Preparation method of electrophoresis white particles based on atomic layer deposition and product thereof

Abstract

The invention provides a preparation method of electrophoresis white particles based on atomic layer deposition, which comprises the following steps: carrying out corrosive pretreatment on hollow glass microspheres in an alkaline solution to obtain a microsphere template; putting the microsphere template into a reactor, and sequentially and alternately introducing a titanium-based precursor and an oxygen-based precursor into the reactor under the purging of inert gas by utilizing an ALD (Atomic Layer Deposition) process, so as to obtain a titanium dioxide coated microsphere; and adding the titanium dioxide coated microspheres into a deionized water solution containing a surfactant for ultrasonic dispersion, and filtering and drying to obtain the electrophoresis white particles. High uniformity of particle size distribution, coating layer thickness and surface charge distribution is realized, uniform stress and consistent migration speed of particles in an electric field are ensured, the problems of smear, uneven brightness and the like in display application are effectively avoided, meanwhile, the stability of electrophoretic particles in the storage and use process is remarkably improved, and the display effect is improved. And the consistency and reliability of the product performance are ensured.

Description

Technical Field

[0001] This invention relates to the field of electrophoretic particle technology, specifically to a method for preparing electrophoretic white particles based on atomic layer deposition and the product thereof. Background Technology

[0002] As a core technology in the field of flexible, low-power displays, electronic paper's display performance directly depends on the motion response characteristics of electrophoretic particles within microcapsule or microcup structures. As the core carrier of light modulation, the precise control of the migration speed, orientation accuracy, stability, and uniformity of electrophoretic particles is a crucial prerequisite for determining the display quality, lifespan, and application expansion of electronic paper. The core display principle of electronic paper involves driving electrophoretic particles to migrate in a dispersed medium using an electric field, achieving pixel-level switching or color rendering. Precise control is essential to ensuring the stability and efficiency of this process.

[0003] The electronic paper industry is currently facing technological iteration demands for "high resolution, high refresh rate, low cost, and long lifespan," and precise control of electrophoretic particles is a key breakthrough to overcome industry bottlenecks. From a technological iteration perspective, high-resolution displays require continuous miniaturization of microcapsule / microcup structures, necessitating smaller particle sizes and higher uniformity (coefficient of variation below 5%). Only through precise control of particle synthesis processes and surface modification techniques can the controllability of movement at the micro-nano scale be achieved. Traditional electrophoretic particle preparation methods, centered on chemical synthesis (such as emulsion polymerization and dispersion polymerization) and physical coating (such as mechanical grinding and surface modification), produce electrophoretic particles with poor performance uniformity: particle size and surface charge density are prone to fluctuations (coefficient of variation often exceeding 10%), leading to asynchronous movement under an electric field, causing display ghosting and uneven brightness. Furthermore, due to the low precision of the surface coating layer thickness (deviation > 10nm) and insufficient density, long-term use easily leads to particle aggregation and charge decay, affecting the lifespan of electronic paper. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing electrophoretic white particles based on atomic layer deposition, comprising: Hollow glass microspheres were subjected to a corrosive pretreatment in an alkaline solution to obtain a microsphere template; The microsphere template was placed in the reactor, and the titanium-based precursor and the oxygen-based precursor were alternately introduced into the reactor under inert gas purging using the ALD process to obtain titanium dioxide-coated microspheres. Titanium dioxide-coated microspheres were added to a deionized aqueous solution containing a surfactant and ultrasonically dispersed. After filtration and drying, electrophoretic white particles were obtained.

