Interaction of hydrophobically end-capped poly(ethylene oxide) with nonionic surfactants in aqueous solution. Fluorescence and light scattering studies

In ternary mixtures of an associative polymer (AP), hydrophobically end-capped poly(ethylene oxide), C(12)EO(460)C(12), and the nonionic surfactant, C(12)E(8), hydrophobic microdomains are formed at much lower concentrations than the cac and cmc of the binary systems. Strong interactions promote formation of large networks and result in a substantial depression of the cloud point temperature, CPT (below that of the polymer and the surfactant), a decrease in the diffusion coefficient, and an increase in the solution viscosity. A more hydrophobic surfactant is more effective in forming these structures. At higher relative surfactant concentrations, however, the networks dissolve and the CPT increases. A second more hydrophobic AP added to a C(12)EO(460)C(12) solution does not change the solution structure in the same way. In mixtures of two APs, the CPT is found to lie in between those of the two polymers. The networks formed in this case are always smaller than those formed by either of the APs. Addition of an AP to a C(12)E(8) solution slightly increases the total aggregation number of the hydrophobic domains above that of the pure surfactant aggregates. At concentrations where the surfactant structure dominates, the added polymer has been found to associate with the existing domains rather than forming new ones. The bulky hydrophobic groups of the AP in the ternary mixture effectively prevent the increase in N-agg with temperature observed in pure C(12)E(8) systems and also in the presence of unmodified PEG.