Synthesis of functional microcapsules containing suspensions responsive to electric fields

A sort of functional microcapsules, which contain a suspension responsive to electric fields, is prepared by in situ polymerization of urea and formaldehyde. The suspension is made up of pigment phthalocyanine green (PPG) and tetrachloroethylene. In order to solve the particles separation from the suspension during the microencapsulation and to obtain microcapsules applying to electronic ink display, the dispersibility of the particles, the contact angles between the particles and the tetrachloroethylene, and the influences of different emulsifiers on the microencapsulation are investigated. It is found that the dispersion extent and lipophilicity of the PPG particles are improved due to their surface modification with octadecylamine. The contact angles between the modified PPG particles and the tetrachloroethylene increase, and the PPG particles modified with 2 wt% octadecylamine have the best affinity for tetrachloroethylene. The interfacial tension between C2Cl4 and H2O with urea-formaldehyde prepolymer descends from 43 to 35 mN/m, which indicates that the polymer has certain surface activity. However, water-soluble emulsifiers have an important influence during the microencapsulation because they can absorb on the surfaces of internal phase and prevent the resin of urea-formaldehyde from depositing there. From the SEM images of shell surface and cross section, the microcapsules have relatively smooth surfaces and the average thickness is about 4.5 mu m. When the microcapsules are prepared with agitation rates of 1000 and 600 rpm, the mean diameters of the obtained microcapsules are 11 and 155 mu m, respectively. The particles in the capsules move toward positive electrode with a responsive time of several hundred milliseconds while providing an electric field. (c) 2004 Elsevier Inc. All rights reserved.