6533b870fe1ef96bd12cf968

RESEARCH PRODUCT

Calorimetric investigation of water/lecithin/cyclohexane microemulsions

subject

description

The enthalpies of dilution of water/lecithin/cyclohexane microemulsion-gels at variousR values (R=[water]/[lecithin]) and molar enthalpies of solution of water in lecithin/cyclohexane at a fixed lecithin concentration were determined calorimetrically at 25°C. Through a description of the process of dilution of water/lecithin/cyclohexane microemulsion-gels as one involving mainly the scission of lecithin reversed micelles in to smaller ones, the concentration dependence of the enthalpy was rationalized. Surprisingly, in order to account for the dilution enthalpies, it was not necessary to hypothesize a thermal effect arising from the breakage of the micellar network present in the micremulsion-gels. This result indicates that the building-up of the micellar network mainly arises from topological entanglements and steric hindrances among the lecithin reversed micelles. Attribution of the molar enthalpy of solution of water essentially to the thermal effect arising 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 micellar aggregation number.