morphology than in the PS one because in the
former, the hard segments are dispersed throughout
the material instead of forming clusters. Therefore,
the PM morphology is likely to contain a larger
amount of charges, resulting in a higher electrostrictive
response for this type of samples. Our data
were in agreement with this prediction and, therefore,
tended to reinforce the validity of the suggested
space– charge theory. However, to definitely
establish the validity of this theory, a more quantitative
study should be undertaken, where the relative
amount of space charges is evaluated and used
to estimate the magnitude of the resulting nonuniform
electric field. The field nonuniformity should
also be taken into account in subsequent attempts to
model polyurethane electrostriction, as this may be
one of the missing key features of the current macroscopic
models.