photonic crystals formed by the evaporation and self-assembly of upright and inverted droplets on untreated silicon substrates, plasma-treated silicon substrates, and OTS-treated silicon substrates. Figure 3 In the diagram, 'c' represents the CIE diagram showing the self-assembly of upright and inverted droplets into colloidal photonic crystals on untreated silicon substrates, plasma-treated silicon substrates, and OTS-treated silicon substrates.Figure 4 It can be seen that only low-brightness structural color halos appear on untreated silicon substrates and plasma-treated silicon substrates, while after OTS treatment, inverted droplets show a more obvious bright spot at the center of the structural color than upright droplets. However, comparing the two, this invention shows that inverted droplets are more likely to shrink inward than upright droplets, which is consistent with the phenomenon observed in this invention during the evaporation process. Furthermore, nanoparticles are more likely to form an ordered arrangement structure during movement, producing a green structural color halo.

[0103] Figure 4 Statistical analysis of the H / D ratio and morphological observation of self-assembled colloidal photonic crystal microdomes of PS-COOH nanospheres printed by electrofluid inkjet printing. Figure 4 (a) and (b) are SEM images of the side views of the self-assembled colloidal photonic crystal microdome of the droplets, which are upright and inverted, respectively. Figure 4 (c) in the figure shows the H / D statistics of self-assembled colloidal photonic crystal microdomes of upright and inverted droplet evaporation. Figure 4 (d) is a top-view SEM image of the self-assembled colloidal photonic crystal from an upright droplet (scale bar: 10 μm). Figure 4 (e) in the figure is a cross-sectional view of an upright droplet evaporating and self-assembling colloidal photonic crystal cut by FIB at low magnification (scale bar: 5μm); Figure 4 (f) and (g) in the image are cross-sectional views of an upright droplet evaporating and self-assembling colloidal photonic crystal cut by FIB at high magnification (scale bar: 1 μm); Figure 4 (h) is a top-view SEM image of the self-assembled colloidal photonic crystal from the evaporation of an inverted droplet (scale bar: 10 μm); Figure 4 (i) is a cross-sectional view of an inverted droplet evaporating and self-assembling colloidal photonic crystal cut by FIB at low magnification (scale bar: 5μm); Figure 4 In the diagram, (j) and (k) are cross-sectional views of an inverted droplet evaporating and self-assembling colloidal photonic crystal cut by FIB at high magnification (scale bar: 1 μm).

[0104] To investigate the differences in the formation of colloidal photonic crystal hemispherical microdome structures by upright and inverted droplets during evaporation and self-assembly, and to further explore the reasons for these differences, this invention observes the microstructure of the colloidal photonic crystal hemispherical microdome, such as... Figure 4 As shown. Comparison Figure 4 (a) and Figure 4The H / D of the inverted droplet evaporation self-assembly to form the colloidal photonic crystal hemispherical micro-dome is 0.35, and the H / D of the upright droplet evaporation self-assembly to form the colloidal photonic crystal hemispherical micro-dome is 0.29. Meanwhile, the present application also observes and measures other different diameter sizes of the upright and inverted colloidal photonic crystal hemispherical micro-domes. It is found that when the inverted evaporation measure is taken, for the same diameter size of the droplet, the colloidal photonic crystal hemispherical micro-dome formed has a higher H / D value, which also explains why after the inversion, a higher quality structural color can be formed.

[0105] In addition, the present application carries out FIB cutting on the upright and inverted evaporation self-assembly to form the colloidal photonic crystal hemispherical micro-dome, and observes the order degree of the surface and the inside, as shown in (d), (e), (f), (g), (h), (i), (j) and (k) of Figure 5 The present application finds that the upright and inverted evaporation self-assembly to form the colloidal photonic crystal hemispherical micro-dome both appear obvious ordered and disordered regions, and for the most surface interface, both form an ordered layer, which is also the structural source of the structural color. And in the inside of the colloidal photonic crystal, the nanoparticles mainly present in a disordered manner. This is related to the Brownian motion of the nanoparticles in the fluid. Compared with the nanoparticles on the surface being captured by the gas-liquid interface, the nanoparticles in the inside are more likely to keep moving under the action of the internal flow field.

[0106] Simulation analysis:

[0107] Figure 5 The fluid simulation results of the upright droplet and the inverted droplet. Figure 5 The temperature distribution diagram of the upright droplet is (a); Figure 5 The fluid velocity field distribution diagram of the upright droplet “Marangoni convection + natural convection” is (b); Figure 5 The fluid velocity field distribution diagram of the upright droplet “Marangoni convection” is (c); Figure 5 The fluid velocity field distribution diagram of the upright droplet “natural convection” is (d); Figure 5 The temperature distribution diagram of the inverted droplet is (e); Figure 5 The fluid velocity field distribution diagram of the inverted droplet “Marangoni convection + natural convection” is (f); Figure 5 The fluid velocity field distribution diagram of the inverted droplet “Marangoni convection” is (g); Figure 5 The fluid velocity field distribution diagram of the inverted droplet “natural convection” is (h).

