Simplified preparation of polymer-encapsulated LC layers by thermally induced phase separation

Abstract

Stabilisation of functional layers in flexible liquid crystal displays (LCDs) is essential if they are to find use in advanced applications. Among the various methods for encapsulation of liquid crystals (LCs) by spatially controlled polymer wall formation within LCD cells, we have devoted particular attention to thermally induced phase separation (TIPS) in LC/polymer systems. A drawback of the standard TIPS procedure is the requirement to fill cells with the isotropic LC/polymer mixture at elevated temperatures. We have demonstrated that compartmentalisation can be simplified by precoating the substrate with an appropriate thermoplastic matrix polymer, for example poly(1-tetralyl methacrylate) (PTMA), before assembling and filling the cell with polymer-free LC at ambient temperature. The insular morphology originating from subsequent TIPS in different types of display cells prepared with nematic or chiral nematic mixtures has been examined by polarising microscopy and scanning electron microscopy. The electro-optical characteristics of test devices based on polymer-free LC films or on LC/polymer composites, prepared by both standard TIPS and our novel technique, are compared.