Approximate prediction of adhesion between two solids immersed in surfactant solution based on adsorption to an isolated solid

A thermodynamic argument is used to predict the adhesion between two solid surfaces in surfactant solutions from the adsorption to a single (isolated) solid. The model is based on the concept that the difference in energy of the two solids in contact and separated states can be predicted from the difference in adsorption in the contact and separated states. To make quantitative predictions, we assume that the adsorption of surfactant in ‘contact’, Γs0Γs0, is approximately equal to the adsorbed surfactant on an isolated surface when the net charge is zero (at the charge compensation point). Changes in the adhesion are determined from the changes in adsorption required to reach Γs0Γs0 from the adsorption at infinite separation, Γ∞. Experimental measurements of the adhesion using colloidal probe atomic force microscopy (AFM) are in reasonable agreement with our method.