Adjusting the charging behavior of TiO₂ with basic surfactants in an apolar medium for electrophoretic displays

Electrophoretic displays (EPDs) are attracting attention as potential candidates for information display due to their eye-friendly nature, environmental friendliness and bistability. However, their response speed, which is closely related to the charging behavior of electrophoretic particles, is still inadequate for practical applications. Herein, five basic surfactants were employed to adjust the particle charge of titanium dioxide (TiO₂) in the apolar medium Isopar L. Particle charge is strongly related to the effective surfactant coverage on surface sites, dominated by the interaction between anchoring groups and solvation chains. As a result, the electrophoretic mobility of TiO₂ could be tuned between -8.09 × 10^-10 and +2.26 × 10^-10 m² V^-1 s^-1. Due to the increased particle charge, TiO₂ particles could be well dispersed in Isopar L with the assistance of S17000, T151 and T154. A black-white dual particle electrophoretic system with 2.0% (w/v) S17000 was constructed to obtain EPD devices. The EPD device gained a maximum white-and-black-state reflectivity of 41.79%/0.56% and a peak contrast ratio of 74.15. Its response time could be reduced to as low as 166.7 ms, which outperforms the majority of other black-white EPD devices.