Physics of liquid crystals embedded in silica gels

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2001.Includes bibliographical references (p. 127-130).Octylcyanobiphenyl (8CB) embedded in silica aerosil gels have been studied by means of high resolution X-ray scattering experiments. The silica particles form a hydrogen-bonded fractal gel network that introduces quenched disorder. As a result, the nematic to smectic-A transition is replaced by the growth of static short range smectic correlations. The X-ray scattering profile has two contributions: a thermal fluctuation term which resembles that of the pure liquid crystal and a static fluctuation term due to the random field that becomes important at low temperatures. The decrease of the smectic correlations with increasing silica density is consistent with theory and other experiments.by Sungil Park.Ph.D