Maxwell stress contribution
The results presented in Table I reveal that the deformations
due to the Maxwell stress effect accounted for
less than 15% of the total strains. This is an important
finding that proved that most of the electromechanical
activity in the polyurethanes stemmed from intrinsic
electrostriction. This was in contrast with the findings
of other researchers that claim that Maxwell stress is
responsible for approximately 50% of the polyurethane
strain response.2,3 This discrepancy between our
results and theirs is most likely due to the fact that
they used electroded samples and, therefore, measured
a constrained response (the Maxwell contribution
is calculated and is independent of the measuring
technique). On the basis of the values that we obtained,
it is our conclusion that the electrostatic attraction
is in fact a minor factor in the mechanical response
of a polyurethane film to an applied electric
field.