Low-power structural-color electrophoretic display with high color purity via self-assembled charged colloidal arrays of PS@P(tBMA-co-BA) in a nonpolar medium.

We implement pigment-free full-color electrophoretic displays (EPDs) using a crystalline colloidal array (CCA) system composed of charged, monodisperse colloids uniformly dispersed in a nonpolar medium. The charge-stabilized CCA photonic inks consisted of PS@P(tBMA-co-BA) colloids dispersed in a designed isoparaffinic liquid. We hypothesized that the high-refractive-index PS core enhanced the structural color purity and incorporation of polar solvents improved the color tunability by enhancing particle charging. In the experiments, the surface of the PS@P(tBMA-co-BA) colloids was negatively charged via adsorption of charged reverse micelles enabling the formation of charge-stabilized CCAs. We find that a medium consisting of a mixture of n-hexanol and water maximizes the color tunability. Using PS@P(tBMA-co-BA) colloids of 175 nm and 210 nm in diameter, CCAs exhibiting structural color transitions from red to green and from green to blue, respectively, under an applied voltage of 4 V were successfully fabricated. EPD devices constructed with the photonic inks demonstrated low-power operation, with drive currents below 1.1 μA cm-2 at 4 V. Using the vivid structural colors achieved in the EPD system, a device employing two types of CCAs provided a color gamut covering 30% of the NTSC color space, demonstrating its potential for high-performance, pigment-free full-color display applications.