Positively charged $TiO_2$ particles in non-polar system for electrophoretic display

Abstract

Electrophoretic display uses a technique called electrophoresis to represent images and letters electronically with electronic ink. Although it has good characteristics such as wide viewing angle, high contrast ratio and extremely low power consumption, there are still several issues to be resolved to improve its performances. Higher mobility and stability of the ink particles are the most important issues among them. In this study, $TiO_2$ particles coated with acrylamide were found to be effective ink particles that satisfy higher mobility and stability. The $TiO_2$ particles coated with 5~40% acrylamide were prepared by dispersion polymerization using monomers of methyl methacrylate (MMA) and acrylamide. The $TiO_2$ particles coated with acrylamide were dispersed in isopar-G with sorbitan esters such as span 20, span 80 and span 85. The size of the $TiO_2$ particles were changed from 200±150 nm to 350~500 nm by the coating process. The morphology of coated particles was observed using a transmission electron microscope (TEM) and thermogravimetric analysis (TGA). From the TGA results, the weight fraction of $TiO_2$ and polymer in coated particle were calculated. From the zeta potential measurement, it was shown that as acrylamide concentration was increased from 5% to 30%, zeta potential of the coated $TiO_2$ particles was increased from 50mV to about 230mV. The zeta potential of the coated $TiO_2$ particles with 40% acrylamide was decreased to 50mV. As a stabilizer, span 85 was the most effective surfactant to improve stability of the $TiO_2$ particles coated with acrylamide among used surfactants in this study. Span 85 showed best stability in the storage test with $TiO_2$ particles coated with 10% acrylamide. The mobility of $TiO_2$ particles coated with acrylamide with span 85 in dye solution (Oil Blue-N dissolved in isopar-G) were measured by ITO cell test. The mobility of $TiO_2$ particles coated with 10~30% acrylamide was over $600㎛^2/Vs$ while...