Interfacial behavior of particles in nonpolar media: unveiling voltage-induced white state reduction and post-power-off enhancement in electrophoretic display

Electrophoretic display (EPD), a type of reflective display technology, is widely recognized for its advantages of bistability, low power consumption, and high ambient ratio. The operation of EPD relies on charged color particles migrating from one electrode interface to another under an electric field in a nonpolar medium. Therefore, the display performance is closely linked to the interfacial behavior of particles. However, the underlying mechanisms remain poorly understood. This study reveals two anomalous phenomena observed in EPD with aerosol OT (AOT) as surfactant: a decrease in white state under high driving voltages above a few tens of volts and an unexpected increase in white state after power removal. Through particle optical observation and tracking, we elucidate the interface behavior of particles behind these phenomena in AOT-modulated EPD. In the first case, particles bounce at the electrode due to particle polarity reversal at high voltage. In the second case, after the electric field is removed, particles move toward the electrodes due to a reduction in Coulomb repulsion and steric hindrance. Further, we propose the underlying mechanisms of these interface behaviors. The insights gained from this work offer valuable guidance for optimizing EPD performance, including bistability, contrast ratio, and ghosting effects.