[0005] Furthermore, the specific method for pretreating the hollow glass microspheres in an alkaline solution is as follows: The SiO2 on the surface of the hollow glass microspheres undergoes an etching reaction: SiO2 + 2OH- - →SiO3 2- +H₂O, after the etching reaction, hydroxyl groups are generated on the surface of the hollow glass microspheres. The lone pair electrons of the O atom in the hydroxyl group can react with the electron-deficient Ti atom in the titanium-based precursor (such as TiCl₄). 4+ Coordination bonds are formed, providing unique and stable chemically active sites for the adsorption of titanium-based precursors in the subsequent ALD process, preventing irregular deposition of precursors on the microsphere surface. After the etching reaction, hydroxyl groups formed on the microsphere surface are covalently bonded to titanium-based groups, ensuring a strong bond between the subsequently formed titanium dioxide coating layer and the hollow glass microsphere substrate, preventing coating detachment during use. The etching reaction removes trace impurities from the microsphere surface and uniformly generates hydroxyl groups, ensuring precursor adsorption on the microsphere surface in each ALD cycle, laying the foundation for particle size uniformity.

[0006] Furthermore, the specific method for sequentially and alternately introducing the titanium-based precursor and the oxygen-based precursor into the reactor under inert gas purging using the ALD process is as follows: First, the titanium-based precursor is blown toward the microsphere template under an inert gas purging, so that the hydroxyl groups on the surface of the microsphere template undergo a coordination adsorption reaction with the titanium-based precursor. At this time, the surface of the microsphere template is covered with a layer of titanium-based groups, and Ti atoms are covalently connected to the surface of the microsphere template through O atoms. The oxygen precursor is then blown onto the microsphere template under an inert gas purging, causing the titanium-based groups on the surface of the microsphere template to undergo a nucleophilic substitution reaction with the oxygen precursor, generating a single-atom layer of titanium dioxide, and hydroxyl groups are generated on the surface of the titanium dioxide layer.

[0007] The number of hydroxyl groups on the microsphere surface is fixed. After all hydroxyl groups combine with the titanium-based precursor, excess precursor cannot be adsorbed, ensuring that only a single layer of titanium-based groups (such as -O-TiCl3) is formed in each cycle, avoiding local over-thickness. The fixed number of titanium-based groups can only react with a quantitative amount of oxygen-based precursor to form a single atomic layer of titanium dioxide. Ultimately, atomic-level control of the coating thickness is achieved through multiple cycles. Both reactions are carried out layer by layer on the surface of the microsphere. Inert gas purging further avoids gas-phase reactions of the precursor, resulting in no gas-phase nucleation. The formed titanium dioxide layer is almost pinhole-free and has a packing density close to that of a blocky material, effectively blocking the erosion of the microsphere core by the dispersion medium. After the reaction, the titanium dioxide layer surface regenerates hydroxyl groups, which can serve as new active sites for the next ALD cycle. This allows the coating thickness to be flexibly adjusted by the number of cycles to adapt to different reflectivity and particle size requirements.

[0008] Furthermore, the concentration of hydroxide ions in the alkaline solution is ≥2 mol / L. The alkaline solution is any one of sodium hydroxide, potassium hydroxide, lithium hydroxide, and calcium hydroxide. -It is the core reactant for SiO2 etching. A concentration of ≥2mol / L can ensure that SiO2 on the surface of the microspheres reacts fully and generates a sufficient amount of hydroxyl groups. If the concentration is too low, the etching will be incomplete and the number of hydroxyl groups will be insufficient, which will lead to the absence of active sites during subsequent ALD deposition, resulting in problems such as discontinuous coating and local exposure.

[0009] Furthermore, in the ALD process, the reaction temperature is 120℃~200℃. This ensures that the titanium-based precursor (such as TiCl4, TTIP) has sufficient activity to rapidly coordinate and adsorb with the hydroxyl groups on the microsphere surface, while simultaneously ensuring that the oxygen-based precursor (such as H2O, O3) can efficiently participate in the nucleophilic substitution reaction. This avoids a slow reaction rate that would lead to a loose coating layer, and also prevents the hollow glass microspheres from softening, deforming, or collapsing due to high temperatures. Additionally, it prevents the titanium-based precursor from decomposing at high temperatures and generating impurities, thus ensuring the purity of the titanium dioxide coating layer.

