Semi fluorinated polymers as surface energy controlled layers for liquid crystal alignment

Abstract

The effects of compounded hydrogenated–fluorinated surfaces formed by perfluorocyclobutane (PFCB)-containing polymers on the alignment of 4,4′-octylcycanobiphenyl (8CB), a liquid crystal that exhibits both nematic and smectic phases, were investigated. The inherent segregation between fluorine- and hydrogen-rich segments produced structured interfaces with fluorinated and protonated nano domains. The morphologies of the interfaces and their corresponding surface energies were probed by AFM and the alignment of 8CB was investigated by polarized optical microscopy. We found that varying the fluorine content controlled both the structure and the interfacial morphology. The 8CB layer orientation was strongly affected by the interracial energies. With increasing fluorine content the homeotropic alignment temperature range of 8CB in the nematic phase was increased and that of the smectic phase was hardly affected. The impact observed was attributed to competition between anchoring effects and elasticity of the LC layers.