On the invariance of Onsager's reciprocal relations in the thermodynamic theory of dielectric relaxation phenomena
In some previous papers a theory for dielectric relaxation phenomena in polarizable media was developed by introducing a set of thermodynamic internal variables identified with the n + 1 partial specific polarization vectors p( k) ( k = 0, 1, 2, …, n) in which the total specific polarization vector p can be split. Moreover, it was shown that the entropy production can be characterized also if a set of n “hidden” vectorial parameters Z(λ) ( k = 1, 2, …, n), related to the p( k) ( k = 1, 2, …, n) by vector-valued transformation laws, is assumed as new thermodynamic variables. Of course two forms for the balance equation for the entropy can be deduced and two formalisms for the development of the theory can be derived. In the present paper we point out that these two formalisms are equivalent and we show that the corresponding Onsager reciprocal relations for the phenomenological coefficients are invariant under the vector-valued transformations between the two sets of internal variables.