A study of the properties of water-in-oil microemulsions in the subzero temperature range by differential scanning calorimetry

Abstract

The thermal properties of two w/o microemulsions and one micellar solution were systematically investigated by means of differential scanning calorimetry (DSC). H₂O/hexadecane/K-oleate/hexanol and H₂O/dodecane/K-oleate/hexanol microemulsions with the mass ratios K-Oleate/hexanol=0.6 and (K-oleate+Hexanol)/oil=0.4 and a H₂O/AOT/isooctane 3 % micellar solution were studied as a function of increasing water concentration. Both DSC endothermal and DSC exothermal analyses were performed in the temperature interval 123–303 K. The dependence of the thermal properties upon both the particular temperature rate (1-2-4-6-8 K/min), and thermal cycling with repeated freezing/thawing runs, was studied. The freezing behavior of the water dispersed phase was analyzed in detail. Preliminary results are also reported about low temperature storage effects.

The analysis of endothermic processes due to the melting of water has shown that this component may exist into two configurations, namely, free and interphasal distinguished by the melting temperatures of 273 K and 263 K respectively. The exothermic analysis has proved very effective in the identification of the structural evolution of the systems as a function of water addition. The freezing temperature of the overcooled water fraction was found to exhibit a stepwise trend upon water addition, each “step” corresponding to specific and well defined both DSC-ENDO and DSC-EXO characteristics.