Surface-Freezing Transitions and Novel Tilted Hexatic Phases in Smectic Liquid-Crystal Films

Abstract
We report the first unambiguous identification in a thermotropic liquid crystal of a hexatic smectic- L, a phase with molecular tilt direction intermediate between those of the smectic- I and smectic- F, using electron diffraction in free-standing films of 5-(4′′-hexyl,3′-fluoro-p-terphenyl-4-oxy)-pentanoic acid ethyl ester. Our structural data directly support the proposed explanation of the unusual stripe phase observed optically. We also describe multiple surface-freezing transitions which occur at lower temperatures and involve novel tilted crystal phases.