COMPETITIVE ADSORPTION BETWEEN NONIONIC POLYMERS AND SURFACTANTS ON SILICA

The competitive adsorption on silica between non-ionic surfactants of the alkylphenol poly(ethylene oxide) type and neutral polymers of the poly(ethylene oxide) type has been investigated as a function of polym er chain length by determining adsorption isotherms of 50:50 wt.% mixt ures. For molecular weights of the polymer below 10 000 g mol(-1), sur factant adsorption at saturation is not affected by the presence of th e polymer. For higher molecular weights, polymer molecules are prefere ntially adsorbed at low concentrations, whereas at higher concentratio ns the behaviour of these systems can be characterized by a threshold molecular-weight value, above which the polymer displaces the surfacta nt. The results are interpreted by the competition between two types o f macromolecules: the adsorbed polymer and the surfactant surface aggr egate. (C) 1997 Elsevier Science B.V.