(80f) Fabrication of Modified SiO2/ Benzidine Yellow Pigment Composite Particles for Electrophoretic Display

Electrophoretic display (EPD), which showing images and texts using moving charged particles under applied voltage, has attracted a great deal of interest because of their merits of good brightness and contrast, wide viewing angles, state bistability and low power consumption. To offer electrophoretic behavior in the EPD, it is required that differently charged pigment particles with different color were dispersed in the suspending medium. Organic pigments have brilliant color but poor solvent resistance. The pigment particles should be modified for electrophoretic display. SiO2/benzidine yellow pigment composite particles were fabricated by an electrostatic self-assembly method, using SiO2 as shell and benzidine yellow G (C. I. Pigment Yellow 12) or benzidine yellow GR (C. I. Pigment Yellow 13) as core. During the process of hydrolysis of Na2SiO3, a thin and compact shell of SiO2 was applied to coat the yellow pigment particles to enhance the optical and solvent resistance properties. In order to get good charging and electrophoresis properties of particles in dispersion medium, further surface modification is carried out. The coated particles were modified with 3-aminopropyltriethoxysilane (KH550) to give positive charged composite particles, and the coated particles were aslo modified with succinic acid to give negative charged composite particles. The obtained modified SiO2/benzidine yellow pigment composite particles were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared analysis (FT-IR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The particles were dispersed in tetrachloroethylene with hyperdispersants. Particle size distribution and zeta potential were measured by Beckman Coulter Delsa Nano zeta potential and submicron particle size analyzer. The above composite particles were dispersed in tetrachloroethylene first, then by in situ polymerization technology and complex coacervation method respectively, poly(urea-formaldehyde) microcapsules and gelatin-gum acacia microcapsules were prepared. And it was shown that the composite particles in the microcapsules had a reversible electric response in the electric field.