Inhomogeneous model colloidpolymer mixtures: Adsorption at a hard wall
Abstract
We study the equilibrium properties of inhomogeneous model colloidpolymer mixtures. By integrating out the degrees of freedom of the ideal polymer coils, we derive a formal expression for the effective onecomponent Hamiltonian of the (hard sphere) colloids that is valid for arbitrary external potentials acting on both the colloids and the polymers. We show how one can recover information about the distribution of polymer in the mixture given knowledge of the colloid correlation functions calculated using the effective onecomponent Hamiltonian. This result is then used to furnish the connection between the freevolume and perturbation theory approaches to determining the bulk phase equilibria. For the special case of a planar hard wall the effective Hamiltonian takes an explicit form, consisting of zero, one, and twobody, but no higherbody, contributions provided the size ratio q=σ_{p}/σ_{c}<0.1547, where σ_{c} and σ_{p} denote the diameters of colloid and polymer respectively. We employ a simple density functional theory to calculate colloid density profiles from this effective Hamiltonian for q=0.1. The resulting profiles are found to agree well with those from Monte Carlo simulations for the same Hamiltonian. Adding very small amounts of polymer gives rise to strong depletion effects at the hard wall which lead to pronounced enhancement of the colloid density profile (close to the wall) over what is found for hard spheres at a hard wall.
 Publication:

Physical Review E
 Pub Date:
 April 2001
 DOI:
 10.1103/PhysRevE.63.041405
 Bibcode:
 2001PhRvE..63d1405B
 Keywords:

 82.70.Dd;
 61.20.Gy;
 68.43.Mn;
 Colloids;
 Theory and models of liquid structure;
 Adsorption/desorption kinetics