Light-scattering and ellipsometry studies of the two-dimensional smectic-Cto smectic-Atransition in thin liquid-crystal films

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Abstract
Ellipsometry and light-scattering measurements are presented for the critical region near the two-dimensional XY-like smectic-C to smectic-A phase transition in thin, freely suspended films of the liquid crystal p-decyloxybenzylidene p-aminocinnamaic acid 2-methylbutyl ester. The macro- scopically observed smectic-C tilt order parameter was found to obey a scaling relation as a function of temperature and film thickness, indicating that only the surface layers order over a wide range of temperatures. Deep within the smectic-C phase, the tilt order parameters for all thickness films measured converged upon a unique value at which the smectic-C to smectic-I transition took place. The light-scattering intensities and decay times above the smectic-C to smectic-A transition were found to scale with the Kosterlitz-Thouless correlation length, as predicted by dynamical theories of the transition. Measurements of the predicted Nelson-Kosterlitz universal jump in θ concurred with estimates for the bulk material parameters and with the light-scattering results.