Structure and Phase Behavior of Smectic Liquid Crystals in Anisotropic Disorder

We present x-ray scattering studies of the smectic liquid crystals octylcyanobiphenyl (8CB) and 4-n-pentylphenylthiol-4-n-octyloxybenzoate ($\bar {8}$S5) confined in strained colloidal silica gels. The gels possess anisotropy that stabilizes long-range nematic order in the liquid crystals while introducing random field effects that disturb the smectic order. The strong azimuthal focusing of the scattering enables detailed characterization of the smectic correlations. The short-range smectic order that forms in this environment is inconsistent with a topologically ordered state predicted for 3D random field \textit{XY} systems and is quantitatively like the correlations of smectics confined by isotropic gels. The quenched disorder modifies the nematic -- smectic-A critical behavior, for example, suppressing the anisotropic scaling of the correlation lengths observed in the pure liquid crystals. The smectic-A and smectic-C scattering indicates that the behavior of smectics confined in gels is dictated by random fields coupling directly to the smectic order parameter while fields coupling to the nematic director play a subordinate role.