Chapter 7: Polymer-stabilized Nematics and Their Applications

The addition of a polymer network to nematic liquid crystals (LC) was a notable milestone in the research and development of liquid crystalline materials. It was found that, not only did it improve the ruggedness and stability of the resulting films and devices, but it also increased the diversity in the electro-optic characteristics, and in some cases yielded important improvements in the resulting device performance. Polymer-stabilized nematics are composites that are typically obtained by doping a relatively small concentration by weight (typically <10wt%) of a polyfunctional monomer into the LC solvent. When cross-linked this leads to an interpenetrating polymer network that stabilizes, and to some degree phase separates from, the nematic host. These materials exhibit macroscopic physical and electro-optic properties that readily distinguish them from conventional side and main chain elastomers/polymers and polymer-dispersed LCs. In this Chapter, our objective is to consider the role that the polymer network plays on the resulting electro-optic characteristics of nematic LCs, primarily the threshold voltage and response times. Their behaviour will be compared with that observed in conventional, non-polymer-stabilized nematic devices. We also consider the experimental results obtained for different device architectures in which polymer-stabilization has been implemented and the advantages and disadvantages of introducing a polymer network for the electro-optic properties. The Chapter concludes with a brief overview of the role advanced fabrication techniques might play in the future development of polymer-stabilized nematic LCs and the use of polymer-stabilization to form tuneable microlenses.