| The concept of electronic paper is very attractive to consumers. It offers the possibility for a thin, reflective, lightweight, flexible device that uses little power. There are many particle display technologies in competition to meet requirements for electronic paper, but they all have disadvantages.; Polymer cholesteric liquid crystal (PCLC) flakes have potential in a particle display intended for electronic paper. They promise full color capabilities, with bright saturated colors without use of color filters and polarizers, on rigid or flexible substrates. A PCLC flake display could consume less power than some current particle display technologies.; This work addresses some of the issues for improvement of the PCLC flake technology. Manufacturing of shaped PCLC flakes which give a uniform and reproducible electro-optic behavior in different host fluids under an applied electric field is shown here. The earlier flake work is extended to new PCLC materials as well as new hosts, tested in both AC and DC regimes. The Maxwell-Wagner polarization as the main mechanism which drives the flake motion in an electric field is confirmed for shaped flakes. The key material properties (of the flakes and of the host) that contribute most to flake reorientation and relaxation time are described here. Flake and/or host fluid conductivity is shown to be the most easily adjusted property for reducing response time and for extending response to the DC regime. The origin of ions/charges responsible for the flake motion in an electric field is shown to come from the flakes themselves, the host fluid and the ITO substrates. Modifications in material properties of the flake and host are made by doping, and their performance is compared to that for neat flakes in neat hosts. An extended model for reorientation time is developed that includes a gravity term. This extended model is shown to agree well with most experimental results, without the use of any adjustable parameters. |
