Tunable Surface Interactions In Adsorbing Polymer Solutions

A simple formalism is suggested, to calculate the most likely configuration of a finite polymer, between two surfaces on which the monomers can adsorb. Grafted polymers typically enhance the stability of colloidal dispersions, via the long ranged steric repulsion due to the overlap of their polymer brushes, which can be thicker that the typical range of the DLVO interactions. However, if the polymers are adsorbing on the colloidal surfaces, there is the possibility of bridge formation between particles and therefore long-range attractions are induced (a procedure commonly used for the flocculation of colloidal suspensions). The two effects are competing and might result in attractive interactions at larger distances and repulsive interactions at shorter distances. These distances, as well as the magnitude of the interactions, depending on the system parameters, such as the grafted density in the brush, the length of the polymer, the adsorption energy between monomers and surfaces, the quality of the solvent or the polymer charge (for polyelectrolytes). It is also shown that at large adsorption energies for monomers on surfaces, the polymers are mostly collapsed on one surface and very few bridges between surfaces are created, therefore the bridging interaction is weak. On the other hand, at very low adsorption energies, although there are more bridges formed, the long-range interactions between surfaces are also weak. Our procedure allows one to calculate the parameters for which attractions or repulsions can be obtained at any desired distance and therefore to tailor the system interactions for the application required