The electro-optical effect of size polydispersity in polymer-dispersed liquid-crystal (PDLC) films is investigated. Liquid crystal (LC) droplets of different sizes require different electric field amplitudes for director reorientation, which will produce a mismatch of effective refractive indices. This, in turn, will produce an increase in interdroplet scattering (i.e., decrease in the direct transmitted light) within a specific range of electric field amplitudes. We propose a phenomenological “two-size” model describing this enhanced “pseudo-off-state” achieved under application of an electrical field and present validation experiments. Our approach may be used to get more insight into the transmittance behavior of PDLCs affecting the contrast ratio.
We present a novel electric-field and voltage sensor based on the electro-optical properties of polymer-dispersed liquid-crystals (PDLCs). In principle, the transmittance of PDLCs is a nonlinear function of the applied electrical field. To measure an AC field we superposed to it a known DC field. This allowed us to achieve linearization of the PDLC response and to measure transmittance changes independently of the light-intensity level variations. Validation experiments are presented.
In this article, the light transmission process in single- and double-layered polymer-dispersed liquid-crystal (PDLC) cells and its relevance for contrast ratio calculations have been discussed. Double-layered cells consist of two PDLC films with a common central wall. We demonstrate theoretically and experimentally that the contrast ratio of double-layered cells is larger than the one of a single PDLC film, but in general, it is not the product of the contrast ratios of the individual films, contrary to the result obtained neglecting multiple scattered light. The same result holds for a single film working in reflective mode. Our results may be potentially relevant for display applications.
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