The orientation of functional groups, side chains, and repeat units at the surface of a liquid crystal (LC) alignment layer (AL) polyimide was changed by rubbing with a cotton velvet cloth. It was discovered that rubbing induced polar functional groups and repeat units to reorient out-of-the-plane of the surface, and it made nonpolar aliphatic side chains partially reorient inward, toward the bulk of the film. The polar AL surface provided relatively small LC pretilt angles while polyimides with long alkyl side chains gave relatively large LC pretilt angles. The results suggest that LC pretilt angles are greatly affected by both electronic interaction and steric repulsion between LC molecules and an alignment layer polyimide surface.

An explanation for the mechanism generating a pretilted nematic liquid crystal conformation aligned on rubbed alkylbranched-polyimide layers is given based on a steric interaction model. An analytical calculation using this model was shown to agree fairly well with the data of torsional coupling strength obtained in this work.

The local electronic structure of intrinsic defects. including antisites, interstitials, vacancies and complexes with themselves or with Si impurities, in a (GaP),/(InP)) (001) strained-layer superlattice determined by the Keatingmodel, iscalculated using a developed recursion method. Besides the localized states obtained, attention is paid to the electronic hlcupancyon various defects. Ageneralconsequenceofdescribing the influenceofisolated defects on the electron distribution of their neighbours is given. It is found that the charged state of an atom will be changed when it becomes an antisite. A closely bound (ITP,,,) (I11 Ga or In) pair, formed by coulombic interaction, will induce some states in energy gap. No evidence is found anywhere of EL2-like behaviour in this system. Some novel diffusionmechanisms, basedonIpandVpcomplexformationanddissociation, arepresented.

SAXS by solutions of monodisperse polystyrene at intermediate concentrations has been studied for the solvents having only a small volume‐exclusion effect, such as methyl ethyl ketone (MEK) and cyclohexane (CH). Both the density‐density correlation function of segments in solution and the osmotic compressibility, as obtained from the absolute intensity at zero angle, were measured for different concentrations and the results were successfully analysed by means of the recent theory of Moore [J. Phys. (Paris), (1977), 38, 265–271] . According to the theory, in the semi‐dilute poor‐solvent regime the concentration C, dependence of the screening length ξ, and the scattered intensity at zero angle I(0) are given by = 12NA + 36N2AC and = B1 + 3NAB2C, where M is the molecular weight of a polymer molecule, NA Avogadro's number and A2M the mean square end‐to‐end distance of an unperturbed chain; m2B1 and m3B2 are respectively the binary and ternary cluster integrals (or the first and the second irreducible integrals) for segments in solution, m being the molecular weight of a segment. ΔZ is the number of excess mole electrons per unit mass of segments. The measured concentration dependences were in agreement with the above prediction and the values of B1 and B2 were obtained.