**5. Polymer-stabilized liquid crystal**

Polymer-stabilized liquid crystal is a thin composite film prepared from the homogenous mixture of LC and monomer. Typically, the monomer concentration in PSLC is less than 10% of the total weight. The small amount of monomer is used to stabilize/lock the oriented LC structure at different optical states and to reduce the switching time and operating voltage [73]. The homogenous mixture of LC and polymer is prepared and filled into the prefabricated cells made of transparent ITOcoated electrodes for photopolymerization using PIPS technique [51]. For improved display performance, LCs should be homogenously and uniformly aligned inside the cell. To control the orientation of LC, the inner face of electrodes is coated with a transparent polymeric material (generally PI) followed by baking and rubbing [53]. A thin layer of PI is known for its excellent strong and outstanding heat, mechanical, and chemical resistivity [53]. The mechanical treatment such as unidirectional rubbing modifies surface topography by breaking the symmetry and creating linear microgrooves on the polymer surface [48, 54, 56]. The rubbing direction on one ITO plate is 0° or 90° with respect to the other depending upon the parallel/antiparallel or twisted mode, respectively [55, 74]. This induced anisotropic surface diffuses monomer molecules preferentially along the rubbing direction. Due to strong interaction and anchoring between LC and monomer, the polymer network formed during/after polymerization keeps the LC director in a definite direction [75]. Along with the surface alignment layer, the configuration and orientation of LC can also be controlled by application of external field and/or temperature during photopolymerization. Even low electric field is sufficient to align the LC director along the field by fixing torque on it. After establishing the proper combination of surface treatment and applied field, the sample is irradiated by ultraviolet (UV) light to induce photopolymerization to obtain the desired texture. Since the monomer concentration is very small, a continuous LC texture along with interconnected, interpenetrating and mitigated polymer network can be obtained after polymerization [61, 76–78] as shown in **Figure 20**.

Because of application of electric field during photopolymerization, oriented LC domains are formed. Also, this controlled alignment of the LC molecules between polymer networks has significant effect on the transmittance, absorbance, response time, and dielectric properties of PSLC films [79].

**Figure 20.** *Polymer stabilized liquid crystal.*

*An Overview of Polymer-Dispersed Liquid Crystal Composite Films and Their Applications DOI: http://dx.doi.org/10.5772/intechopen.91889*
