Abstract

Conductivities of sodium dodecyl sulfate have been determined in water and in the presence of urea and acetamide at 298.15, 303.15, 308.15, 313.15 and 318.15 K. From the specific conductivity data, the critical micellar concentration, degree of counter ion association, degree of counter ion dissociation and standard free energy of micellization, standard enthalpy of micellization and standard entropy of micellization of sodium dodecyl sulfate have been computed. The thermodynamic parameters of micellization and effect of additives on these parameters have been used to study the interactions present in the micellar systems. Surfactants are found to enhance the diffusion significantly depending on hydrophobic/hydrophilic group lengths and the structure of the surfactant molecule. Aggregation properties of sodium dodecyl sulfate (SDS) in the presence of additives like urea and acetamide at various temperatures have been measured by the conductometric study in aqueous solution. The experimental data of aqueous-urea and acetamide solutions as a function of SDS concentration ranging from 1 to 14 mM dm ⁻³ show the presence of inflexion points indicating micellization and interaction mechanisms. CMC of surfactant increases with increase in temperature in a narrows range of composition. Considering CMC as a function of temperature, various thermodynamic parameters have been evaluated viz: (a) the standard enthalpy change (ΔH⁰_m), (b) standard entropy change (ΔS⁰_m) and (c) standard Gibbs energy change (ΔG⁰_m), The variation in these parameters with the concentration of surfactant and with the change in temperature suggests the manifestation of hydrophobic interactions in the studied system.

Keywords

Micellization, Electrical conductivity, Sodium dodecyl sulfate, Urea, Acetamide