(A) study on the effect of onium salt on the electro-optic properties of PDLC

Abstract

In this paper were studied different types of the polymers with glycidyl groups as Polymer Dispersed Liquid Crystal (PDLC) matrix and improvement of PDLC performance of them by new preparation. The types of commercially standard epoxy resin, hereinafter referred as Epon828 system, and acryl resin with epoxide group, hereinafter referred as glycidyl methacrylate/methyl methacrylate (GMA/MMA) system, were chosen on the basis of ring-opening cure mechanism of epoxide with cationic photoinitiator by UV irradiation. These polymers were used as PDLC matrix by new technique of phase separation. This method is cationic photo-cure using onium salt which has been well known as Photoacid generator (PAG). The effect of PAG in the polymer was measured by dielectric analysis and studied for the correlation with threshold voltage ($V_{th}$) and rise time ($\tau_r$) by PDLC characterization. Spectral and thermal analysis show that PAG operates as cationic photoinitiator. It is observed that PAG which is used as cationic photoinitiator also functions as dopant generating ionic conductivity in the matrix by comparing DEA results of PAG-free systems with PAG-contained systems. The ionic conductivities of PAG-contained systems were very sensitive to frequency, temperature, and concentration of PAG. In comparison with photo-cured Epon828 systems, $V_{th}$ decreased with an increase of the concentration of PAG and the size of anions (dopants) generated from PAG by UV dose. In GMA/MMA system, these results also were observed. But it could be assured that the increase of glycidyl moiety in acryl system had no influence on the ionic conductivity of system and $V_{th}$. It could be observed that photo-cured Epon828 system shows the dielectric behaviors of the binary series co-continuous model. This was confirmed by correlating the experimental data of photo-cured Epon828 system with the electrical characteristics of this model which is induced from the dielectric theory, on low and high...