Polymer depletion interaction between a colloid particle and a wall: A Monte Carlo study

Abstract

An off-lattice bead–spring model of a polymer solution in a container with impenetrable walls is used to study the depletion interaction of a colloid particle with the planar wall by means of a Monte Carlo simulation. As expected, this interaction is found to depend essentially on the ratio ρ=R/Rg of the particle radius R to the mean radius of gyration Rg of the polymer chains in the case of dilute and semidilute solutions. For large particle to polymer size ratio ρ>1 this effective force is attractive and decreases steadily with growing distance D of the colloid from the wall. It is found to scale linearly with ρ in agreement with recent theoretical predictions. In the opposite case of ρ<1 the depletion force is found to change nonmonotonically with D and go through a maximum at a particular distance Dmax⩽Rg. In both cases, however, local variations of the polymer density profile, which we detect at higher polymer concentrations, are found to influence the depletion force and even to change it locally from attraction to repulsion. The monomer density distribution far away from/or around the colloid in the vicinity of the wall is also investigated and related to the observed behavior of the depletion force.