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 en d-capped poly(ethylene oxide), C(12)EO(460)C(12), and the nonionic sur factant, C(12)E(8), hydrophobic microdomains are formed at much lower concentrations than the cac and cmc of the binary systems. Strong inte ractions promote formation of large networks and result in a substanti al depression of the cloud point temperature, CPT (below that of the p olymer and the surfactant), a decrease in the diffusion coefficient, a nd an increase in the solution viscosity. A more hydrophobic surfactan t is more effective in forming these structures. At higher relative su rfactant concentrations, however, the networks dissolve and the CPT in creases. A second more hydrophobic AP added to a C(12)EO(460)C(12) sol ution does not change the solution structure in the same way. In mixtu res of two APs, the CPT is found to lie in between those of the two po lymers. 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) solutio n slightly increases the total aggregation number of the hydrophobic d omains 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 o nes. The bulky hydrophobic groups of the AP in the ternary mixture eff ectively prevent the increase in N-agg with temperature observed in pu re C(12)E(8) systems and also in the presence of unmodified PEG.