Effect of electrical field on dipoles in polymer composites



Orientation of two bipolar compounds embedded in polymer composites was studied. Poly(methyl methacrylate) (PMMA) dissolved in acetone was doped with a cobaltborane derivative of 1,2-dimethylimidazole and polystyrene (PS) dissolved in toluene was doped with the 3-(1,2-dimethyl imidazole)-borane. To orient the dipoles, the composites were exposed to external electrical field: PMMA composite at the temperature of glass transition (Tg) and PS composite during evaporation of the toluene solvent. The degree of dipole orientation was estimated by the change in relative permittivity (ε) of the resulting composite film. The dependence of the ε on the temperature, frequency, voltage, and dipole concentration was studied. It was found that the dipole's distribution in the composite film was not homogenous. At the Tg, the dipoles in PMMA became oriented by external direct electrical field and the orientation was conserved after cooling to lower temperatures. In a PS-based composite, the significant permittivity increase was observed already at low-dopant concentrations. The dipole orientation achieved during solvent evaporation was also permanent and the composite permittivity was an increasing function of the film thickness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 40–45, 2004