Surface-induced orientational order in the isotropic phase of a liquid-crystal material

Abstract

Orientational order in the isotropic phase of liquid crystals confined to 0.2-μm-diam cylindrical channels of Anopore membranes is measured by deuterium nuclear magnetic resonance. At temperatures deep in the isotropic phase, the measurements reveal the order of the first molecular layer at the cavity wall, while at temperatures near the isotropic-nematic transition the measurements are primarily sensitive to order penetrating into the cavity in a manner described by the Landau–de Gennes theory. The degree of order ${\mathit{S}}_0$ at the cavity wall is measured and the surface coupling constant determined for various treatments of the cavity wall. Wide variations of ${\mathit{S}}_0$ are found for different surface treatments. Treatments that yield both perpendicular and parallel molecular anchoring are explored. The angular dependence of the surface-induced nematic order is investigated following the ${\mathit{P}}_2$(cosθ) expression independent of molecular anchoring at the surface.