ALKYLENE POLYIMIDES FOR ALIGNING NEMATIC LIQUID-CRYSTALS - ANOMALOUS ODD-EVEN EFFECT IN TILT BIAS ANGLES AS A FUNCTION OF CHAIN-LENGTH OF ALKYLENES

Measurements of tilt bias angles of a nematic liquid crystal were carried out, by using several alkylene polyimides synthesized from 3,3',4,4'-biphenyltetracarboxylic dianhydrides and diamines with different chain lengths as alignment layers. The tilt bias angle dependence on the alkylene chain length of polyimides shows an anomalous odd-even effect. Small tilt bias angles, less than one degree, were observed with odd-number alkylene chain lengths. Relatively high tilt bias angles, however, were observed with even-number lengths. We have made an attempt to explain this effect from X-ray diffraction and scanning electron microscope measurements and molecular mechanics calculations of the polyimides with alkylene chain. As a result, this odd-even effect of the tilt bias angle is due to the difference of surface structures between alkylene polyimides with odd alkylene lengths and those with even ones.