EFFECT OF SODIUM COUNTERION SUBSTITUTION BY LITHIUM ON THE INTERACTION OF DODECYL-SULFATE WITH POLY(ETHYLENE OXIDE) IN AQUEOUS-SOLUTION

The interaction of sodium dodecylsulfate (SPS) and lithium dodecylsulf ate (LDS) with poly(ethylene oxide) in aqueous solution has been inves tigated by surface tension and fluorescence measurements, The critical concentrations for the onset of micellization of the surfactants on t he polymer and the amount of the surfactant taken up by the polymer at saturation were determined. Experiments have been performed in salt-f ree solutions as well as in the presence of 0.1 M of alkaline halides containing the same cation as the surfactant counterion. For all the e xperimental conditions employed it is found that, upon substitution of sodium by lithium both of the characteristic parameters for the adsor ption of the surfactant on the polymer are modified in a manner indica tive of a stronger interaction with SDS than with LDS. The results are interpreted in terms of a surfactant interaction affected by the affi nity of the counterion for complexation with the polymer.