CALORIMETRIC STUDY ON THE SOLUBILIZATION OF BUTANOL BY ALKYLPHOSPHATEAND ALKYLPHOSPHATE-LECITHIN SYSTEMS

Microcalorimetric studies on alkylphosphate-butanol and alkylphosphate -butanol-lecithin systems were carried out as a first step to study th e role of butanol (used as cosurfactant) in the formation of microemul sions. The enthalpy of solubilization; Delta H, of the same amount of butanol (1.806 mol kg(-1)) in aqueous sodium monoalkyl-phosphates, wit h a hydrocarbon chain varying from 6 to 10 carbon atoms, was investiga ted as a function of alkylphosphate concentration. Measurements were p erformed in the presence and in the absence of lecithin. The enthalpy values measured upon addition of butanol to the mixtures were negative in all cases. Below the critical micelle concentration (CMC) of the a lkylphosphates, the heats of butanol dissolution were found to decreas e upon increasing the concentration of the alkylphosphate. This behavi our was related to the dissolution of butanol in water and to the form ation of mixed butanol-alkylphosphate and butanol-alkylphosphate-lecit hin micelles. Above the CMC essentially constant Delta H values were f ound. The Delta H measured may be the sum of simultaneous effects-heat of alcohol dissolution and the simple alkylphosphate micelle dissocia tion or alkylphosphate-lecithin mixed aggregate dissociation and the h eat of mixed micelle formation. The Delta H at the plateaus were linea rly related to the corresponding CMC values of the alkylphosphates.