Intermolecular Interactions of Polymer/Surfactants Mixture in Aqueous Solution Investigated by Various Techniques

The interaction between diblock copolymer with ionic surfactants in aqueous solution were studied employing surface tensiometery, electrical conductivity, steady-state fluorescence spectroscopy and dynamic laser light scattering at 303K. Surface tension measurements were used to determine critical micelle concentration (CMC) and, thereby, its free energy of micellization (G(m)), free energy of adsorption (G(ads)), surface excess concentration (), and minimum area per molecule (A). The negative values of (G(m)) both in case of SDS and CTAB confirmed the spontaneity of the processes. Conductivity measurements were used to determine critical micelle concentration (CMC), critical aggregation concentration (CAC), polymer saturation point (PSP), degree of ionization (), and counterion binding (). Addition of polymers could effectively reduce the CMC value of surfactants and, thus increase the detergency. Dynamic light scattering experiments were performed to check the changes in physiochemical properties of the block copolymer micelles take place due to the interactions of diblock copolymer with ionic surfactants. The ratio of (I-1/I-3) indicates the polarity of the pyrene micro environment and confirms the detection of micelle as well as polymer-surfactant interactions. Aggregation number (N), number of binding sites (n), and free energy of binding (G(b)) for pure surfactants as well as for polymer-surfactant mixed micellar systems were determined by fluorescence quenching method.