Temperature-induced intermicellization and contraction in aqueous mixtures of sodium dodecyl sulfate and an amphiphilic diblock copolymer.
Aqueous solutions of a thermoresponsive amphiphilic diblock copolymer, containing poly(N-isopropylacrylamide), in the presence of the anionic sodium dodecyl sulfate (SDS) surfactant can undergo a temperature-induced transition from loose intermicellar clusters to collapsed core-shell nanostructures. The polymer-surfactant mixtures have been characterized with the aid of turbidity, small-angle neutron scattering (SANS), intensity light scattering (ILS), dynamic light scattering (DLS), shear viscosity, and rheo-small angle light scattering (rheo-SALS). In the absence of SDS, compressed intermicellar structures are formed at intermediate temperatures, and at higher temperatures further aggregation is detected. The SANS results disclose a structure peak in the scattered intensity profile at the highest measured temperature. This peak is ascribed to the formation of ordered structures (crystallites). In the presence of a low amount of SDS, a strong collapse of the intermicellar clusters is observed at moderate temperatures, and only a slight renewed interpolymer association is found at higher temperatures because of repulsive electrostatic interactions. Finally, at moderate surfactant concentrations, temperature-induced loose intermicellar clusters are detected but no shrinking was registered in the considered temperature range. At a high level of SDS addition, large polymer-surfactant complexes appear at low temperatures, and these species are compressed at elevated temperatures. The rheo-SALS results show that the transition structures are rather fragile under the influence of shear flow.
Pamies
Ramón
R
Department of Chemistry, University of Oslo, P.O. Box 1033, N-0315 Oslo, Norway.
Zhu
Kaizheng
K
Kjøniksen
Anna-Lena
AL
Knudsen
Kenneth D
KD
Nyström
Bo
B
D000178:Acrylamides / Q000737:chemistry*; D008027:Light; D008823:Micelles; D009391:Nephelometry and Turbidimetry; D033363:Neutron Diffraction; D011092:Polyethylene Glycols / Q000737:chemistry*; D012212:Rheology; D012542:Scattering, Radiation; D053838:Scattering, Small Angle; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature; D014783:Viscosity
D000178:Acrylamides; D008823:Micelles; D013501:Surface-Active Agents; C524382:methoxy-poly(ethylene glycol)-block-poly(N-isopropylacrylamide); D012967:Sodium Dodecyl Sulfate; D011092:Polyethylene Glycols