Abstract:

Sub-zero temp. differential scanning calorimetry (SZT-DSC) was applied to a model nonionic water-in-oil microemulsion system based on: sucrose ester nonionic surfactants/water/1-butanol/n-alkanes (C12-C16). The max. water solubilization was 40, 56 and 80% for the systems contg. n-dodecane, n-tetradecane and n-hexadecane as the oil phase, resp. Two types of solubilized water were detected, the so-called bulk (free) water present in the core of the microemulsion and the interfacial (bound) water attached at the interface to the surfactant (and/or butanol). The internal distribution of water within the microemulsions was detd. along two diln. lines (with 32 and 43% of the initial surfactant). For the n-dodecane system the max. interfacial(bound) water is 12 and 14% along the two diln. lines, resp.; above this water content a core of bulk (free) water is formed. The type of the oil and the butanol interfacial participation strongly affect the water internal distribution. Both the temp. of fusion, Tf, of the bulk (free) water and of the interfacial (bound) water are strongly affected by butanol and oil. The nature of the surfactant, its fatty chain length and its HLB also affect the binding capability and capacity of water in microemulsion systems. For both n-dodecane and n-hexadecane, 11-13 mols. of water can be bound to the surfactant at the interface. [on SciFinder(R)]