[0010] Furthermore, in the ALD process, the titanium-based precursor and the oxygen-based precursor are alternately introduced into the reactor under inert gas purging for 5 to 300 cycles. If the number of cycles is less than 5, the coating layer is too thin, easily resulting in pinholes and failing to effectively block the dispersion medium, leading to a decrease in reflectivity. If the number of cycles is greater than 200, the coating layer is too thick, causing the particle size to be too large, resulting in slower electrophoretic migration and ghosting during display.

[0011] Furthermore, the surfactant is any one of KH550, KH560, KH570, SDS, LAS, CTAB, Triton X-100, Tween, and Span. The surfactant can significantly increase the absolute value of the zeta potential by modifying the particle surface charge, enhancing the electrostatic repulsion between particles, effectively inhibiting aggregation and sedimentation, and extending the storage period of the electrophoresis solution. After surfactant modification, the particles are more uniformly dispersed, experience consistent forces in the electric field, have stable migration speeds, and shorten the response time for display and separation applications.

[0012] Furthermore, the titanium-based precursor is any one of TiCl4, TTIP, and TDMAT.

[0013] Furthermore, the oxygen precursor is any one of H2O, O2, O3 and H2O2.

[0014] The electrophoretic white particles prepared according to the method of preparing electrophoretic white particles based on atomic layer deposition have a reflectivity of 27% to 31% for the titanium dioxide layer and a particle size of 150 to 320 nm for the electrophoretic white particles.

[0015] Furthermore, the hollow glass microspheres have a diameter of 50-300 nm.

[0016] The beneficial effects of this invention are as follows: 1. Leveraging the unique self-limiting surface reaction characteristics of the ALD process, each round of precursor introduction results in a single-atom-thick titanium dioxide deposition layer on the surface of the microsphere template. By precisely controlling the number of reaction cycles from 5 to 300, the thickness of the coating layer can be precisely controlled at the atomic level. This precise control mechanism not only strictly controls the particle size of the electrophoretic white particles within the range of 150-320 nm, but also achieves high uniformity in particle size distribution, coating layer thickness, and surface charge distribution. This ensures that the particles experience uniform force and consistent migration speed in the electric field, effectively avoiding problems such as ghosting and uneven brightness in display applications. Simultaneously, it significantly improves the stability of the electrophoretic particles during storage and use, ensuring the consistency and reliability of product performance.

[0017] 2. Compared to traditional emulsion polymerization, dispersion polymerization, and physical coating methods, the titanium dioxide coating layer constructed by the ALD process in this invention has a nearly pinhole-free dense structure with a packing density close to that of bulk materials, fundamentally solving the technical pain point of high porosity in traditional coating layers. The dense coating layer can firmly lock in surface charge groups, preventing their loss due to pores; simultaneously, it can effectively block the erosion of the microsphere core by the dispersion medium, preventing particle performance degradation, thereby completely avoiding the occurrence of undesirable phenomena such as image retention, dark spots, and bright spots in display scenarios, significantly extending the service life of electrophoretic display devices, and improving the long-term stability of the product.

[0018] 3. The entire preparation process of this invention uses deionized water, alkaline aqueous solutions (sodium hydroxide, potassium hydroxide, etc.), and inert gases as reaction media and purge gases, without using any toxic organic solvents, thus eliminating the risk of environmental pollution at the source. Furthermore, the self-limiting deposition characteristics of the ALD process ensure uniform and complete coverage of the titanium dioxide coating, resulting in a narrow particle size distribution and high purity of the product. No additional sorting, purification, or other subsequent processing steps are required, simplifying the production process, reducing production costs, and avoiding secondary pollution. The entire preparation process exhibits good compatibility with biological and ecological environments, aligning with the concept of green development. Attached Figure Description

[0019] Figure 1 The infrared spectrum of the electrophoretic white particles prepared in Example 1.

