Modes for Liquid Crystal Devices

Abstract

The first observation of a liquid crystalline phenomenon was made in 1888 by the Austrian botanist Reinitzer, in Graz. He noticed an opaque appearance in liquid cholesterol benzoate upon melting which turned into the common transparent liquid state when further increasing temperature. Only decades later it was realized that liquid crystals are not suspended solid-state microcrystals but represent a novel class of materials exhibiting long-range molecular order within their liquid crystalline temperature range. As a consequence of long-range order, liquid crystals exhibit unique anisotropic optical, dielectric, and mechanical properties. In 1918 Bjornstahl (Ann. Phys. (Leipzig) 56:161, 1918), Uppsala, published the first study of an electro-optical liquid crystal effect. Upon current flow through a thin, negative dielectric liquid crystal (LC) film of p-azoxyanisole, he observed light scattering. In 1935 Zwetkoff (C. R. Acad. Sci. USSR 4:131 1935) reported analogous results in sandwich cells using also p-azoxyanisole, i.e., the standard LC used by virtually all scientists between 1900 and 1960. In the mid-1960s industrial research groups in the United States and in Europe became interested in liquid crystals for potential electronic display applications. At that time the few compounds known to exhibit liquid crystallinity were unstable, and their melting temperatures were typically far above room temperature and/or extending over much too narrow temperature ranges for practical use. Only few of the numerous anisotropic optical, mechanical, and dielectric properties of liquid crystals (LCs) were known, and reliable experimental means for their investigation had hardly been developed (Schadt, Jpn. J. Appl. Phys. 48:1 2009, Schadt, Naturwissenschaftliche Rundschau 741:117 2010, Schadt, J. European Acad. Sci. 1:1 2011). Correlations between molecular functional groups, display-relevant LC material properties, and electro-optical properties which are prerequisite for advancing LC materials and LCDs hardly existed.