The thickness of adsorbed polymer layers at a liquid–solid interface as a function of bulk concentration

Abstract

With a glass apparatus which is capable of measuring the thickness of adsorbed polymer layers with as accuracy of 0.5 nm, determinations on adsorbed polystyrene layers in contact with extremely dilute solutions (ca. 10⁻⁷ g/ml) in toluene were performed. Thermodynamic equilibrium was proved to exist between the adsorbed polymer layer and bulk solution. The thicknesses found suggest that a fluid mechanical effect is operative, as has recently been calculated. It was shown that in the very dilute region the thickness of the adsorbed layer is initially a linearly increasing function of concentration, and that regions of (very low) concentrations exist over which a first plateau arises, where the layer is as thin as might be expected from isolated, adsorbed coil analysis. A second much higher plateau arises at concentrations in excess of 10⁻⁵ g/ml, which is the plateau usually described.