[0020] Figure 2 This is a transmission electron microscope image of the electrophoretic white particles prepared in Example 1. Detailed Implementation

[0021] Unless otherwise specified, all raw materials used below are commercially available products, and all methods used below are conventional methods in this field.

[0022] The full names of the abbreviations used in this invention are as follows: TTIP: Titanium isopropoxide; TDMAT: Tetra-(dimethylaminotitanium); KH550: γ-aminopropyltriethoxysilane; KH560: γ-glycidyl etheroxypropyltrimethoxysilane; KH570: γ-methacryloyloxypropyltrimethoxysilane; SDS: Sodium dodecyl sulfate; LAS: Sodium dodecylbenzenesulfonate; CTAB: Hexadecyltrimethylammonium bromide; Triton X-100: Polyethylene glycol octylphenyl ether; Tween: Tween derivatives; Span: Span trisorbitan fatty acid esters.

[0023] ALD (Atomic Layer Deposition) is a vapor-phase thin film deposition technology based on self-limiting surface reactions. Its core principle involves alternately and pulsedly introducing two or more gaseous precursors, causing the precursors to undergo layer-by-layer, self-limiting chemical reactions on the substrate surface, ultimately depositing a thin film of uniform thickness and controllable composition, with film thickness accurate to the atomic layer level.

[0024] Example 1 Take 20g of hollow glass microspheres and add them to a round-bottom flask containing 150mL of sodium hydroxide solution with a concentration of 3mol / L. Heat the flask to 60℃ and disperse it by mechanical stirring for 8 hours. After washing and centrifugation several times, and after the washing liquid is neutral, dry the solid to obtain the microsphere template that has undergone corrosion pretreatment. Based on the principle of atomic layer deposition, the titanium-based precursor TiCl4 and the oxygen-based precursor H2O were alternately introduced into the reactor under high-purity nitrogen purging. The reaction temperature in the chamber was 150℃. After 200 cycles of reaction, the generated titanium dioxide was uniformly coated on the surface of the microsphere template that had undergone corrosion pretreatment, resulting in titanium dioxide-coated microspheres. The titanium dioxide-coated microspheres were added to a deionized aqueous solution containing 5 wt% KH570 and ultrasonically dispersed at 50°C for 2 h for modification. After filtration and drying, electrophoretic white particles were obtained.

[0025] Figure 1 and Figure 2 The images show the infrared spectrum and transmission electron microscopy results of the electrophoretic white particles prepared in Example 1. Figure 1 The peaks in the middle are assigned as follows: 3452cm -1 The peak at 2935 cm⁻¹ is the stretching vibration peak of -OH on the surface of KH570 modified glass microspheres-titanium dioxide, possibly due to a small amount of water absorption on the titanium dioxide surface; -1 and 2842cm -1 The peaks at 2336 cm⁻¹ correspond to the asymmetric and symmetric stretching vibration peaks of -CH₂-, respectively. -1 The peak at 1739 cm⁻¹ is a characteristic peak of the carbonyl group (C=O). -1 With 1613cm-1 Unsaturated carbon (-C=C-) belonging to KH570, 1143 cm -1 The peak at 628 cm⁻¹ corresponds to the Si-OC bond. -1 The peak at that location is attributed to the stretching vibration peak of Ti-O. Figure 2 The prepared electrophoretic white particles show that they have a relatively regular shape and uniform particle size. The above analysis confirms that the KH570 modified glass microspheres-titanium dioxide electrophoretic white particles in Example 1 have been successfully prepared.

