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Infrared Microscopic Imaging of the Diffusion of Liquid Crystals into Thermoplastics

Published online by Cambridge University Press:  02 July 2020

Bentley G. Wall
Affiliation:
Department of Macromolecular Science, Case Western Reserve University, Cleveland, OH44106
Chris M. Snively
Affiliation:
Department of Macromolecular Science, Case Western Reserve University, Cleveland, OH44106
Jack L. Koenig
Affiliation:
Department of Macromolecular Science, Case Western Reserve University, Cleveland, OH44106
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Thermoplastic polymer/liquid crystal systems have found application in the generation of display devices known as thermoplastic, polymer dispersed liquid crystals (PDLCs). These systems take advantage of the beneficial properties of both components to generate a device that has unique optical properties. The liquid crystal is dielectric and responds to an electric field. The polymer confines the liquid crystal so that the cells are closed. The two components are melted together until they are miscible. At lower temperatures, the two components phase separate. The liquid crystal component is the minor phase and takes the form of many tiny droplets contained within the major-phase, polymer matrix. An application of an electric field across these systems causes the liquid crystal within the droplets to align with the field. The systems are engineered such that when this alignment occurs there is no refractive index difference between the liquid crystal in the droplets and the polymer matrix, thus, the cells appear optically transparent. When there is no field applied, the liquid crystals in each droplet are aligned without respect to a general direction according to the surface energetics of each droplet/polymer interface. When this is the case, there is a refractive index mismatch between the droplets and the polymer and the cells are opaque. Research of these systems is aimed at improving the optical properties in order to facilitate the manufacturing of improved devices utilizing this technology. Because these systems are generated by a diffusion-controlled, phase separation process, understanding the relevant parameters, particularly the diffusion coefficients, should enable the manufacturing processes of these systems to be controlled more efficiently, generating improved optical properties.

Type
Optical Microanalysis
Copyright
Copyright © Microscopy Society of America 1997

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