Probing the Dielectric Response of Polyurethane/Alumina Nanocomposites

The dielectric properties of polyurethane (PUR) latex-boehmite alumina nanocomposites were investigated by means of broadband dielectric spectroscopy in the temperature range -100 degrees C to 70 degrees C. The concentration of the filler (alumina) was kept constant at 10 phr for all specimens, whereas the mean particle diameter (namely 220, 90, and 25 nm) of the incorporated nanoparticles varied accordingly. For reasons of comparison, pure PUR was also examined. Four distinct relaxation modes were recorded in the spectra of all systems. They were attributed to interfacial polarization, glass transition (alpha-relaxation), local motions of polar side groups, and chain segments (beta-relaxation and gamma-relaxation). All four relaxation processes exhibit a symmetric distribution of relaxation times, which in the case of interfacial polarization, becomes narrower. The intensity of interfacial polarization increases with the reduction of the mean particle diameter indicating enhanced interfacial area. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2346-2354, 2010