 | Droplet Configuration |  |
Polymer-dispersed liquid crystals hold potential for a variety of electro-optic applications ranging from displays to light shutters. Below, we illustrate their applications as electro-optic light shutters in the construction of privacy windows.
PDLC windows are based on the ability of the nematic director of the liquid crystal droplets to align under an electric field as discussed in the previous section (also see Electric and Magnetic Field Effects). In a typical application, a thin PDLC film (about 25 microns thick) is deposited between clear plastic covers. The plastic substrates are coated with a very thin layer of a conducting material known as indium tin oxide (ITO). The following diagram shows a simple PDLC cell.
Transmission of light through a PDLC window depends primarily on scattering which in turn depends on the difference in refractive index between droplets and their environment. In the case of high droplet density, the environment consists mainly of other droplets, which makes the relative orientation of their directors an important factor. The droplets are anisotropic with the index of refraction parallel to the director different from that perpendicular to it.
In the field OFF, the random array of droplet orientation provides significant differences in indices and hence strong scattering. In this state, the cell appears opaque. When a voltage is applied, however, the director of the individual droplets align with the field. There is now little difference in refractive index for neighboring droplets, and the cell appears transparent.
| | Droplet Configuration | |