Electro-optical switches based on Polymer and Dendrimer Filled Nematics

Two-phase systems which can be switched electrically between a light scatte ring and a transparent state can be prepared based on either a dispersion o f well-defined sub-micron sized crosslinked polymeric particles in a liquid crystal (LC) matrix (Polymer Filled Nematics, PFN's) or on a dispersion of palmitoyl-functionalised poly(propylene imine) dendrimers in an LC (Dendri mer Filled Nematics). The present paper describes the preparation of both s ystems and their properties. The PFN's can be electrically switched between a scattering and a transparent state by an appropriate choice of materials and refractive indices. The preparation of the disperse polymeric phase is separated from the preparation of the polymer/LC blend, which enables cont rol over the morphology of the system. Rather surprisingly, it is found tha t, due to the rheological properties of the PFN blends, stable films of the blends can be simply produced by conventional coating processes. The dendr imer-stabilised nematics require extremely low switching voltages to switch from a scattering to a highly transparent state. Moreover, the switching p rocess is totally reversible and hysteresis effects appear to be absent.