We have investigated two approaches to improving the electro-optic performance of polymer dispersed liquid crystal (PDLC) films. One involves using a partially fluorinated epoxy based thermoset to serve as the PDLC binding matrix. Results indicate that this causes an enhanced phase separation of the liquid crystal which leads to significant changes in the contrast ratio and fall time of a PDLC film. The other approach involves using duel frequencies to enhance the electro-optic performance of another type of PDLC film. Studies suggest that the hysteresis effect can be minimized and the overall control of the electro-optic response can be greatly increased by adding a second high frequency component to the PDLC driving voltage.
Several different types of polymer dispersed liquid crystal (PDLC) systems have been developed in recent years. The transmission characteristics of each type depend on the materials used, the method of construction, and the addressing technique used to drive the system. Greater control over the transmittance response as a function of time is important for many display operations. The effect of using dual-frequency addressing and pulsed mode dual frequency addressing in controlling the transmittance response of one type of PDLC film has been investigated. The results suggest that the gray scale inconsistency as well as the hysteresis effect can be reduced by utilizing the frequency dependence of the dielectric anisotropy of the liquid crystal.
Generally one type of polymer is used in the construction of polymer dispersed liquid crystal (PDLC) films. The authors tested the effect of incorporating an additional fluoropolymer in varying percentages on the electro-optic performance of PDLC films based on poly(methyl methacrylate). Compared to samples made from a single polymer, several correlations are noted, including a decrease in liquid crystal fall-time, an increase in rise-time, and an increase in the threshold voltage (Vt).
A conducting PRIZ device is fabricated and shown to exhibit the
unique image processing features of edge detection, directional spatial
filtering, and dynamic image selection. The active element is single
crystal bismuth silicon oxide (Bi12SiO20 or BSO) . Auger electron
spectroscopy (AES) and neutron activation analysis (NAA) techniques
were applied to BSO to identify the impurities which contribute to the
device operation.
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