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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 3: Liquid Crystals and Polar Fluids

CPP 3.2: Vortrag

Montag, 25. Februar 2008, 10:15–10:30, C 264

Dielectric relaxation behavior of nematic liquid crystals dispersed in a ferroelectric polymer — •Lakshmi Meena Ganesan, Axel Mellinger, Peter Frübing, Werner Werges, and Reimund Gerhard — Department of Physics, University of Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany

Polymer-dispersed liquid crystals (PDLCs) are a class of materials that consists of micrometer-sized liquid-crystal (LC) droplets embedded in a polymer matrix. Here, ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) (65/35 mol%) was used as the matrix polymer, since the electric field generated by the piezo- or pyro-electric effect of the matrix material could potentially be used to switch the director of the LC. In the absence of an external electric field, the nematic molecules at the interface are oriented spontaneously at a specific angle. The phenomenon of orienting the LC molecules at an interface is called anchoring. By application of an electric field, the nematic molecules can be oriented along the field direction. If the perpendicular refractive index of the liquid crystal matches the refractive index of the polymer matrix, the optical transmission of the PDLC film increases. The anchoring effect can be studied using dielectric relaxation spectroscopy. Two dispersion regions are observed in the dielectric spectra of the pure P(VDF-TrFE) film. They are related to the glass transition and to a charge-carrier relaxation. In PDLC films containing 10 wt% of LC, an additional, bias-field-dependent relaxation peak is found that can be attributed to the motion of LC molecules.