Adsorption from oligomer-monomer solutions on the surfaces modified with end-grafted chains

A density functional theory has been applied to study adsorption from oligomer-monomer solutions on solid surfaces modified with end-grafted polymers. Chains are modeled as freely jointed tangent spheres. All spherical species interact via Lennard-Jones (12-6) potential. The grafted chains are not attracted by the surface. Fluid molecules interact with the substrate via Lennard-Jones (9-3) potential. It is shown how a shape of the relative excess adsorption isotherms depends on such parameters as the oligomer length, the grafting density, oligomer-substrate interactions, oligomer-grafted chains interactions, and oligomer-monomer interactions in the bulk solution. As attractive interactions between free and grafted chains strengthen, the relative excess adsorption isotherm can change from negative, through S-shaped with an adsorption azeotropic point, to positive in the whole concentration region. A change of oligomer-monomer interactions causes the opposite effects. For low grafting densities of attractive bonds, the relative excess of oligomers increases, reaches a maximum, and decreases. The structure of surface layers is also analyzed.