Particle synthesis based on the concerted effect of mixed acid-base functional groups for electrophoretic display

The development of fast-response and full-color Electrophoretic Displays (EPDs) requires both rapid migration of electrophoretic particles and adjustable mobility of particles with different colors in apolar media, which is determined by the charged properties of the particle surface. Herein, five electrophoretic particles were synthesized with different ratios of acidic and basic functional groups to explore the impact of mixed functional groups on the effective pH of the particle surface. The prepared particles were characterized by FTIR, TGA and zeta potential measurements. The results show that the effective acidity of TiO2-NH2-COOH particles, which contain both acidic and basic functional groups, was higher than that of TiO2-COOH-COOH particles containing a single functional group. The surface charge of the electrophoretic particles increased from − 43 mV to − 90 mV. Similarly, TiO2-COOH-NH2 particles had a higher surface charge than TiO2-NH2-NH2 particles. The effective pH value of the particle surface depends on the synergism of mixed acid-base functional groups. The appropriate amounts of basic (or acidic) functional groups promote the acid-base interaction between acidic (or alkaline) functional groups and surfactant molecules, leading to an increase in the charge value of the particles. Thus, the effective acid-base of the particles can be precisely controlled by adjusting the mixing ratio of acid-base functional groups during particle modification. The application of electrophoretic particles with mixed acid-base functional groups was also demonstrated in two-color and three-color electrophoretic inks, achieving fast response (switching time decreased from 1170 ms to 130 ms) and colored display. This work may help to enhance the comprehension of the interaction mechanism between acid-base groups and particle-reverse micelle interfaces in non-polar solvents. Additionally, it may contribute to the precise modulation of the effective pH value on the particle surface, thereby facilitating the development of advanced functional materials.