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.

The magnetization recovery of a two-dimensional ferromagnetic system after excitation by intensive ultrafast pump pulses is investigated by a Monte Carlo method with a focus on the evolution of domain structure and the magnetization in the equilibrium state. Our simulations can explain the effect of the pumping fluence on the recovery process. In particular, they reveal the importance of domain formation in the recently reported accumulation effect already found by the pump-probe magnetization hysteresis loop measurement of a metallic ferromagnetic film. In the framework of the model, it is predicted that by repeating pump pulses a sufficient number of times, the magnetization of the two-dimensional ferromagnetic system can be eliminated when the pump fluence is above a critical value. #

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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.

Mechanical rubbing of polyimide (PI) films is used to homogeneously align liquid crystal molecules on the surface. The chemical structure of aromatic PI surfaces subjected to rubbing has been analyzed by X-ray photoelectron spectroscopy, and the frictional charging and surface states of the PI films have also been investigated by measurements of surface potential (SP) and photoelectric emission (PE).Six kinds of PI films were prepared by reacting two diamines containing CH3 and CF3 functional groups with three tetracarboxylic dianhydrides.Rubbing of the films caused the O content to increase, while the N and F contents decreased.The fraction of the two oxygen components (-O-and C =O) of the films was changed by the rubbing.The films with CF3 groups exhibited much more negative charging (negative SP) than those with CH3 groups.It is suggested that the order of the charging of the films with CF3 and CH3 groups closely depends on the ratio by which the F and N elements, respectively, were reduced by the rubbing.Both with and without rubbing, the films with CH2 groups gave a considerably larger PE level than those with CF3 groups.This suggests that the electron trap levels responsible for the negative charging in the latter films make virtually no contribution to PE.

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