[0026] First, the Ti in the TiCl4 molecule 4+ As an electron-deficient center, TiCl4 can form coordinate bonds with the lone pair electrons of the O atoms in the -OH group on the microsphere template surface, achieving chemisorption. The number of -OH active sites on the microsphere template surface is fixed. Once all -OH groups have bound to TiCl4, there are no more adsorbable active sites on the surface, and excess TiCl4 cannot be adsorbed. This process ensures that each TiCl4 pulse forms only a single layer of Ti-Cl bonded coating on the microsphere surface, with uniform and controllable thickness. The reaction equation is as follows: -OH + TiCl4 → -O-TiCl3 + HCl↑. At this point, the microsphere template surface is covered with a layer of -O-TiCl3 groups, and the Ti atoms are covalently connected to the microsphere template surface through O atoms. Next, the O atoms in the H2O molecule are electron-rich centers and can attack the Ti atoms in the -O-TiCl3 groups. 4+ The -O-TiCl3 group on the surface of the microsphere template replaces the terminal Cl atoms, while the H atoms in H2O combine with the Cl atoms to generate HCl byproducts. The number of -O-TiCl3 groups on the surface of the microsphere template is fixed. When all Cl atoms are replaced by O atoms in H2O, the reaction automatically stops. This process ensures that each H2O pulse only converts the Ti-Cl layer on the surface into a TiO2 monolayer with a thickness ≤0.1nm (corresponding to the atomic layer thickness of TiO2). The initial reaction is as follows: surface -Si-O-TiCl3 + 3H2O → surface -Si-O-Ti(OH)3 + 3HCl↑. Subsequently, the -OH in the surface Ti(OH)3 undergoes dehydration condensation: surface -O-Ti(OH)3 → surface -O-TiO 1.5 +1.5H₂O↑ (The basic structural unit TiO₂ is ultimately formed) 1.5 After multiple cycles, a complete TiO2 crystal structure is formed. At this point, the surface of the microsphere template is in the following state: a dense TiO2 single-atom layer is generated, Ti atoms are connected to the surface of the microsphere template through O atoms, and new hydroxyl groups (-OH) are re-exposed on the surface of the TiO2 layer. These newly generated -OH groups serve as new active sites for TiCl4 adsorption in the next ALD cycle, laying the foundation for subsequent deposition.

[0027] After one ALD cycle, high-purity N2 or Ar or other inert gases are introduced to completely remove TiCl4 that has not combined with the surface -OH groups. This prevents TiCl4 from reacting directly with H2O in the gas phase to form TiO2 particles when oxygen precursors are introduced later. If TiCl4 remains, it will cause nucleation in the gas phase, forming free TiO2 impurities and disrupting the uniformity of the coating layer. The HCl generated in the reaction is discharged with the inert gas to prevent HCl residue from corroding the microsphere surface or affecting subsequent reactions. After each reaction step, the system is thoroughly purged to ensure that adjacent precursors do not come into direct contact and that the reaction occurs only on the surface of the microsphere template.

[0028] Example 2 Take 20g of hollow glass microspheres and add them to a round-bottom flask containing 150mL of sodium hydroxide solution with a concentration of 3mol / L. Heat the flask to 60℃ and disperse it by mechanical stirring for 8 hours. After washing and centrifugation several times, and after the washing liquid is neutral, dry the solid to obtain the microsphere template that has undergone corrosion pretreatment. Based on the principle of atomic layer deposition, the titanium-based precursor TTIP and the oxygen-based precursor H2O were alternately introduced into the reactor under high-purity nitrogen purging. The reaction temperature in the chamber was 150℃. After 200 cycles of reaction, the generated titanium dioxide was uniformly coated on the surface of the microsphere template that had undergone corrosion pretreatment, resulting in titanium dioxide-coated microspheres. The titanium dioxide-coated microspheres were added to a deionized aqueous solution containing 5 wt% KH570 and ultrasonically dispersed at 50°C for 2 h for modification. After filtration and drying, electrophoretic white particles were obtained.

