The Preparation And Properties Of Dual-particle Electrophoretic Suspensions For Multicolor Electrophoretic Display

Electrophoretic displays (EPD) have been one of the most advantageous technology applied to E-paper because of its interesting features such as good contrast ratio, wide viewing angles, low power consumption, light-weight and flexibility. As the key materials for display, dual-particle electrophoretic suspensions are always a hot and difficult subject. The ideal electrophoretic suspensions should have the following properties, such as suspension stability, charging of the particles. Although the related products for EPD have been successfully commercialized under the promotion of E-ink Corporation, the types of specific materials and preparation methods are unclear in the open literatures. With the above considerations in mind, in this dissertation, a variety of composite particles were prepared by inorganic/organic composite method, the suspension stability and charging of the particles in the dispersion medium were emphatically studied, the preparation and properties of the dual-particle electrophoretic suspensions were discussed in detail, and then, the EPD prototype devices were fabricated, the device showed good optical properties and dynamic response when driven at low voltage. The works are listed as follows:TiO2-MPS-PLMA and TiO2-TMSP-PLMA composite particles were prepared by the in-stu radical polymerization, it was found that when the concentration of T-151was0.5mg/mL, TiO2-MPS-PLMA composite particles were negatively charged in tetrachloroethylene, the values of Zeta potential and electrophoretic mobility were maximum,23.1mV and3.56×10-10m2V-1s-1, respectively, when the concentration of Span80was10mg/mL, TiO2-TMSP-PLMA composite particles were positively charged in tetrachloroethylene, the values of Zeta potential and electrophoretic mobility were maximum,24.1mV and3.72×10-10m2V-1s-1, respectively. TiO2-g-PLMA composite particles were prepared by the surface-initiated ATRP. The maximum grafted amount was67wt.%. It was found that the stability of suspension was enhanced with the increasing grafted amount for the composite particles, under the influence of0.5mg/mL Span80, The Zeta potential and electrophoretic mobility were-19.5mV and-3.06×10-10m2V-1s-1.By means of strong interactions for polar groups, CB/T-151composite particles were prepared by self-assembly technique, it was found that the amount of T-151anchored on the CB surface was24.8wt.%, under the influence of10mg/mL Span80, The Zeta potential and electrophoretic mobility were9mV and1.51×10-10m2V-s-1. Four kinds of acrylic copolymer were synthesized by radical copolymerization, and then self-assembled on the surface of CB for CB/acrylic copolymer composite particles. It was found that the copolymers with PLMA segments improved the dispersibility and suspension stability of particles more effectively. When the feed ratio for DMAEMA:LMA was3:5, the prepared composite particles, CB/PDMAEMA-co-PLMA, had the maximum values of Zeta potential and electrophoretic mobility,32.5mV and5.44×10-10m2V-1s-1, respectively.Two kinds of dual-particle electrophoretic suspensions were selected based on the TiO2-MPS-PLMA composite particles and CB/PDMAEMA-co-PLMA, CB/T-151composite particles. It was found that the electrophoretic suspension composed of TiO2-MPS-PLMA and CB/PDMAEMA-co-PLMA showed good properties for electrophoretic cell, the reflectivity for white state was36%, the reflectivity for black state was0.4%, the contrast ratio was90:1. As for the electrophoretic suspension composed of TiO2-MPS-PLMA and CB/T-151, the reflectivity for white state was12%, the reflectivity for black state was0.4%, the contrast ratio was30:1.The block copolymer, PDMAEMA-b-PLMA, was synthesized by ATRP, and then, the CB/PDMAEMA-b-PLMA composite particles was prepared. The dual-particle electrophoretic suspension was prepared by selecting TiO2-MPS-PLMA as the white ink particles, it showed excellent properties for electrophoretic cell, the reflectivity for white state was43%, the reflectivity for black state was0.36%, the contrast ratio was120:1. In addition, the incorporation of PDMAEMA-b-PLMA block copolymer prevented the aggregation of ink particles during encapsulation by microcapsules. The EPD prototype devices were fabricated, when driven at9V voltage, the reflectivity for white image was36%, the reflectivity for black image was4.5%, the contrast ratio was8:1, the response time was1.4-2.0s.Red, Green%Blue and Cyan、Yellow、Magenta multicolor silica/organic pigments composite particles with core/shell structure were prepared by a general sol-gel methods. The particle sizes can be conveniently tuned by adjusting the concentration of the TEOS precursor. The silica coatings not only improved the reflectivity for pigments and made the particles more vivid, but also facilitated the adsorption of the PLMA-b-PDMAEMA block copolymer to enhanced the dispersibility and charging of the particles. The six electrophoretic particles with different colors present similar Zeta potentials and electrophoretic mobilities of about30mV and4-5×10-10m2V-1s-1, respectively. And then, the selected dual-particle color electrophoretic suspensions presented good optical properties and dynamic response.