Amphiphilic Langmuir-Blodgett films as a new tool for inducing alignment transition in nematics

Mono- or multilayers of egg lecithin, distearoylphosphatidylcholine lecithin (DSPC-L), dimiristoyl-phosphatidylcholine lecithin (DMPC-L) and stearic acid (SA) deposited by Langmuir-Blodgett technique were used as aligning films in a nematic liquid crystal cell for obtaining a uniform homeotropic orientation and a temperature driven surface transition close to the clearing point. An excellent homeotropic alignment of the liquid crystal was obtained when a monolayer of DMPC-L, DSPC-L or SA was used. In these cases, a sharp and reversible transition from the homeotropic orientation to a set of circular domains, where the liquid crystal molecules have a degenerate quasi-planar alignment, was observed a few tenths of a degree below the nematic-isotropic phase transition.