[0029] Example 3 Take 20g of hollow glass microspheres and add them to a round-bottom flask containing 150mL of sodium hydroxide solution with a concentration of 3mol / L. Heat the flask to 60℃ and disperse it by mechanical stirring for 8 hours. After washing and centrifugation several times, and after the washing liquid is neutral, dry the solid to obtain the microsphere template that has undergone corrosion pretreatment. Based on the principle of atomic layer deposition, the titanium-based precursor TiCl4 and the oxygen-based precursor H2O2 were alternately introduced into the reactor under high-purity nitrogen purging. The reaction temperature in the chamber was 150℃. After 200 cycles of reaction, the generated titanium dioxide was uniformly coated on the surface of the microsphere template that had undergone corrosion pretreatment, resulting in titanium dioxide-coated microspheres. The titanium dioxide-coated microspheres were added to a deionized aqueous solution containing 5 wt% KH570 and ultrasonically dispersed at 50°C for 2 h for modification. After filtration and drying, electrophoretic white particles were obtained.

[0030] Example 4 Take 20g of hollow glass microspheres and add them to a round-bottom flask containing 150mL of sodium hydroxide solution with a concentration of 3mol / L. Heat the flask to 60℃ and disperse it by mechanical stirring for 8 hours. After washing and centrifugation several times, and after the washing liquid is neutral, dry the solid to obtain the microsphere template that has undergone corrosion pretreatment. Based on the principle of atomic layer deposition, the titanium-based precursor TiCl4 and the oxygen-based precursor H2O were alternately introduced into the reactor under high-purity nitrogen purging. The reaction temperature in the chamber was 150℃. After 200 cycles of reaction, the generated titanium dioxide was uniformly coated on the surface of the microsphere template that had undergone corrosion pretreatment, resulting in titanium dioxide-coated microspheres. The titanium dioxide-coated microspheres were added to a deionized aqueous solution containing 5 wt% CTAB and ultrasonically dispersed at 50°C for 2 h for modification. After filtration and drying, electrophoretic white particles were obtained.

[0031] Example 5 Take 20g of hollow glass microspheres and add them to a round-bottom flask containing 150mL of sodium hydroxide solution with a concentration of 3mol / L. Heat the flask to 60℃ and disperse it by mechanical stirring for 8 hours. After washing and centrifugation several times, and after the washing liquid is neutral, dry the solid to obtain the microsphere template that has undergone corrosion pretreatment. Based on the principle of atomic layer deposition, the titanium-based precursor TTIP and the oxygen-based precursor H2O were alternately introduced into the reactor under high-purity nitrogen purging. The reaction temperature in the chamber was 150℃. After 200 cycles of reaction, the generated titanium dioxide was uniformly coated on the surface of the microsphere template that had undergone corrosion pretreatment, resulting in titanium dioxide-coated microspheres. The titanium dioxide-coated microspheres were added to a deionized aqueous solution containing 5 wt% CTAB and ultrasonically dispersed at 50°C for 2 h for modification. After filtration and drying, electrophoretic white particles were obtained.

[0032] Example 6 Take 20g of hollow glass microspheres and add them to a round-bottom flask containing 150mL of sodium hydroxide solution with a concentration of 3mol / L. Heat the flask to 60℃ and disperse it by mechanical stirring for 8 hours. After washing and centrifugation several times, and after the washing liquid is neutral, dry the solid to obtain the microsphere template that has undergone corrosion pretreatment. Based on the principle of atomic layer deposition, the titanium-based precursor TTIP and the oxygen-based precursor H2O were alternately introduced into the reactor under high-purity nitrogen purging. The reaction temperature in the chamber was 150℃. After 200 cycles of reaction, the generated titanium dioxide was uniformly coated on the surface of the microsphere template that had undergone corrosion pretreatment, resulting in titanium dioxide-coated microspheres. The titanium dioxide-coated microspheres were added to a deionized aqueous solution containing 5 wt% Span85 (sorbitan trioleate) and ultrasonically dispersed at 50°C for 2 h for modification. After filtration and drying, electrophoretic white particles were obtained.

