Using light scattering, the thickness dependence of the isotropic-nematic phase transition temperature Tni in a thin film of octylcyanobiphenyl (8CB) is studied in two distinct geometries: with and without strain. We observed a large stress induced shift in TNI, as a function of the film thickness d. At d~ 0.3 fim a crossover in the behavior of TNI as a function of thickness is observed, which can be attributed to a competition between strain and anchoring forces. [S1063-651X (96)

The influence of confinement on the spectrum of collective excitations in ultrathin nematic layers of octylcyanobiphenyl is studied, using quasielastic light scattering in planarly and hybridly aligned films. Both systems show confinement-induced relaxation rate gaps in the originally gapless spectrum of director fluctuations. On the mesoscopic scale, the magnitude of the relaxation rate gap scales as the inverse thickness of the nematic layer and can be very well described by a Landau -de Gennes theory, in which the boundary conditions play an important role. [S0031-9007(98)

Light scattering by thin nematic liquid crystal films is considered. The confinement has two important consequences. First, fluctuations with wave vectors not equal to the difference between the wave vectors o f the scattered and the incident light ray can contribute to the scattering. The distribution o f fluctuation wave vectors relevant to the scattering is peaked around this difference and has a width inversely proportional to the film thickness. Second, only a discrete set of fluctuation wave vectors is allowed due to restrictions imposed by the boundary conditions. Consequently, the relaxation times of the different fluctuation modes depend on the film thickness. It appears that the relaxation time decreases due to the confinement. In the limit of vanishing thicknesses the relaxation time goes linearly to zero with the film thickness. The main conclusions are expected to hold qualitatively for other confined nematic systems, e.g., for nematics confined in porous media. [S1063-651X(96)00305-4] PACS number(s): 68.10.Cr, 64.70.Md

The phason dispersion in the antiferroelectric Sm-c: liquid crystalline phase of 4-(1-methylheptyloxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate has been studied by quasielastic light-scattering experiments. The phason is found to be gapless as predicted for a Goldstone mode recovering the broken continuous symmetry. The dispersion has a minimum at q -2qc, where qc is the wave vector of the unperturbed Sm-C:l' structure. These results are consistent with the alternating-tilt model of the antiferroelectric Sm-C:l' phase.

The exchange behavior between proteins and surfactants at the water-air interface has been studied using optical second harmonic generation and ellipsometry. At low surfactant concentrations the proteins force the adsorbed surfactants to dissolve, whereas at higher concentrations a double layer is formed with the surfactants on top of the proteins.