In this paper we discuss the optical reflective properties of single and multidomain cholesteric liquid crystals both experimentally and theoretically. The multidomain system has been prepared by dispersing a low concentration of polymer in a cholesteric liquid crystal. This results in a (passive) bistable colorful reflective display. Here we discuss the role of the polymer in altering the reflective properties in regard to their spectra and viewing characteristics. Theoretically we o6'er an application of the well known Berreman method [J. Opt. Soc. Am. 62, 502 (1972)] suitable for systems composed of an ensemble of uncorrelated domains, each of which is composed of the same dielectric anisotropy, however with its own local orientation. Using this technique the reflective properties of a cholesteric liquid crystal possessing a distribution in the orientation of the helix axes are simulated. We furthermore illustrate how a small fluctuation in the pitch from one domain to another significantly reduces any interference fringes. From these simulations we will show how experimentally by using a polymer network one may control the extent to which the orientation of the helix axes are distributed.PACS number(s): 61.30.v
A small Plinian eruption of the Nevado del Ruiz volcano in Colombia ejected 3.5 x 10(10) kilograms of mixed dacite and andesite tephra on 13 November 1985, with a maximum column height of 31 kilometers above sea level. Small pyroclastic flows and surges, generated during the initial stage of the eruption, caused surface melting of approximately 10% of the volcano's ice cap, leading to meltwater floods. The erosive floods incorporated soils and loose sediments from the volcano's flanks and developed into lahars, which claimed at least 25,000 lives.
Optical birefringence patterns of nematic liquid crystals constrained to supramicrometer capillary tubes with homeotropic anchoring are sensitive to the detailed bulk elastic properties of the nematic material. The bend-to-splay elastic constant ratio (K33/K11) is estimated by comparing the escaped-radial nematic director field observed via optical polarizing microscopy to simulated textures predicted by the Frank elastic theory.
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