6533b7d0fe1ef96bd125b5e3

RESEARCH PRODUCT

Binding between (Ethylene Oxide)13−(Propylene Oxide)30−(Ethylene Oxide)13 and Sodium Decanoate. Volume, Enthalpy, and Heat Capacity Studies

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Volume, enthalpy, and heat capacity of transfer (ΔYt) of (ethylene oxide)13−(propylene oxide)30−(ethylene oxide)13 (L64), at some concentrations, from water to the aqueous sodium decanoate (NaDec) solutions as functions of the surfactant concentration (mS) were determined at 298 K. The copolymer was studied in both the unassociated and associated forms. For a given L64 concentration (mC), the ΔYt vs mS profiles for the volume and the enthalpy are equal but different from that of the heat capacity because the latter contains also the relaxation terms. The experimental data were analyzed by assuming the distribution of L64 between the aqueous and the micellar phases and the shift of micellization equilibrium induced by the copolymer. A very good fit was obtained at mC = 35 mmol kg-1, which provided the L64−micelles binding constant (Kb), the volume of transfer of L64 from water to micelles (ΔVt,M) and the Setchenov constant. By using Kb, ΔVt,M, and the L64-free surfactant interaction parameter (obtained fro...