THICKNESS OF ADSORBED POLYMER LAYERS AT A LIQUID-SOLID INTERFACE AS A FUNCTION OF BULK CONCENTRATION.

With a glass apparatus which is capable of measuring the thickness of adsorbed polymer layers with an accuracy of 0. 5 nm, determinations on adsorbed polystyrene layers in contact with extremely dilute solutions (ca. 10** minus **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 decreasing 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** minus **5 g/ml, which is the plateau usually described.