Time-dependent thermodynamics applied to flow of suspensions and polymer melts

Abstract

Rheological behavior has been treated in terms of the energy flow by coupling it with deformation and flow of material. The method follows time-dependent thermodynamics, which is different from Prigogine’s irreversible thermodynamics. We have examined the rate of energy production with particular attention to the physical meaning of the sign of the rate. Just as the sign of energy indicates in thermodynamics, whether or not the reaction is spontaneous, the sign of the rate indicates in time-dependent thermodynamics, whether or not the reaction is stable. In the stable region, the reaction is reversible. For a change from stable region to an unstable region, there is a discontinuity. Then, there is a pseudo-stable region, where a partial reversibility may be observed. This behavior involves yielding, which leads to fracture, like that seen in a longtime creep failure of a solid material. We have examined non-Newtonian flow of polyvinyl chloride plastisol, steady-state flow of high-density polyethylene melts, and its stress growth toward steady state.