Density functional study of surface forces in solutions containing star-shaped polymers

Density functional theory is used to study polymer solutions between surfaces in equilibrium with a bulk solution. We investigate the effect on the surface interaction free energy of having star polymers with different numbers of arms. In addition, we consider the role played by the strength of the adsorption potential and the concentration of the polymer molecules. The interaction free energy is found to scale quite well with the number of arms on the stars, and the separation dependence of the interaction scales approximately with the radius of gyration. When the adsorption potential is weak, the polymer molecules are depleted. A free energy barrier is nevertheless present-a phenomenon often referred to as depletion stabilization. The barrier scales with the number of arms on the star polymers.