Calorimetric studies of microemulsion systems with lecithin, isooctane and butanol

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In the present study, a thermodynamic analysis was performed using an isothermal titration microcalorimeter to measure changes in the enthalpy of mixing (ΔmixH) of water in microemulsion systems formed by soybean lecithin, isooctane and butanol. These energies were important to determine the driving forces associated with the formation of reverse micelles. It was observed that the titration curves of water in pure isooctane and in isooctane with soybean lecithin present values of ΔmixH equal to −9.46×10−3kJ/mol and −5.68×10−3kJ/mol, respectively. This shows that water does not form intermolecular interactions with these components. Exothermic behavior, with values of ΔmixH ranging from +2.17kJ/mol to −1.63×10−2kJ/mol, was observed from the titration curve of water in systems formed by soybean lecithin, isooctane and butanol. These values were associated with the water dissolution process, where the formation of reverse micelles had been observed in the evaluated systems. Differences in behavior of ΔmixH for the water curves were observed in systems formed by butanol and soybean lecithin, only pure butanol and butanol with isooctane. The curve of the system containing soybean lecithin, butanol and isooctane clearly shows that the formation of aggregates occurred in this system (reverse micelles). Finally, it was also noted that soybean lecithin did not suffer any degradation process, since the energy involved in the process of water titration in the systems containing the same substance was considered low. Thus, soybean lecithin may be used without problems in this type of system.