Inherent and incredible properties of liquid crystals (LC) such as optical and dielectric anisotropy make them special candidates for flat-panel display devices; bi-stable reflective displays; high-definition spatial light modulators; switchable windows; haze-free normal- and reverse-mode light shutter devices; projectors; optical, thermal and strain sensors; tuneable lenses; etc. Non-linear response of LC material to the applied electric field is very useful in the above-mentioned applications. When a low molecular weight LC material is doped in a high molecular weight polymer matrix to obtain polymer-dispersed liquid crystal (PDLC) films, it offers flexibility and mechanical strength (structural stabilization) to the composite films—PDLC devices. Depending upon the concentration of monomer/polymer, these composite films are classified as polymer-stabilized liquid crystal (PSLC), PDLC and holographic PDLC (HPDLC) films. Depending upon the process conditions, we get phase-separated randomly dispersed micron-sized LC droplets in a continuous polymer matrix. These nematic LC droplets exhibit light scattering transmission properties depending on their orientation, which can be controlled by external electric field. This chapter gives deep insight about operating principle, phase separation techniques involved, alignment of LC and controlling LC droplet morphology of PDLC films to obtain desired properties. In order to improve the optical efficiency and to obtain the desired result from PDLC films, various guest entities such as dye and nanomaterials are doped in the host LC material. This chapter also accounts for various possible LC dopants desired for improving the electro-optic (EO) and dielectric properties of PDLC devices. Various applications of PDLC composite films are also described in this chapter.
Part of the book: Liquid Crystals and Display Technology