The structural basis of transitions between highly ordered smectic phases in semifluorinated alkanes

Abstract

The semifluorinated alkanes F(CF₂)₁₀(CH₂)₉H and F(CF₂)₁₀(CH₂)₁₁H both undergo a reversible transition between tilted smectic phases above room temperature as demonstrated previously for F(CF₂)₁₀(CH₂)₁₀H. The transformation on cooling is achieved in two stages: an increase in molecular tilt relative to the layer normal, followed by a change in the molecular interdigitation within each layer. The extent of complete transformation is sensitive to temperature and time, due to strains occasioned by the accompanying volume change, and because the second stage requires significant molecular translations. Characterization of the transformation is possible by transmitted light microscopy, supplemented by X-ray diffraction.