Construction And Performance Study Of Titanium Dioxide Electrorheological System Modified With Methylacrylate And Application In Electrophoretic Display

A series of titanium dioxide nano particles modified with poly(methyl acrylate)(PMMA/TiO2, PBMA/TiO2, PEHMA/TiO2, PLMA/TiO2 and PSMA/TiO2) were prepared via in-situ polymerization using MMA, BMA, EHMA, LMA and SMA as monomer. The modified particles were characterized by Fourier transform infrared, thermogravimetry, scanning electron microscopy and transmission electron microscopy. With the increase of carbon numbers of alkyl chains in poly(methyl acrylate) substituent, the water contact angle of the modified particles increased accordingly. Meanwhile, the surface of the particles changed from hydrophilic to hydrophobic and the aggregation state turned to well dispersion gradually in organic solvent. The Zeta potential and electrophoretic mobility of modified particles were both increased in Isopar L while the stability of dispersion was enhanced. The average diameter of titanium dioxide was relatively large and the aggregation and sediment phenomenon could be observed if the carbon numbers of alkyl chains in substituent was less than 8. While we could get relatively small particles ranged from 200~300 nm and well dispersed system if the carbon numbers was higher than 8.A novel non-aqueous electrorheological(ER) fluid structured by TiO2 nano-particle modified poly(methyl alkylacrylate)(PMMA/TiO2, PBMA/TiO2, PEHMA/TiO2, PLMA/TiO2 and PSMA/TiO2) dispersed in low viscosity Isopar L were fabricated and its electrorheological behaviors were studied. The research results showed that the PLMA/TiO2 ER fluid performed the best rheological property when an external electric field was applied and followed by PMMA/TiO2. The PBMA/TiO2 and PSMA/TiO2 exhibited almost equal electrorheological behaviour while PEHMA/TiO2 had no effect. Without the external electric field, the ER fluid behaved as typical Newtonian fluid. The shear stress was increased when an external electric field was applied from 0 to 4.5 k V/mm which demonstrated the characteristic of Bingham fluid. Meanwhile, the electrorheological effect and shear stress were also strengthened with temperature elevated and the mass concentration of solid particles increased in dispersed system, respectively. The electric field intensity, mass concentration of solid particles and shear rate all had an impact on the leakage current of the ER fluid and the corresponding threshold could be observed. The dielectric constant and dielectric loss as well as the ER effect increased with the increase of the mass concentration of solid particles.The PMMA/TiO2, PBMA/TiO2, PEHMA/TiO2, PLMA/TiO2 and PSMA/TiO2 ER fluid were applied in the electrophoretic display as white medium and the display properties were investigate. The results showed that the response time of the electrophoretic display prototype device prepared with PLMA/TiO2 ER fluid as white medium was the shortest which was 300~400 ms and the contrast ratio was 7 as well as the transient current and leakage current can be effectively restrained. While the contrast ratio of the electrophoretic display micro-cup device prepared with PLMA/TiO2 ER fluid as white medium was 2.6, the steady state kept for more than 24 hours.