Electroclinic Liquid Crystal Materials for Electrooptic Imaging

摘要

The correlation between molecular structure and electrooptic performance is studied for two series of ferroelectric liquid crystalline materials. The first series (Series 1) consist of siloxy units attached to the hydrocarbon chain at the non-chiral end of the molecule; while the second series (Series 2) contain only hydrocarbon chains at the end of the molecule. Series 1 exhibit chiral smectic A (SmA) and smectic C (SmC). It is observed that slight modifications in either the siloxy or the hydrocarbon chain length has strong effect on the electrooptic properties. Increasing the number of siloxy unit in the chain (Series 1) increases the temperature range of SmA, and reduces the SmA-SmC transition temperature. All materials have melting temperatures below room temperature, and exhibit high values of induced tilt angles. In Series 2, the materials show a broad SmA temperature range, and melting temperatures much higher than in Series 1. However, the SmA phase is found to supercool to subambient temperatures. If the hydrocarbon chain is shortened, tilt angle, electroclinic coefficient and switching time are significantly suppressed. Comparison of the electrooptic performance in SmA between the two series show that Series 1 show a much higher tilt angles than Series 2, while the later exhibit much faster response times.