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Liquid Crystals Beyond Displays: Chemistry, Physics, and Applications by Quan Li

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Chapter 16

Polymer Stabilized Cholesteric Liquid Crystal for Switchable Windows

Deng-Ke Yang

Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, OH, USA

16.1 Introduction

Liquid crystals (LCs) have been used to make switchable windows. The state-of-the-art technologies are polymer dispersed liquid crystals (PDLCs) and polymer stabilized cholesteric texture (PSCT) light shutters [1–4], which were developed at Kent State University. In PDLCs, liquid crystals exist in micron size droplets which are dispersed in an isotropic polymer. The concentration of the polymer is comparable to that of the liquid crystal. The polymer forms a continuous medium and the liquid crystal droplets are isolated from one another. The rod-like liquid crystal exhibits optical birefringence: ordinary refractive index no for light polarized perpendicular to the liquid crystal and extraordinary refractive index ne for light polarized parallel to the liquid crystal. The polymer is optically isotropic with the refractive index nP. The materials are chosen in such a way that nP = no < ne. In the absence of an electric field, either the droplet director orients randomly throughout the PDLCs or the liquid crystal director inside the droplet orients in all directions as shown in Figure 16.1a. When light propagates through a LC droplet, the encountered effective refractive index neff, which is between no and ne, is different from the refractive index nP of the polymer. ...

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