Micellar parameters of diblock copolymers and their interactions with ionic surfactants

Abstract

The interactions of non-ionic amphiphilic diblock copolymer poly(oxyethylene/oxybutylene) (E39B18) with anionic surfactant sodium dodecyl sulphate (SDS) and cationic surfactant hexadecyltrimethylammonium bromide (CTAB) were studied by using various techniques such as surface tension, conductivity, steady-state fluorescence and dynamic light scattering. Surface tension measurements were used to determine the critical micelle concentration (CMC) and thereby the free energy of micellization (ΔGmic), free energy of adsorption (ΔGads), surface excess concentration (Γ) and minimum area per molecule (A). Conductivity measurements were used to determine the critical micelle concentration (CMC), critical aggregation concentration (CAC), polymer saturation point (PSP), degree of ionization (α) and counter ion binding (β). Dynamic light scattering experiments were performed to check the changes in physiochemical properties of the block copolymer micelles taken place due to the interactions of diblock copolymers with ionic surfactants. The ratio of the first and third vibronic peaks (I1/I3) indicated the polarity of the pyrene micro environment and was used for the detection of micelle as well as polymer-surfactant interactions. Aggregation number (N), number of binding sites (n) and free energy of binding (ΔGb) for pure surfactants as well as for polymer-surfactant mixed micellar systems were determined by the fluorescence quenching method.