CALORIMETRIC INVESTIGATION OF WATER LECITHIN/CYCLOHEXANE MICROEMULSIONS/

The enthalpies of dilution of water/lecithin/cyclohexane microemulsion -gels at various R values (R=[water]/[lecithin]) and molar enthalpies of solution of water in lecithin/cyclohexane at a fixed lecithin conce ntration were determined calorimetrically at 25 degrees C. Through a d escription of the process of dilution of water/lecithin/cyclohexane mi croemulsion-gels as one involving mainly the scission of lecithin reve rsed micelles in to smaller ones, the concentration dependence of the enthalpy was rationalized. Surprisingly, in order to account for the d ilution enthalpies, it was not necessary to hypothesize a thermal effe ct arising from the breakage of the micellar network present in the mi cremulsion-gels. This result indicates that the building-up of the mic ellar network mainly arises from topological entanglements and steric hindrances among the lecithin reversed micelles. Attribution of the mo lar enthalpy of solution of water essentially to the thermal effect ar ising from the intermicellar aggregation process induced by the water addition allowed a rough estimation of the scission energy (the energy necessary to break an Avogadro's number of micelles) and of the micel lar aggregation number.