Open Access Kent State (OAKS)

The formation of different structures in phase-separated composite films (PSCOFs) from formulations of liquid crystals and photocurable monomers has been investigated using polarizing optical and scanning electron microscopies. Two processes, spatially nonuniform polymerization and diffusion of small molecules, play important roles in determining a specific PSCOF polymer structure. The variations in UV irradiation intensity and temperature, at which phase separation is carried out, strongly influence these two processes and can change the resultant structure from a homogeneous PSCOF bilayer structure to a heterogeneous polymer dispersed liquid crystal (PDLC) structure. A variation in cell thickness changes the distance through which small molecules have to diffuse during phase separation and, thus, affects the structure obtained in thick and thin cells.

We review recent developments in the use of the phase separated composite organic film method and the fabrication of liquid crystal (LC) electro-optical devices using a single glass substrate using this method. The LC layer is confined between a film of solidified polymer layer on one side and the glass substrate on the other. The solidified polymer layer adjacent to and parallel to the LC layer is created by UV induced phase separation of a mixture of LC and prepolymer. Electro-optical properties of these devices demonstrate their high technological potential in light weight and hand-held electronic products

Phase separation of liquid crystals from a solution with polymers has long been studied and used to prepare polymer stabilized and polymer dispersed structures. They are formed by spatially isotropic phase separation. A new mode, in which the phase separation proceeds anisotropically, has recently been discovered. Known as phase separated composite films (PSCOF), the resultant structures are made of adjacent parallel layers of liquid crystal and solidified polymer. PSCOFs have been made with nematic, ferroelectric (FLC), and antiferroelectric (AFLC) liquid crystals. Liquid crystals in PSCOFs exhibit electro-optical properties not observed in devices prepared by conventional methods, polymer dispersion, or polymer stabilization methods. Devices incorporating FLCs possess grey scale and switch 100 times faster at low fields than conventional surface stabilized devices. This method makes it possible to prepare very flexible devices and devices with liquid crystal film thickness comparable to optical wavelengths with great ease.