RUBBING STRENGTH DEPENDENCE OF SURFACE INTERACTION POTENTIAL AND SURFACE-INDUCED ORDER ABOVE THE NEMATIC-ISOTROPIC TRANSITION

Optical retardation measurements as a function of rubbing strength are reported for both rubbed polyimide-coated substrates and cells contai ning the liquid crystal hexylcyanobiphenyl. Our analysis assumes a She ng surface interaction potential of the form -GS(s) delta(z), where S- s is the order parameter of the liquid crystal at the interface and G is related to the rubbing strength. Moreover, we assume that there can be a distribution Delta G in the parameter G. Several features are no ted: There appears to be a minimum rubbing strength before the onset o f substantial surface-induced order in the liquid crystal; the paramet er that characterizes the interaction potential between the polyimide and liquid crystal is proportional to the optical retardation of the p olyimide-coated substrate; and, in light of our analysis, there are su bstantial inhomogeneities in the liquid crystal interaction potential and surface order parameter, perhaps even on length scales comparable to the nematic correlation length. (C) 1998 American Institute of Phys ics. [S0021-8979(98)00323-5].