Improvement of electrostrictive properties of a polyether-based polyurethane elastomer filled with conductive carbon black

The electrostrictive properties of a polyether-based polyurethane elastomer and its corresponding composites filled with conductive carbon black (CB) were studied by measuring the thickness strain S-Z induced by external electric fields E. For films with thicknesses of approximately 50 mu m, the apparent electrostrictive coefficient M was measured at low electric fields, E <= 4 V/mu m, and different CB contents (up to a volume fraction of 2%). Dielectric measurements in AC mode were performed in order to determine the percolation threshold f(c), which was 1.25 v%. This optimal volume fraction yielded a remarkable threefold increase in M, associated with an increase of the dielectric constant by a factor 7, in comparison with pure PU. This enhancement of the electric field-induced strain and apparent electrostriction was mainly triggered by an increase of the dielectric constant, even if the intrinsic electrostriction coefficient Q was decreased. The nanocomposites thus seem to be very attractive for low-frequency electromechanical applications. Above f(c), their conductivity was raised and their electrostrictive activity lost. Finally, there is a good agreement between the experimentally determined dependence on the CB content of the M coefficient and the theoretical estimation calculated from dielectric and mechanical measurements. (C) 2011 Elsevier Ltd. All rights reserved.