Surface tension of mixed non-ionic surfactant/protein solutions: comparison of a simple theoretical model with experiments

A thermodynamic model is derived for the description of the equilibrium adsorption at the surface of a solution containing a protein and a non-ionic surfactant. The derived model allows to determine the dimensionless surface pressure of a mixed solution on the basis of the dimensionless surface pressure of the individual solutions of the protein and surfactant, respectively. Experimental data for human serum albumin mixed with decyl dimethyl phosphine oxide and β-lactoglobulin mixed with Tween 20 agree well with the calculated values.