Surface forces in athermal polymer solutions

Forces between planar surfaces immersed in a polymer solution are compared with those of the pure solvent in order to establish the effect of adding polymer. We use an off-lattice model consisting of hard-sphere polymers in a hard sphere (athermal solvent). The model is analyzed using a recently introduced density-functional theory. Due to the typically high density of liquids, the forces in both solution and solvent are oscillatory, leading to a more complicated picture than the classical description of polymer depletion forces. Rather than a well-defined attractive depletion regime in the surface forces, the effect of polymers is better described as a damping of the oscillatory force in the pure solvent. It is only when one goes to low (solvent and polymer) density that an attractive depletion regime can be identified.