Non-equilibrium thermodynamics of membrane processes

Abstract

By applying the theory of non-equilibrium thermodynamics to membrane processes it is found that the action of a membrane in a system containing n components is completely characterized by 1/2n(n + 1) thermodynamical constants. In measurements of transference numbers, membrane potentials and electrokinetic constants, a set of phenomenological constants can be determined from which, if sufficient independent data are obtained, the thermodynamical constants may be computed. The relations between phenomenological and thermodynamical constants are given. Also a number of relations between different phenomenological constants is given, which must hold independently of any model of the action of the membrane. Some of these relations, such as Nernst's equation for the diffusion potential and some relations between electrokinetic constants have been derived before by quasi-thermodynamical reasonings or from calculations on models. Others, such as the relation between mechanical and electrical transference numbers, the relation between these and the electro-osmotic permeability, and the expression for the osmotic pressure in terms of mechanical transference numbers, are new. A discussion of the meaning of current model theories in terms of our thermodynamical treatment is given.