Preparation And Electrophoretic Properties Of Colored Inorganic Hollow Particles

Electrophoretic display technology,as a reflective display technology,offers several advantages,including low energy consumption,eye safety,and excellent visibility.Currently,black and white electrophoretic displays have been successfully commercialized,but they fail to meet the diverse needs of humanity,hence the urgent need to develop electrophoretic display technology for color displays.This display technology can achieve color display by controlling the electrophoresis speed method and sub-pixel method,but both methods require color electrophoresis particles with excellent electrophoresis performance.However,the organic pigment particles currently used have drawbacks such as irregular shape,poor light resistance,poor weather resistance,and high cost.Therefore,inorganic pigments with stable physical and chemical properties were selected as the coloration part of the electrophoretic particles,and hollow colored electrophoretic particles were prepared using the sacrificial template method.The hollow structure reduces the density difference between inorganic pigment and dielectric so that the gravity of electrophoretic particles is equal to the buoyancy;the particles prepared by the sacrificial template method have a regular spherical shape,which ensures uniform force distribution during the electrophoresis process;this improves the display speed and bistable display performance of electrophoretic particles.This paper successfully prepared blue（SiO₂-Co Al₂O₄）and green（SiO₂-Cr₂O₃）hollow electrophoretic particles with a double shell structure,and studied their electrophoretic properties in tetrachloroethylene.The main research content and results are as follows:（1）The size distribution,sphericity and surface morphology of template particles largely determine the electrophoretic performance of the hollow electrophoresis particles prepared later.In this theses,soap-free emulsion polymerization was used to prepare polystyrene（PS）microspheres,and then hydrolyzed tetraethyl orthosilicate（TEOS）was used to coat a layer of silicon dioxide（PS-SiO₂）on the surface of PS microspheres to prepare appropriate template particles.The influence of the modification time and amount of 3-aminopropyl triethoxysilane（APTES）,TEOS concentration,and alcohol-water ratio in the reaction system on the surface morphology of PS-SiO₂ particles was investigated.Experimental analysis revealed that PS-SiO₂particles with a smooth surface,uniform spherical shape,narrow size distribution;and an average particle size of approximately 250 nm were synthesized with 0.5 g polystyrene,0.1 g APTES,15 min modification time,0.6 m L TEOS,and a 6:1alcohol-water ratio in the reaction system.（2）The morphology,structure,and chromaticity of hollow structure electrophoretic particles have a significant impact on their motion speed and color rendering effect.In order to obtain color electrophoretic particles with excellent electrophoretic performance,core-shell structured PS-SiO₂ particles were employed as templates in this study for the synthesis of blue hollow particles using Al（NO₃）₃·9H₂O and Co（NO₃）₂·6H₂O as raw materials via a co-precipitation method.Further research was conducted on the effects of heating rate,calcination temperature,and raw material Co:Al ratio on particle chromaticity and hollow structure.The results show that when the heating rate is 1.5℃/min,the calcination temperature is 900℃,and the raw material Co:Al ratio is 0.8:2,the prepared SiO₂-Co Al₂O₄ particles have the best chromaticity,complete hollow structure,and smooth surface.Meanwhile,using Cr Cl₃·6H₂O as the main raw material,the effects of preparation methods,calcination temperature and coated metal oxide species on the chromaticity and morphology of green particles were studied.The results show that when the Pechini Sol-gel method is used,the calcination temperature is 900°C,and chromium trioxide（Cr₂O₃）is used as the coating layer,the prepared particles have the best chromaticity and smooth surface.The average diameters of blue and green particles measured by transmission electron microscopy are about 245 nm and 250 nm,respectively,and the thickness of the coating layer is about 18 nm and 15 nm,respectively.The CIE L^*a^*b^*values of blue particles measured by a colorimeter were 36.902,-11.360,and-13.974,respectively,while the CIE L^*a^*b^*values of green particles were 41.440,-11.910,and 9.766,respectively.（3）The electrophoretic performance of the prepared hollow electrophoretic particles was tested using a self-made electrophoretic display,and the prepared blue and green particles were mixed with the modified TiO₂ white particles respectively,to obtain the electrophoretic solution with blue-white and green-white display.The Zeta potential and electrophoretic mobility of modified TiO₂ particles are 15.5 m V and1.218×10^-8 m²·V^-1·s^-1,respectively.The Zeta potential and electrophoretic mobility of the prepared blue particles were-24.4 m V and-1.915×10^-8 m²·V^-1·s^-1,respectively.The Zeta potential and electrophoretic mobility of the green particles were-24.6 m V and-1.931×10^-8 m²·V^-1·s^-1.The response time of blue-white and green-white color development was measured by electrophoresis display to be around 300 ms,with fast color development speed and the ability to cycle color development.This indicates that the prepared hollow structured color electrophoretic particles have excellent electrophoretic performance,which provides practical basis for the subsequent development of high-performance color electrophoretic display technology.