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Liquid Crystals

Dielectric Properties of a Polymer-Dispersed Liquid Crystal Film

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Pages 75-81 | Received 14 Dec 1990, Accepted 20 Jun 1991, Published online: 24 Sep 2006
 

Abstract

Dielectric properties of a polymer-dispersed liquid crystal (PDLC) film comprising of liquid crystal, octyl cyanobiphenyl (K-24) and polymethyl methacrylate (PMMA) are reported as a function of frequency (100 Hz-1.0 MHz) in the temperature range of 25°C to 45°C. A dielectric dispersion in the low frequency region (∼1 KHz) was observed while no such dispersion was seen in either pure PMMA or pure K-24. The dispersion is due to Maxwell-Wagner polarization mechanisms. The temperature variation studies show (i) a discontinuous jump in the dielectric permittivity at the nematic-isotropic and smecticnematic transitions and (ii) also a lowering of the transition temperatures, suggesting some contamination of liquid crystal by the polymer. Simple dielectric theories of composites have been applied to estimate the molecular alignment of liquid crystal (LC) molecules inside the micro-droplets.

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