ON THE NATURE OF STATIC INTERACTIONS BETWEEN SURFACES SEPARATED BY A POLYMER-SOLUTION

Experiments with a surface force apparatus have been performed on stat ic interactions between solid surfaces separated by solutions of high molecular weight polybutadiene. Static forces have been defined at the end of the dynamic component relaxation created by the sphere displac ement. Measurements of interaction forces have been performed both as a function of solution concentration and surface separation. Concentra tion has been varied from the dilute to the semi-dilute regime. Two di stinct types of behaviour were observed when the concentration was var ied. Below C, the threshold of the semi-dilute regime, the structure of the adsorbed layers was found to be mainly responsible for the forc e variations. Above C, a depletion of free chains at the surface of t he adsorbed layers will contribute to the measured attraction. These e xperiments are closely related to stabilisation and destabilisation by depletion, phenomena which are observed in suspensions.