(A) study on the ionic conductivity effect of polymer matrix on the electro-optic properties of PDLC

Abstract

Most of polymer-dispersed liquid crystal (PDLC) films are many electrooptical properties to be required in a projection display such as low driving voltage and short response time. In order to improve these properties, a new effect of the electrooptical properties of PDLC film on the ionic conductivity and dielectric property of the matrix polymer has been investigated. The effect of ion generator in the polymer was measured by dielectric analysis and studied for the correlation which threshold voltage ($V_th$) and rise time ($τ_r$) by PDLC characterization. Poly(poly(ethyleneglycol)oxycarbonyl)-bicyclo[2.2.1]hepta-2,5-diene), poly(2-ethyloxycarbonyl-bicyclo[2.2.1]hepta-2,5-diene-co-poly(ethylene glycol) methacrylate), 2,2-Bis(4-(2,3-epoxypropoxy phenyl)-1,1,1,3,3,3-hexafluoropropane, and 4``-(6-(4-Aminophenoxy)hexyloxy)-4-cyanobiphenyl were synthesized and evaluated as electrooptical properties. The ionic conductivities of the poly (PEGOC-BCHD)/$LiClO_4$ for various molecular weights of PEGs increased with the increase of Li/EO ratio and the increase of the chain length of the PEG substituent because of the increase in the number of charge carriers. Transmittance of poly(PEGOC-BCHD)/E8 for various chain lengths of PEGs increased with electric field up to 1.0-1.2 V/㎛. The influence of transmittance as a function of electric field for various Li/EO ratios and the molecular weights of PEGs shifted to the higher values with the increase of the lithium salt concentration because the ordinary refractive index of the LC matches more closely with that of the polymer. $V_th$ and $τ_r$ were remarkably improved with the increase of conductivity of the matrix polymer. The magnitude of the electric field in the LC phase is strongly dependent on the conductivity of the matrix polymer. Thus the matrix polymer with larger conductivity led to improvement of $E_th$ and $τ_r$. Ionic conductivities of the poly(MOCBCHD-co-PEGMA)/$LiClO_4$ for various content of PEGMA systems incr...