[0108] To explore the difference of the flow field in the evaporation process of the upright droplet and the inverted droplet, the present application uses the simulation software COMSOL to carry out simulation, and the simulation results are as shown in Figure 5 Figure 6 ​It can be seen that the flow inside the droplet is the result of the combined action of Marangoni flow, natural convection and capillary flow. After the hydrophobic treatment of the silicon wafer substrate, the capillary flow in the droplet flow is inhibited. Therefore, the present application mainly considers the interaction of Marangoni flow and natural convection. For this purpose, the present application establishes three models, namely the "Marangoni flow + natural convection" model (σT=1×10 -6 N / (m·K), g=9.8 m / s 2 ); "Marangoni flow" model (σT=1×10 -6 N / (m·K), g=0 m / s 2 , without the natural convection term); "natural convection" model (σT=0 N / (m·K), g=9.8 m / s 2 , without the Marangoni flow term). The present application finds that the temperature profiles simulated by the two single convection modes ( Figure 5 ) are highly similar to the temperature profiles simulated by the "Marangoni + natural convection" mode ( Figure 5 (a)) in both the sitting droplet and the pendant droplet, and are curvedly distributed, which indicates that the isopycnic surface also has a certain degree of bending. Figure 5 (c) and Figure 5 (d) are the "Marangoni flow" fluid velocity field distribution diagrams of the upright droplet and the inverted droplet, respectively, and it can be found that the flow fields of the two are opposite, and the Marangoni flow velocity of the inverted droplet is larger, being 6.81 μm / s. Corresponding to the "Marangoni flow" fluid velocity field distribution diagrams ( Figure 5 (d) and Figure 5 (h)), it can be observed that the overall flow field velocity of the two is small, being about 1.25 μm / s or so. However, the direction is different from the "Marangoni flow" field. For the upright droplet, the directions of the "natural convection field" and the "Marangoni flow" are opposite; for the inverted droplet, the directions of the "natural convection field" and the "Marangoni flow" are the same. The reaction is reflected in the final results, as shown in Figure 5 (b) and Figure 6 (f), it can be seen that the maximum velocity field of the upright droplet is 5.04 μm / s; the maximum velocity field of the inverted droplet is 7.04 μm / s.

[0109] Figure 6 are the temperature field simulation results of the "natural convection field" model and the "Marangoni flow field" model. Figure 6 (a) is the temperature field simulation result diagram of the "natural convection field" model of the upright droplet; Figure 6 (b) is the temperature field simulation result diagram of the "Marangoni flow field" model of the upright droplet; Figure 6 (c) is the temperature field simulation result diagram of the "natural convection field" model of the inverted droplet; Figure 12(d) is the inverted droplet "Marangoni flow field" model temperature field simulation results figure.

[0110] For the upright droplet, the "Marangoni flow" and "natural convection field" are considered jointly, and the directions of the two are opposite, and they weaken each other, which makes the fluid velocity field in the central region weaken, and therefore, the nanoparticles are more inclined to diffuse outward. Similarly, for the inverted droplet, the "Marangoni flow" and "natural convection field" are considered jointly, and the directions of the two are the same, and they enhance each other, which makes the fluid velocity field in the central region enhance. Therefore, the nanoparticles are more inclined to concentrate in the middle. In the case of mutual enhancement of Marangoni and natural convection, the nanoparticles cannot reach the edge of the pendant droplet, but are forced to return to the center of the droplet from the edge area by the stronger combined flow of Marangoni and natural convection. This change in flow field strongly reduces the pinning of the contact line, thereby allowing the nanoparticles to be transported to the center of the pendant droplet, which provides theoretical support for explaining that the microdome formed by the evaporation self-assembly after inversion has a higher H / D value.

