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 fc
, 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