Thermodynamics of the micellization process of carboxylates: A conductivity study

• Electrical conductivity was measured for five carboxylates in a broad temperature range.
• CMC and β parameter were estimated.
• By using pseudo-phase separation model and Gibbs–Helmholtz equation thermodynamic parameters of micellization were obtained.
• Δmiccpo were determined from the temperature dependence of ΔmicHo.
• Relation between Δmiccpo and the removal of water from the contact with surfactant molecules is discussed.

The micellization behaviour of the long-chain carboxylates: sodium octanoate (NaC8), sodium decanoate (NaC10), potassium decanoate (KC10), caesium decanoate (CsC10) and sodium dodecanoate (NaC12) in aqueous solutions were studied using electrical conductivity measurements between the temperatures (278.15 and 328.15) K. By using the pseudo-phase separation model and Gibbs–Helmholtz equation, the thermodynamic parameters for the micellization process were obtained from the temperature dependence of the critical micelle concentration, CMC, and the degree of micelle ionisation, β  . The heat capacity of micellization, Δmiccpo, estimated from the temperature dependence of enthalpy of micellization, ΔmicHo, were correlated with the size of the non-polar accessible surface area of the solvent, which is removed from contact with water during micellization. In all systems investigated, results suggest that the micelle core is still in contact with water molecules.

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