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    Critical Incorporation Concentration of Surfactants Added to Micellar Solutions of Hydrophobically Modified Polyelectrolytes of the Same Charge

    Year: 2001

    Journal: Langmuir 2001, 17, 2937-2941, 20111221

    Authors: Ralph H. Colby, Nopparat Plucktaveesak, and Lev Bromberg

    Organizations: Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, and Department of Physics and Center for Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

    Polymer-surfactant interactions in aqueous solutions of the surface-active copolymer poly(ethyleneoxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-g-poly(acrylic acid) and a homologous series of alkyl sulfates are studied. When surfactants of the same charge are added to copolymer solutions that already have micelles, the surfactant starts to incorporate into the existing polymer micelle at the critical incorporation concentration (CIC). Surface tension measurements determine the CIC as a local minimum in surface tension as a function of added surfactant. Fluorescence emission measurements using a selective fluorescent probe indicate that the surfactant incorporation is noncooperative. Because the initial incorporation at the CIC only involves a single surfactant entering a nonionic micelle, no counterion condensation is needed, making the tail-length dependence of the CIC similar to the tail-length dependence of the critical micelle concentration of nonionic surfactants.