György Bánhegyi

Structure and properties of polyurethane–silica nanocomposites

Nanocomposites with different concentrations of nanofiller were prepared by adding nanosilica filler to the single-phase polyurethane matrix. A control series was prepared with the same concentrations of micron-size silica. The nanosilica filler was amorphous, giving composites with the polyurethane that were transparent at all concentrations. The nanocomposites displayed higher strength and elongation at break but lower density, modulus, and hardness than the corresponding micron-size silica-filled polyurethanes. Although the nanosilica showed a stronger interaction with the matrix, there were no dramatic differences in the dielectric behavior between the two series of composites.

Applied Dielectric Spectroscopy of Polymeric Composites

Abstract In this article a theoretical background for understanding dielectric phenomena in heterogeneous polymeric composites is presented, and the application of these principles to practical problems is illustrated by experimental examples. First a short overview of the existing theoretical mixing formulae is given, the differences in these approaches are discussed, and the areas of application are indicated. Conditions for the appearance of an interfacial relaxation process are delineated; limitations of the theories are given. Experimental examples include immiscible polymer blends, mineral-filled polyolefins, thermoset composites, and conductive composites. In the first example, AC dielectric spectroscopy is used to monitor the phase separation process and to evaluate interactions between the separated phases. In the second example, the effect of filler permittivity, volume fraction, and surface treatment is discussed with respect to the AC and DC dielectric properties. It is shown that in mineral-f...