Smectic A compositions for use in optical devices

Abstract

A liquid crystal smectic A composition which can be brought into a first stable state (left hand block in Figure 4) and at least one second stable state (Fig. 4), the composition is more disordered in at least one second stable state than in the first state. The radiation transfer properties of the first state and the second state are different. The composition comprises: (A) a liquid crystal material having a positive dielectric anisotropy and, when in a first state, a uniformly aligned smectic A structure; (B) an ionic dopant, which is present in the liquid crystal material Negative conductivity anisotropy is provided in such that when subjected to an electric field that causes the dopant to migrate through the composition, the dopant is capable of disrupting the smectic A structure of the first state, thereby causing the composition to switch to the at least one A second state, and (C) optically anisotropic pigment particles, which have positive dielectric anisotropy, are dispersed in the composition, and the maximum size of the pigment particles is in the range of 10 nm to 1 μm. The composition, when in a first, relatively steady state, is capable of undergoing smectic dynamic scattering due to electrohydrodynamic instability under the influence of a sufficiently low frequency alternating electric field, thereby disordering liquid crystal and pigment particles, and thereby preventing Pigment particles clumped together. The composition is suitable for use in displays, and is especially resistant to degradation due to ambient light, and can therefore be used in outdoor applications.

Description

technical field

[0001] The present invention relates to liquid crystal compositions having a smectic A structure, cells containing such compositions sandwiched between a pair of electrodes, optical devices containing one or more cells, and methods for switching the composition by applying an electric field to the composition method of optical properties. Background technique

[0002] Smectic liquid crystals (LC) are materials that, when cooled from an isotropic (liquid) phase and before solidification, can form a liquid crystal phase with a layered structure in which liquid crystal molecules display various morphologies within each layer. The various morphologies give rise to many different smectic phases designated by the letters A, B, C, etc., the most common smectic phase being smectic A (SmA). The SmA phase has LC molecules that are orthogonal to the layer but randomly distributed within the layer, thus, it is one of the least ordered smectic phases. X-ray studies have...

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