ON MULTICOMPONENT, MULTIPHASE THERMOMECHANICS WITH INTERFACES

The thermomechanicms of a multiphase multicomponent mixture are develo ped in the spirit of modern continuum physics. A new axiom of constitu tion, ''equipresence of constituents'', is stated and employed to obta in macroscale equations of constitution which are consistent with thei r microscale counterparts. Here we are assuming a scale separation whe rein the classical microscale theory of mixtures applies within each p hase and interface, and a hybrid theory of mixtures, which is a homoge nization of the microscale mixture theory over phases and interfaces, applies at the macroscale. We thus postulate the existence of a two-sc ale hierarchy of overlaying continua. Such scale separation is common to many types of porous media. Exploitation of the entropy inequality in the sense of Coleman and Noll and application of equilibrium constr aints produces a complex list of functional relations forming a macros cale theory of constitution. In a three-phase system linearization of several of these relations produces novel analogs of Fick's first law of diffusion and Darcy's law of fluid transport in deforming porous me dia. These analogs of Fick's and Darcy's laws are significantly differ ent from their traditional froms in that they contain an ''interaction potential''. The authors feel that the contribution fo the interactio n potential to fluid flow dynamics could be of crucial importance in s welling and shrinking colloidal systems. Another especially important consequence of the theory of constitution is the development of the ex perimentally observed exponential relation between disjoining (swellin g) pressure and the pore width in a smectitic clay-water system. This relation cannot be developed using classical Gibbsian thermostatics.