| Summary: | 碩士 === 輔仁大學 === 化學系 === 93 === Polymer dispersed liquid crystal (PDLC) composite films have been the subjects of much research in recent years due to their usefulness in making displays and switch windows. Such a PDLC film is usually a translucent thin film since there is a mismatch existed between the refractive index of the LC droplets and that of the polymer matrix. The effective refractive index of the LC droplets depends on the configuration of the LC directors and the LC orientation.
In this study, the induction of LC orientation through mechanical stretching was investigated for E7 (mixture of 5CB, 7CB, 8OCB, and 5CT)/PMMA [poly(methyl methacrylate)]PDLC system by means of dielectric and SEM analysis. This study revealed that the dielectric constant and opaqueness of the PDLC film increased with the content of LC in the polymer matrix. The sample with 30% ( ) LC exhibiting an average LC droplet size of 2~3μｍ gave the highest extent of transmittance. And it was found that the stretching operation did decrease the dielectric constant of the PDLC film and increase its transmittance as well. The dielectric constant increased from 3.0 to~11.0 (measured at 1kHz) as the content of LC E7 increased from 0% to 40% (by wt.), while the transmittance of the composite film decreased from 70% to 36%. The orientation of LC molecules within the LC droplet were changed upon stretching operation, this led to the lowering of dielectric constant of the composite film tested along the stretching direction. The film of E7/PMMA (30/70, by wt.) gave a lowest value of dielectric constant of 4.7 as it was stretched to an elongation of 85%.
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