REVERSIBLE DIFFUSION-CONTROLLED REACTIONS BETWEEN 2 SPECIES IN A FLUID

A model suspension of diffusing spherical particles with an internal d egree of freedom taking two discrete values, or equivalently a two-com ponent suspension with reactions between species, is studied. The inte rnal degrees of freedom of neighboring particles are coupled by an Isi ng type interaction of short range. The dynamics of the Ising variable s is described by a master operator of Glauber form. On a macroscopic level small deviations of the two densities from their equilibrium ave rages obey transport equations with memory character. The memory kerne l is derived from the Mori formalism. The two-body contribution to the cluster expansion of the memory function is obtained analytically at zero wavevector. The spectrum of the memory function shows a marked de pendence on the presence or absence of an external field, the ratio of time scales for transitions between states and for translational diff usion, and on the antiferromagnetic or ferromagnetic character of the Ising interaction. (C) 1997 American Institute of Physics.