Fluorescence Probe Studies of the Aggregation State of Surfactants in Aqueous Polymer Solutions

Abstract

The interaction between polymers (polyethyleneoxide, POE, and polyvinylpyrrolidone, PVP) and ionic surfactants (sodium dodecylsulfate, SDS, and tetradecyltrimethylammonium bromide, TTAB) has been studied in aqueous solution bv means of conductivity and fluorescence probing (fluorescence decay of micelle-solubilized pyrene, fluorescence spectra of micelle-solubilized pyrene and dipyrenylpropane). The difference of behavior noted, with both POE and PVP, between SDS (strong interactions) and TTAB (very weak, if any interactions), clearly indicate that the polymer-surfactant interaction occurs at the micelle surface and strongly depends on the nature of the surfactant head group. The local concentration of the polymer repeat unit in the polymer coil, rather than the stoichiometric polymer concentration, determines the changes of critical micellization concentration (CMC) and micelle ionization degree. The fluorescence probing methods show that the SDS micelles bound to POE are smaller than the micelles formed in the absence of POE: the larger the polymer concentration or the smaller the surfactant concentration, the smaller the micelle size. The fluorescence emission spectrum of the micelle solubilitized pyrene also indicate a more open water-penetrated structure of the POE-bound SDS micelles. The results for the PVP-SDS system are somewhat similar to those for the POE-SDS. However some results suggest a possible specific interaction between the fluorescence probe and PVP, which makes difficult the study of the interaction between this polymer and surfactants.