THERMODYNAMIC CONSIDERATIONS ON THE ELECTRORHEOLOGY OF NONCOLLOIDAL SUSPENSIONS

Thermodynamics provides a convenient framework to analyze the electror heology of suspensions of non-Brownian, noncolloidal particles in Newt onian carriers. Aided by simple constitutive relations Linking suspens ion architecture to its electrical response, we examine the evolution of the microstructure upon cessation of flow and the linear-elastic be havior in the preyield region. In the case where the particles and the fluid are both nonconducting, a rigorous proof can be worked out to s how that, upon cessation of flow, the suspension microstructure will e volve towards a ''pillared'' configuration, whereby chains of particle s spanning the flow gap are formed. Also, a maximum in the linear-elas tic shear modulus as a function of solid concentration is predicted in this case, under certain conditions. For finite solid and carrier con ductivities, where Maxwell-Wagner-Sillar polarization can occur, the r esults are less rigorous; although some necessary conditions for stabi lity of the pillared structure can still be inferred. (C) 1996 Society of Rheology.