A DSC study of water behavior in water-in-oil microemulsions stabilized bysucrose esters and butanol

Sub-zero temperature differential scanning calorimetry (SZT-DSC) has been a pplied to a model nonionic water-in-oil microemulsion system based on: sucr ose esters/water/1-butanol/n-alkanes (C-12-C-16). The maximum water solubil ization was 40, 56 and 80 wt.% for the systems containing n-dodecane, n-tet radecane and n-hexadecane as the oil phase, respectively. Two types of solu bilized water have been detected. The so-called 'bulk' (free) water present in the core of the microemulsion and the 'interfacial' (bound) water attac hed at the interface to the surfactant (and/or butanol). The internal distr ibution of the water within the microemulsions was determined along two dil ution lines (with 32 and 43 wt.% of the initial surfactant). It was found t hat for the n-dodecane system the maximum 'interfacial'(bound) water is 12 and 14 wt.% along the two dilution lines, respectively. Above this water co ntent a core of 'bulk' (free) water is formed. The type of the oil and the butanol interfacial participation strongly affect the water internal distri bution. Both the temperature of fusion, T-f of the 'bulk' (free) water and of the 'interfacial' (bound) water are strongly affected by the butanol and the oil. The nature of the surfactant, its fatty chain length and its HLB also affect the binding capabilities and capacity of water in microemulsion systems. For both n-dodecane and n-hexadecane, 11-13 molecules of water ca n be bound to the surfactant at the interface. (C) 2000 Elsevier Science B. V. All rights reserved.