EFFECTS OF POLYMER-SOLUTIONS ON COLLOID STABILITY

Some theoretical properties of a semidilute polymer solution (in a good solvent) near a repulsive wall (no adsorption) are discussed. (i) Near a single wall, the existence of a depletion layer (where the concentration is strongly reduced) with thickness equal to the correlation length zeta (c) is predicted. Scaling laws are obtained for the concentration c//s at the first layer as a function of the bulk concentratiuon c, and for the concentration profile c(z) at distance z from the wall. (ii) When two parallel walls are separated by a slab of polymer solution (thickness d), there is an attractive interaction between the plates. The range of the attraction is ca. 3 zeta (c) and can be varied by suitable choice of concentration. It may lead to destabilization of certain colloidal systems.