Transitions in a Spread Film of a Side-Chain Liquid Crystal Polymer

Abstract

A series of side-chain liquid crystal polymers have been screened for successhl deposition using the Langmuir Blodgett method. It was found that the best materials had glass transitions below room temperature. The behaviour of the spread film of one material was studied in detail using surface isotherms, surface potential, X-ray and neutron reflection techniques. It was found to undergo a phase transition from a thin, low density film to a thicker, more dense one as the surface pressure was increased. This corresponds to a reorientation of the mesogenic units so that about half of them point upwards. At higher pressure a transition to a multilayer occurs on the water surface. In the surface pressure range where deposition is possible, neutron reflection shows that the spread film has a stratum of close packed mesogenic units outermost and the total thickness (38 Å) agrees very well with the smectic layer spacing in the bulk. This similarity in structure could explain the ease of deposition.