Consequences of non-uniqueness in the free energy of materials with memory

It is well known that for many materials with memory, the free energy and e ntropy are not uniquely defined. Such arbitrariness cannot extend to direct ly measurable quantities. The consequences of this requirement are explored in the work reported here both in a general framework and within the conte xt of a quadratic model of free energy. In the latter case, it is shown tha t a quantity, which reduces in the linear isothermal case to the time-depen dent part of the relaxation function, must be proportional to the absolute temperature. (C) 2000 Elsevier Science Ltd. All rights reserved.