Transient pressure changes in Donnan systems displaced from equilibrium.

PRESSURE gradients at interfaces of porous membranes can be caused by two factors: (1) discrete changes in concentrations of particles which are excluded from the aqueous pores because of their size, and (2) electrical stresses which are caused by the action of an electric field on the charged particles at the membrane–solution boundary (A.I., theoretical results to be published elsewhere). Only the first factor is important in neutral pore-containing membranes; the second operates at the boundary of charged pores, that is, in ion exchange membranes.