An investigation of patterning anisotropic gels for switchable recordings

Abstract

A new kind of anisotropic gel has been produced by photopolymerization of liquid crystal (LC) mixtures composed of monoacrylates, diacrylates and non-reactive conventional LC molecules. After polymerization, lightly cross-linked anisotropic polymer networks swollen by the non-reactive molecules are produced. These systems showed a gel-point associated with the onset of the formation of a three dimensional network. Above this point, a rapid increase in the threshold voltage was observed. Various factors, such as the photoinitiator concentration and the monoacrylate and diacrylate concentrations, as well as the intensity of the light used for the polymerization, have a strong influence on the gel-point. The switching kinetics of the materials are also strongly influenced by the aforementioned parameters. Two relaxation processes were found to occur within the gels above the gel-point. Using dielectric spectroscopy, this behaviour was found to be associated with an inhomogeneous phase structure within the gels. Patterned irradiation was used to produce regions with different threshold voltages for switching. In this way, patterns were created in the gels, which become visible, by the application of an electric field. It was demonstrated that this technique can be used to produce switchable gratings, Fresnel lenses, and photographs.