Preparation Of TiO₂Nano-particles With Controllable Surface Charges And Study Of Electrophoretic Display Materials

Titania nano-particles with controllable surface charges for electrophoretic displaywere prepared in this thesis. Then new environmental friendly electrophoreticdispersion liquid with Isopar L as dispersion medium was investigated. At last, stabledisplay of electrophoretic dispersion liquid was preliminarily studied.Titania nano-particles were modified by anionic surfactants, cationic surfactants aswell as polymers respectively and analyzed by IR, TG, TEM, SEM and so on. Titanianano-particles with low density, uniform particle size and lipophilic surface wereobtained. Preparation of titania nano-particles with controllable surface charges wasinvestigated with ethylene tetrachloride, Isopar H and dodecylbenzene as dispersionmediums. The research results showed that titania nano-particles modified by cationicsurfactants showed negative charges in ethylene tetrachloride, while positive chargesin Isopar H and dodecylbenzene; titania nano-particles modified by anionicsurfactants displayed the opposite character. The ξ potential of titania nano-particlesmodified by sodium dodecylbenzenesulphonate, hexadecyl trimethyl ammoniumbromide and styrene/divinylbenzene respectively reached a minimum value near thecritical micelle concentrations of charge control agents, and a regular change with theincreasing concentration, while the charge property of ξ potential was still maintained.According to this observation, preparation of controllable surface charges of titanianano-particles could be achieved. The display results of modified titanianano-particles were discussed. The results showed that the contrasts of electrophoreticdispersion liquids with titania nano-particles modified by sodiumdodecylbenzenesulphonate, hexadecyl trimethyl ammonium bromide andstyrene/divinylbenzene respectively were improved, especially modified byhexadecyl trimethyl ammonium bromide with concentration of0.02%.Methods of preparation of electrophoretic dispersion liquids were studied byorthogonal experiment via dispersing titania and carbon black in Isopar L. Theoptimal concentrations of titania particles, carbon black particles, CH-5, T151,perfluoro-1-octanesulfonyl fluoride and A4300were30%,5%,2%,1%,1.91%and0.75%, respectively. The ball milling times of black electrophoretic dispersion liquidand white electrophoretic dispersion liquid were24h and36h, respectively. The optimal particle weight ratio of carbon black/titania was0.01. The contrast ratio ofprototype display device prepared by above processes was27.54, and response timesof black state and white state were880ms and1093ms, respectively.The influence of polyisobutylene and physical parameters of electrophoreticdispersion liquid on display and steady-state time was investigated. The resultsindicated that the increased polyisobutylene concentration led to the decreasedcontrasts ratio and extended response times. The steady-state times increased firstlyand then decreased as the polyisobutylene concentration increased. The longeststeady-state time (106s) could be obtained when the concentration of polyisobutylene(400000molecular weight) was1%in the electrophoretic dispersion liquid. Thesteady-state time of electrophoretic dispersion liquid increased with its permittivityand viscosity increasing. When the viscosity of electrophoretic dispersion liquidchanged little, the steady-state time decreased with the increase of conductivity. Theelectrophoretic display device showed long steady-state time when the transientcurrent of charge and discharge was small.