In the study of thermoelastic actuation of dielectric elastomer, we can write the Helmholtz free-energy as a function of stretch ratio, nominal electric displacement and temperature (T).
The entropy (S) is the negative partial differential coefficient of W with respect of temperature (T). And we can see the change of S is due to three components: deformation, heat conduction and polarization. In an isothermal state, the deformation part has been fully investigated by Arruda and Boyce in 1993, but the polarization-induced entropy (Sp) has not been clearly stated.
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