Hisao Yokokura

Alkylene polyimides for aligning nematic liquid crystals : anomalous odd-even effect in tilt bias angles as a function of chain length of alkylenes

Abstract 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.

Experimental Evaluation of Surface Tension Criteria for Alignment Behavior of Liquid Crystals on Solid Surfaces

Experimental verification has been carried out the surface tension difference criteria for liquid crystal alignment on solid surfaces. Organic polymer films, with surface tension values controlled from 16.0 to 44.8 mN/m (which includes the surface tension of liquid crystal ZLI-1132) were examined. On films thick enough to avoid undesirable topological effects ( >80 nm), the surface tension value at which the surface changed from a homogeneous to a homeotropic alignment was 31.2 mN/m, which is very close to the 31±0.5 mN/m value of ZLI-1132.

New Electrooptic Switching in Ferroelectric Liquid Crystal Cells

A new type of the director orientation structure was proposed and the associated new switching process was discussed in a homogeneously aligned ferroelectric liquid crystal cell. The cell had a helicoidal structure and the director on each surface aligned in the same direction. An apparent uniform state was obtained except around the disclination lines. The disclination behavior plays an important role in the switching process and provides several advantages such as a memory effect and nucleation control for a display application.

Pre-tilt angles as a function of polyimide composition for copolyimides

Six series of copolyimides have been synthesized. The pre-tilt angle has been measured as a function of the composition of these copolyimides. A linear relationship was found between the pre-tilt angle and the composition when both the simple polyimides are amorphous. When one or more of the simple polyimides is semi-crystalline there is normally a strong deviation from linearity. The copolyimides will then usually give pre-tilt angles lower than expected from an average of these for the two simple polyimides.