Homeotropic alignment on surface-initiated liquid crystalline polymer brushes

Abstract

With the development of new types of liquid crystal displays and the use of liquid crystals as organic semiconductors, homeotropic alignment layers have become more and more important. Liquid crystalline polymer (LCP) brushes have been suggested as an alignment layer and are expected to have more interaction with the liquid crystal phase than other homeotropic alignment layers. Here we report the synthesis of side chain liquid crystalline polymer brushes by surface-initiated Atom Transfer Radical Polymerisation (ATRP) of an acrylate functionalized mesogen on glass and silicon substrates. Brush thicknesses up to 20 nm were achieved. Substrates coated with a brush layer of this polymer were used for alignment of the nematic liquid crystal 5-cyanobisphenyl (5CB). Nearly defectless homeotropic alignment over several square centimetres is demonstrated. Microcontact printing has been used to obtain a patterned alignment layer.