DSC spectra as thermal fingerprints of percolative microemulsions

Abstract

Three component percolative W/O microemulsions were studied by differential scanning calorimetry. Water-AOT-Decane, D2O-AOT-Decane, Water-AOT-Isooctane and Water-Ca(AOT)2-Decane systems were analyzed. Thus by changing, in the order, the dispersed phase, the dispersing medium, and by modifying the interphase region. The thermal history of the samples was monitored by a suitable thermal program. Following the latter, first order phase transitions associated with the freezing and/or melting of the two massive phases were obtained, as well as the higher order phase transition associated with the percolation process. From the melting spectra an estimate of the amount of water bound to the hydrophilic groups of the AOT as well as of that of oil bound to the hydrophobic surfactant tails was obtained. The latter result shows a difference in the behaviour of the continuous oily phase at the O/W interphase. From the freezing spectra, the percolative character of the microemulsion was evidenced by the exotherms associated with the freezing of the water phase.