Fabrication of Polymeric Capsules Enclosing Eletrophoretic Particle Dispersion
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0949-C02-03
Fabrication of Polymeric Capsules Enclosing Eletrophoretic Particle Dispersion Ru Qiao, Xiao Li Zhang, Ri Qiu, Yan Li, and Young Soo Kang Department of Chemistry, Pukyong National University, 599-1 Daeyeon-3-dong, Namgu, Pusan, 608-737, Korea, Republic of
ABSTRACT Poly(urea-formaldehyde) capsules enclosing electrophoretic particle dispersion were formed by carrying out an in-situ polymerization reaction in an oil-in-water emulsion. The internal dispersion was composed of pigment particles Yellow-14 modified by charge control agent to have superior electrophoresis velocity and the mixture of tetrachloroethylene and secbutylbenzene, using Span 80 as the stabilizer and emulsifier. FE-SEM, TEM, and optical microscope (OM) were performed to investigate on the capsule size and surface morphology. Contact angle measurements showed that UF prepolymer deposited at the o/w interface to form hollow capsules only when the interfacial tension is large enough. INTRODUCTION Recently, capsules having a liquid core and a polymeric shell have been used in many fields such as recording materials1-3, agrochemicals4, medicines5,6, and electrophoretic display elements7-13. Capsules of this type range in size from less than a micron to a few millimeters. Chemical functionality or biocompatibility can be achieved through the use of an appropriate shell polymer. As the method of producing capsules, many methods have been proposed, and known typical methods include a coacervation method, an interfacial polymerization method, an in-situ polymerization method, etc. In this paper we reported the synthesis of poly(urea-formaldehyde) (PUF) capsules containing electrophoretic particle dispersion to be used as electrophoretic image display (EPID) elements. The product was prepared by in-situ polymerization14-16 by first preparing a UF prepolymer in solution conditions, followed by addition of the internal suspension to the polymerization solution and depositing of the UF polymer at the o/w interface. In particular, our interest was devoted to a better understanding of the influence of the reaction parameters on the encapsulation of the core material. Key process parameters, involving the reaction time of prepolymerization, the type of surfactant and the surfactant content in water phase, affecting the formation and the properties of capsules, were investigated in detail. Furthermore, the response behavior of the electrophoretic particles to electric field was studied, and the surface morphology of the capsules was also characterized by FE-SEM and OM. EXPERIMENT 2.1 Surface Modification of Yellow-14 Particles and Preparation of Core Materials. Polyethylene (PE) was dissolved in cyclohexane with stirring at 80 , and then Yellow-14 pigment particles were sonicated in the above solution for several minutes. After placed for 24 h,
the mixture was centrifuged at 3000 rpm for 5 min. The obtained particles were washed by anhydrous methyl alcohol and dried at 50 . The pigment particles modified by PE were obtained. Modified Yellow-14 particl
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