Enthalpy-entropy compensation in micellization of sodium dodecyl sulphate in water/methanol, water/ethylene glycol and water/glycerol binary mixtures

1435-1536

Enthalpy-entropy compensation ; cosolvent effects ; critical micelle concentration ; reference temperature ; temperature effects

Springer Online Journal Archives 1860-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract The enthalpy-entropy compensation in micellization of sodium dodecyl sulphate (SDS) in binary mixtures of water/methanol (MeOH), water/ethylene glycol (EG) and water/glycerol (GL) over a temperature range of 10–60°C was examined. When the cosolvent concentration was low, the critical micelle concentration (CMC) depended only on the total amount of the hydroxyl group added. When the cosolvent concentration was high, the increase in CMC followed the sequence: MeOH〉EG〉GL. Enthalpy and entropy changes were evaluated from which the compensation temperature was determined. Both enthalpy and entropy changes decreased on the addition of the cosolvents, indicating a lowering of solution hydrophobicity. The compensation temperature was found as a constant over the cosolvent concentration range, as a result, was not a good index for characterizing the solute/solvent interactions. The two reference temperatures at which the enthalpy-entropy change respectively became zero were strongly influenced by the cosolvent addition, therefore could serve as a proper index for solution hydrophobicity.

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