[0111] Figure 12 After the three different particle sizes of PS-COOH nanospheres prepared in the present application 1 are prepared into the colloidal photonic crystal ink prepared in the example 4, different sizes of droplets (diameter of 200-600 μm) are jet-printed according to the printing method of the example 4, and it is found that the structural color brightness and saturation of the structure treated by the present application are improved, as shown in Figure 12 (a)-(c) in the figure are the structural color results of the PS-COOH sample 1 (169 nm) prepared in the example 1, as shown in Figure 12 (d)-(f) in the figure are the structural color results of the PS-COOH sample 2 (215 nm) prepared in the example 1, as shown in Figure 12 (g)-(i) in the figure are the structural color results of the PS-COOH sample 3 (252 nm) prepared in the example 1. As shown in Figure 12 (j)-(l) in the figure are the structural color comparison results of the PS-COOH sample 1, sample 2 and sample 3 prepared in the example 1. Among them, Figure 12 In (a), (d) and (g), I and IV correspond to the droplet diameter of 300 μm, II and V correspond to the droplet diameter of 400 μm, and III and VI correspond to the droplet diameter of 600 μm. Note: Figure 12 The sizes marked in (a), (d) and (g) are the diameters of the dried colloidal photonic crystal microdome, and the actual droplet diameter is about 10 times the size of the structure. Figure 12 In the figure, "sessiledrop" means the product formed by upright drying, and "pendant drop" means the product formed by inverted drying.

[0112] FromFigure 14 It is shown that the method provided by the present application is not for one particle size and one droplet size, but for a range of particle sizes and droplet sizes, and is proved to be effective.

[0113] Figure 14 Particle image velocimetry (PIV) results of the upright droplet and the inverted droplet in Example 4 of the present application. ​ It can be found by color contrast that the particle motion speed of the inverted droplet is faster, which is consistent with the simulation results described above.

[0114] From the above examples, it can be seen that the present application simplifies the complex electrohydrodynamic inkjet printing parameter and ink parameter adjustment process by a simple approximation method, and quickly finds the corresponding printable area. By adjusting the proportion of ethylene glycol continuous phase, the viscosity and surface tension of the colloidal photonic crystal ink are adjusted, the colloidal photonic crystal structure color micro-dome unit is successfully printed and evaporative self-assembly is formed. At the same time, by simply turning over the substrate for evaporative self-assembly, the brightness of the colloidal photonic crystal structure color is improved by 15% to 20%, and the saturation of the structural color is also improved.

[0115] Although the above examples have made a detailed description of the present application, it is only a part of the embodiments of the present application, but not all the embodiments, and other embodiments can be obtained according to the present embodiments without creativity, which all belong to the protection scope of the present application.

Claims

1. A method for preparing a colloidal photonic crystal structure color, characterized by, Includes the following steps: A patterned substrate is obtained by printing droplets on a substrate surface using colloidal photonic crystal ink, whereby the droplets form a patterned surface on the substrate. The colloidal photonic crystal ink comprises carboxylated polystyrene nanospheres, water, and ethylene glycol. The volume ratio of ethylene glycol to water is 7:

3. The mass concentration of the carboxylated polystyrene nanospheres in the colloidal photonic crystal ink is 0.03 g / mL. The patterned substrate is flipped 180° so that the patterned surface is upside down and evaporation self-assembly is performed to form colloidal photonic crystal structure color micro dome units on the substrate surface, thus obtaining colloidal photonic crystal structure color on the substrate surface.

2. The production method according to claim 1, characterized by, The carboxylated polystyrene nanospheres have a particle size of 169~252 nm, a hydration radius of 190~295 nm, and a PDI ≤ 0.

05.

3. The production method according to claim 1 or 2, characterized by, The preparation method of the carboxylated polystyrene nanospheres includes the following steps: In a protective gas atmosphere, water, α-methacrylic acid, sodium linear alkylbenzene sulfonate, sodium bicarbonate, styrene monomer, and potassium persulfate were mixed and reacted to obtain the carboxylated polystyrene nanospheres; the volume ratio of α-methacrylic acid to styrene monomer was 0.1:5.

5. The reaction was carried out at a temperature of 70°C for 8 hours.

4. The method of claim 1, wherein, The patterned printing is performed using the dot pattern mode of an electrohydraulic inkjet printer, with each droplet having a diameter of 200~600 μm.

5. The preparation method according to claim 4, characterized in that, The conditions for pattern printing by the electrohydrodynamic inkjet printer include: a duty cycle of 50%, a bias voltage of 800V, an amplitude of 800V, and a frequency of 200Hz.

6. The method of claim 1, wherein, The temperature for the evaporative self-assembly is 30°C and the relative humidity is 60%.

7. The preparation method according to claim 1, characterized in that, The substrate is a silicon wafer; prior to the patterning printing, the substrate is further subjected to hydrophobic treatment, which includes the following steps: plasma treatment of the substrate with oxygen to obtain a plasma-treated substrate; The plasma-treated substrate is hydrophobically treated with a hydrophobic treatment agent, which includes organic solvents and silane reagents.

8. The colloidal photonic crystal structure color prepared by the preparation method according to any one of claims 1-7, characterized in that, The colloidal photonic crystal structure color is composed of microdome units.

9. The colloidal photonic crystal structural color according to claim 8, wherein The height-to-diameter ratio of the microdome unit is 0.35, and the bottom diameter of the microdome unit is 20~40 μm.

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