Interaction between irreversibly adsorbed polymer layers: Is the mean field picture really inadequate?

We found out that the mean-field theory (MFT), if done consistently, is in good agreement with experimental observations for the force between irreversibly adsorbed polymer layers. This result is fairly unexpected in light of the conventional Cahn-de Gennes mean-field (CdGMF) theory that claims this force is zero. We reexamine the CdGMF equations and show that the consistency of the CdGMF approach is broken. This motivated us to derive an equation for the polymer density on the adsorbing surface that describes a minimum of the surface free energy. This equation replaces the conventional boundary condition used in CdGMF. The disjoining pressure is calculated by making use of the developed theory. An excellent agreement with the experimental results is indicated. We believe that our findings rehabilitate the mean-field theory as one of the most powerful tools for investigating the polymer-mediated interaction between colloids. Our result show that the unphysical predictions of CdGMF are due to its inconsistency rather than because this approach is "completely inadequate to discuss the plate-plate interactions in good solvent" [Macromolecules 15, 492 (1982)]].