The Effect of Aerosil Network on Liquid Crystal (4O.8) Phase Transition

We report a high resolution x-ray diffraction study of the nematic (N) to smectic-$A $(Sm$A) $transition in the single-layer smectic (Sm$A_{m})$ liquid crystal butyloxybenzylidene octylaniline (4O.8) within aerosil dispersion. Aerosils are dispersed in liquid crystal material with a broad range concentration. They dramatically affect the phase transition properties in different liquid crystals [1]. These effects were studied in the view of random field theory introduced by quenched randomness of the silica gel network. The second order N-Sm$A$ phase transition and strong first order Sm$A$-CrB freezing transitions are shifted to lower temperatures. Sm$A$ line-shape is broadened indicating a short-range order. Correlation lengths and power-law fits show behavior similar to bilayer Sm$A_{d}$ liquid crystals. The present work enables us to test our understanding of random field effects introduced by dispersed aerosils forming a network in Sm$A_{m}$ material. [1] S. Park, R.L. Leheny, R.J. Birgeneau, J.-L. Gallani, C.W. Garland and G.S. Iannacchione, Phys. Rev. E 65 050703(R) (2002)