[0033] Comparative Example 1 Take 20g of hollow glass microspheres and add them to a round-bottom flask containing 150mL of sodium hydroxide solution with a concentration of 3mol / L. Heat the flask to 60℃ and disperse it by mechanical stirring for 8 hours. After washing and centrifugation several times, and after the washing liquid is neutral, dry the solid to obtain the microsphere template that has undergone corrosion pretreatment. Based on the principle of atomic layer deposition, the precursor TiCl4 and precursor H2O are alternately introduced into the reactor under high-purity nitrogen purging. The reaction temperature in the chamber is 150℃. After 200 cycles of reaction, the generated titanium dioxide is uniformly coated on the microsphere template that has undergone corrosion pretreatment, thus obtaining electrophoretic white particles without surfactant modification.

[0034] Comparative Example 2 75 mL of anhydrous ethanol was placed in a 250 mL round-bottom flask, and 25 mL of tetrabutyl titanate was slowly added to obtain a pale yellow solution 1. Then, 35 mL of anhydrous ethanol, 10 mL of deionized water, and 2 mL of glacial acetic acid were measured and mixed thoroughly. Dilute hydrochloric acid was added dropwise until the pH reached 3, yielding solution 2. Under ice-water bath conditions, solution 2 was slowly added dropwise to solution 1 using a constant-pressure low-pressure funnel. After all solution 2 had been added, the temperature was adjusted to 40 °C, and the reaction was continued with slow stirring for 1 hour. The resulting gel-like substance was titanium dioxide gel. This gel was then calcined in a muffle furnace at 350 °C for 4.5 hours to obtain titanium dioxide particles prepared by the solution-gel method.

[0035] The TiO2 particles prepared by the solution-gel method were added to a deionized aqueous solution containing 5 wt% KH570 and ultrasonically dispersed at 50°C for 2 h for modification. After filtration and drying, the solution-gel method-prepared titanium dioxide electrophoretic white particles modified with KH570 were obtained.

[0036] (1) White-state reflectance test The reflectance of electrophoretic white particles was tested using a Nicolet IS50 Fourier transform infrared spectrometer (equipped with a Pike gold integrating sphere and an MCT liquid nitrogen detector) manufactured by Thermo Fisher Scientific, USA. Gold was used as the background, 128 scans were performed, and the scan parameter was reflectance with a resolution of 4.0. The results are shown in Table 1.

[0037] (2) Particle size and zeta potential test 0.03 g of white electrophoretic particles were added to 10 mL of isoparaffin and dispersed until uniform. The particle size distribution and zeta potential of the white electrophoretic particles were tested using a laser nanoparticle size and zeta potential analyzer. The results are shown in Table 1.

[0038] Table 1 Performance test results of Examples 1-6 and Comparative Examples 1-2 As shown in Table 1, compared with the titanium dioxide electrophoretic white particles prepared by the solution-gel method in Comparative Example 2, the electrophoretic white particles prepared by the ALD process in Examples 1-6 all exhibit higher white-state reflectivity. This is partly because the ALD process is based on surface self-limiting reaction layer-by-layer deposition, resulting in films with almost no pinholes and a packing density close to that of bulk materials. This reduces light scattering and loss within the film layer, avoiding the reflectivity decrease caused by film porosity and defects in traditional processes. Furthermore, ALD can achieve uniform full coverage of the microsphere template, ensuring that there are no weak reflective areas due to uneven local coating layers.

[0039] Compared to Comparative Example 1, the zeta potential (absolute value) of the electrophoretic white particles modified with surfactants was significantly increased, resulting in stronger electrostatic repulsion between particles. This helps prevent aggregation and sedimentation, thus extending the storage and usage period of the electrophoretic solution. Simultaneously, the stronger electrostatic driving force means that the particles respond faster in an electric field, which is beneficial for shortening response time in applications such as display and separation.

