NONEQUILIBRIUM SWELLING-PRESSURE AND CAPILLARY-PRESSURE RELATIONS FORCOLLOIDAL SYSTEMS

In a previous article (Achanta et al., Int. J. Eng. Sci., in press) th e authors developed a constitutive theory for a multiphase, multicompo nent mixture with interfaces. Here that theory is exploited for both e quilibrium and nonequilibrium situations to develop functional forms f or swelling pressure (or disjoining pressure) and capillary pressure i n colloidal systems. The swelling pressure is found to be the pressure difference between the interfacial and bulk phases only at equilibriu m. For the general nonequilibrium case, using a linear theory, an extr a term in the material derivative of volume fraction is found in the s welling relationship. This nonequilibrium relationship is consistent w ith the intuitive postulate of Thomas and Windle (Polymer 23, 529, 198 2), who used a similar relationship to explain viscous swelling of pol ymers under osmotic stresses. The equilibrium swelling pressure is sho wn to reduce to the exponential form of Low (Langmuir 3, 18, 1987) und er special conditions. A similar relation is developed for capillary p ressure, which is consistent with an earlier derivation of Hassanizade h and Gray (Water Resour. Res. 29, 3389, 1993). (C) 1994 Academic Pres s, Inc.