Polymer networks introduced in liquid crystal matrix greatly influence the behavior of surrounding liquid crystal. Based on their morphology there are two main types of liquid crystal-polymer composites. The polymer dispersed liquid crystal (PDLC) represents one end of the spectrum where a high concentration (grater than 20%) of polymer is used to create a macroscopically phase separated system of liquid crystal and polymer. The addition of small amounts of polymer (few percents) to a liquid crystal host falls into regime of polymer stabilization. Though the concentration may by small, the resultant effect is usually large. Some notable applications of polymer stabilization to LCD technology include: the lowering of threshold in TN and STN displays (link to: P.J.Bos, J.Rahman, and J.W.Doane, SID ‘93 Tech.Digest, 887, 1993), the elimination of stripes in STN displays, the stabilization of the BCT displays (link to: J.Li, J.R.Kelly, C.D.Hoke, and P.J.Bos, Asia Dysplay ’95, 251, 1995), the stabilization of ferroelectric LCD against mechanical stresses1, and to enable normal and reverse mode cholesteric displays2. In recent years, new types of monomer and a better understanding of how they behave has opened the door to previously unconsidered applications of polymer stabilization. This includes creation of spatially separated by polymer walls pixels and recent its application to solve long term stability in BCT (link).
Related papers:
[1] D.-K. Yang, J.L. West, L.-C. Chien, J.W. Doane, J. Appl. Phys., 76, 1331 (1994).
[2] J.Pris, B. Martin, J.W.Doane, Mol. Cryst. Liq. Cryst., 264, 2176 (1995).