[0040] Furthermore, the electrophoretic white particles prepared using the ALD process in Examples 1-6 and Comparative Example 1 have smaller particle sizes and more uniform distributions, generally ranging from 150-320 nm. In contrast, the titanium dioxide electrophoretic white particles prepared using the solution-gel method have relatively larger particle sizes and a wider distribution. This uniform particle size distribution facilitates the uniform force exerted on the electrophoretic particles in the electric field, maintaining a consistent migration speed, avoiding ghosting during display, ensuring consistent brightness of the displayed image, and preventing delamination and aggregation, thus extending the system's lifespan.

[0041] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for preparing electrophoretic white particles based on atomic layer deposition, characterized by, The preparation method comprises the following steps: The hollow glass microspheres are subjected to a corrosive pretreatment in an alkaline solution to obtain a microsphere template; The microsphere template is placed into a reactor, and a titanium-based precursor and an oxygen-based precursor are alternately introduced into the reactor under inert gas purging by using an ALD process to obtain microspheres coated with titanium dioxide; The microspheres coated with titanium dioxide are ultrasonically dispersed in a deionized water solution containing a surfactant, and then filtered and dried to obtain electrophoretic white particles.

2. The method of claim 1, wherein the atomic layer deposition-based preparation of electrophoretic white particles is characterized by, The specific method for the corrosive pretreatment of the hollow glass microspheres in the alkaline solution is as follows: Etching reaction of SiO2 on the surface of hollow glass microspheres: SiO2+ 2OH - → SiO3 2- + H2O, and hydroxyl groups are generated on the surface of the hollow glass microspheres after the etching reaction.

3. The method of claim 1, wherein the atomic layer deposition-based preparation of electrophoretic white particles is characterized by, The specific method for the ALD process is as follows: First, the titanium-based precursor is blown to the microsphere template under inert gas purging, so that the hydroxyl groups on the surface of the microsphere template undergo a coordination adsorption reaction with the titanium-based precursor, and a layer of titanium-based groups is formed on the surface of the microsphere template, and the Ti atoms are covalently connected to the surface of the microsphere template through O atoms; Then, the oxygen-based precursor is blown to the microsphere template under inert gas purging, so that the titanium-based groups on the surface of the microsphere template undergo a nucleophilic substitution reaction with the oxygen-based precursor to form a monatomic layer of titanium dioxide, and hydroxyl groups are generated on the surface of the titanium dioxide layer.

4. The preparation method of the electrophoretic white particles based on atomic layer deposition according to claim 1, characterized in that: The concentration of hydroxyl ions in the alkaline solution is ≥ 2 mol / L.

5. The preparation method of the electrophoretic white particles based on atomic layer deposition according to claim 1, characterized in that: In the ALD process, the reaction temperature is 120-200°C.

6. The preparation method of the electrophoretic white particles based on atomic layer deposition according to claim 1, characterized in that: In the ALD process, the titanium-based precursor and the oxygen-based precursor are alternately introduced into the reactor under inert gas purging for 5-300 cycles.

7. The preparation method of the electrophoretic white particles based on atomic layer deposition according to claim 1, characterized in that: The surfactant is any one of KH550, KH560, KH570, SDS, LAS, CTAB, Triton X-100, Tween and Span.

8. The preparation method of the electrophoretic white particles based on atomic layer deposition according to claim 1, characterized in that: The titanium-based precursor is any one of TiCl4, TTIP and TDMAT.

9. The preparation method of the electrophoretic white particles based on atomic layer deposition according to claim 1, characterized in that: The oxygen-based precursor is any one of H2O, O2, O3 and H2O2.

10. The electrophoretic white particle prepared according to the method of any one of claims 1 to 9, characterized in that: The reflectivity of the titanium dioxide layer is 27-31%, and the particle size of the electrophoretic white particles is 150-320 nm.

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