Non-equilibrium Thermodynamics and Rheology

Abstract

Local-equilibrium thermodynamics assumes that the equations of state retain the same form out of equilibrium as in equilibrium, but with a local meaning (Prigogine 1961; De Groot and Mazur 1962; Gyarmati 1970). According to this point of view, there is not strictly any especial thermodynamic features characteristic of flowing fluids, since the flow does not change the equations of state, though it may modify the transport equations. This approach is insufficient to deal with systems with internal degrees of freedom, in which case the flow may influence the thermodynamic equations of state through its action on such internal variables. In such occasions (Meixner 1949, 1954; Verhas 1997; Lhuillier and Ouibrahim 1980; Maugin and Drouot 1983; Maugin and Muschik 1994a, b; Maugin 1999) one includes in the set of thermodynamic variables some internal variables describing the relevant details of the microstructure of the system, such as, for instance, the polymeric configuration.