ADSORPTION OF POLYMERS AT THE SURFACE CONCENTRATIONS IN THE DILUTED TO SEMIDILUTED REGIMES

The polymer adsorption regimes that correspond to very diluted bulk co ncentration and diluted to semidiluted surface concentration (on the s olid substrate) were studied both theoretically and experimentally. Th e extremal behavior of the adsorbed polymer layer was observed experim entally with two independent methods: (1) contact angle measurements o f adsorbed polymer films of poly(nonyl acrylate) and poly(methyl metha crylate) (PMMA) on the surface of aluminum foil and (2) electrochemica l reduction of K3Fe(CN)(6) on the surface of a platinum electrode cove red by the adsorbed polymer layer. As recently reported (Adsorp. Sci. Technol. 1996, 14, 251), the same behavior was observed on the surface of ZnO powder. The extremal behavior was found at polymer concentrati ons of about 0.001% in the bulk, or 1-5% from the plateau adsorption v alue. We suggest these data can be explained by the sharp change of co nformation (and fraction of bonded units per chain) of adsorbed macrom olecules when the transition from the diluted to semidiluted regime oc curred. The calculations performed on the basis of the partition funct ion combined with an associative integral equation predict the extremu m in the surface coverage due to specific dependence of the intramolec ular correlation function on the volume concentration of polymer.