Controlling the morphological and electro-optical properties of polymer dispersed Liquid crystals

Abstract

Polymer dispersed liquid crystals have shown potential as the basis for a new display screen technology which can be used to produce flexible displays. The work presented here investigates the properties during the synthesis process of PDLCs, which affect the electro-optical properties of the films produced. An investigation is performed through the use of small angle light scattering, and small angle neutron scattering, into the thermodynamic phase properties of the initial liquid crystal monomer solution from which the PDLCs are formed. Through the use of small angle light scattering and ESEM the phase separation mechanism is determined and the morphological properties of films formed under different thermodynamic conditions are investigated and linked to the electro-optical properties of test films. It is shown that due to the rod like nature of liquid crystal molecules that the monomer/liquid crystal phase properties cannot be explained by classic polymer solution thermodynamics. Phase separation is shown to occur by one of two mechanisms depending upon whether or not a crosslinking monomer species is present, either a gel phase separation mechanism or a viscoelastic mechanism. Depending upon the initial thermodynamic properties of the system the formation of a polymer network can either act to promote (resulting in a large droplet morphology size) or suppress (resulting in small impure liquid crystal droplets) phase separation. This in turn is linked to the effectiveness of films formed under given conditions as potential display devices. With thanks to EPSRC and Sony MSL, Stuttgart for funding