Smectic-AOrder at the Surface of a Nematic Liquid Crystal: Synchrotron X-Ray Diffraction

Abstract

A novel geometry in which it is possible to do x-ray diffraction from a horizontal surface of fluids is applied to liquid crystals. A large-diameter drop of octyloxycyanobiphenyl (8OCB) on a glass plate treated for homeotropic alignment yields perfect alignment of the smectic-$A$ layers at the top surface over an area of several square millimeters. The surface in the bulk nematic as well as in the isotropic phase was found to consist of smectic-$A$ layers with a penetration depth equal to the longitudinal smectic-$A$ correlation length ${\xi }_{\parallel }\sim {(T-T_{\mathrm{NA}})}^{-{\nu }_{\parallel }}$ determined previously.