One proposed mechanism to explain electrostriction
relies on the PS morphology of the polyurethane:10,11
because this structure corresponds to hard-segment
domains embedded in a stretched matrix of soft segments,
the explanation for the observed large strains
was the relaxation (by crystallization) of the matrix
under electric field. It was to test this hypothesis (and
also to assess the general effects of the polymer structure
on electrostriction) that samples with the PS and
PM structures were synthesized at NSWC. Because
both types of samples had a measurable electrostrictive
response, phase separation alone could not completely
account for the phenomenon. In fact, results on
the PM 2000 material indicated a larger electrostrictive
activity in these materials than in the ones with the PS
structure. Therefore, we conclude that the proposed
mechanism based on phase separation cannot be validated
as solely responsible for electrostriction (although
we have not established that it does not contribute
at all) and that the latter is actually enhanced
by phase mixing.