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Microcalorimetric Investigation of AOT Self-Association in Oil and the State of Pool Water in Water/Oil Microemulsions

1999; American Chemical Society; Volume: 103; Issue: 29 Linguagem: Inglês

10.1021/jp9838590

1520-6106

Pinaki R. Majhi, Satya P. Moulik,

Chemical and Physical Properties in Aqueous Solutions

The reverse micelle formation of AOT in n-heptane, n-octane, isooctane, n-decane, and eucalyptol has been microcalorimetrically studied. From the thermograms, the critical micellar concentration (cmc) and the energetic parameters of standard enthalpy and free energy and entropy of micellization (ΔHm, ΔGm, and ΔSm respectively) have been estimated. From the microcalorimetric titration of AOT/oil mixtures with water up to the phase separation point, the enthalpy of water dispersion (ΔHd) in the amphiphile/oil medium forming a microemulsion has been also determined. The water dissolution process has shown endothermic enthalpy changes in three distinct stages with an initial enthalpy maximum (except for the AOT/eucalyptol system). ΔHd has been estimated from the solubility limit, and the entropy of dispersion (ΔSd) has been consequently obtained from the Gibbs equation. The concentration of the dispersed microdroplets required in the above calculations has been estimated by measuring the droplet size by the DLS method and the known composition of the solution.