Thermodynamics of Formation of Biological Microemulsion (with Cinnamic Alcohol, Aerosol OT, Tween 20, and Water) and Kinetics of Alkaline Fading of Crystal Violet in Them

The ternary phase diagrams for the formation of biological microemulsions of the combinations CA/AOT/water and CA/Tween 20/water have been presented. The thermodynamics of solution of water in AOT/CA as well as in Tween 20/CA forming w/o microemulsions and solution of oil in Tween 20/water forming o/w microemulsions have been calorimetrically studied. The solution processes are essentially exothermic (with a few exceptions) and have yielded negative entropies, i.e., producing an ordering effect. This has been supported by the measured specific heats of the resulting solution. The pseudo-first-order rate constants (k1) for the alkaline fading of crystal violet in w/o microemulsion medium for the CA/AOT/water and CA/TW 20/water have been found to depend on [water]/[AOT] mole ratio (omega) with maxima at omega = 10. For o/w preparations of CA/TW-20/water, k1 has shown maximum at [CA]/[TW-20] mole ratio omega' = 2, whereas the k2 value has increased with omega'. The salt effect on the reaction has shown significant deviation from expectation in w/o microemulsion. The free energies of activation for the w/o and o/w systems are of the same order, whereas both DeltaHdouble dagger and DeltaSdouble dagger values differ significantly.