Experimental Studies of Polymer Concentration Profiles at Solid-Liquid and Liquid-Gas Interfaces by Optical and X-ray Evanescent Wave Techniques

Interfacial systems in which polymer chains play a dominant role are ubiquitous in nature. For instance, oil-water emulsions are stabilized by block copolymers adsorbed at the liquid-liquid interface and bearing two long sequences immersed in each of the two phases, respectively (1) . Many colloidal suspensions would not exist if homopolymers did not provide a strong steric repulsion against grain coalescence by adsorbing on the solid particles. The process was actually discovered by the Egyptians 4000 years ago when they added arabic gum to carbon black to produce stable ink (2a,b). In the reverse case, hemocompatible materials must have surfaces inert with respect to the proteins contained in the blood. A well-known example of nonadsorbing plastic materials is dacron, which is used in artificial arteries, where gradual clogging by cake build-up must be avoided (3). To cite one last example, from among many which are important, tertiary oil recovery is based on the fact that aqueous polymer solutions become effective oil-displacers when the polymer concentration is such that the viscosities of the two fluids are approximately matched. The