Microemulsions and emulsions in DDAB/W/oil systems

Some DDAB/W/oil phase diagrams have been investigated with the highlight on the microemulsion and emulsion regions. In previous studies it has been demonstrated that DDAB easily forms w/o microemulsions with linear aliphatic and cycloaliphatic oils. In this work the aromatic oils toluene and trifluoromethylbenzene, semifluorinated linear alkane oils of the type CnH2n+1CmF2m+1 and a perfluoropolyether oil have been considered. DDAB is soluble up to similar to 30 wt.% in the aromatic oils, whereas it is insoluble in the others. The phase diagrams of DDAB/W/aromatic oil systems show a microemulsion region near the oil-DDAB axis, and up to a water content of similar to 15 wt.%. NMR relaxation times and conductivity measurements allowed to characterize the microemulsion structure. The other systems present emulsion areas, which are obtained by a gradual addition of small amounts of water (4-5 wt.%) followed by vigorous mixing. These emulsions have been shown to be stable over more than two years. Optical microscopy and preliminary NMR self-diffusion measurements are presented to give the hint of the microstructural features. (C) 1999 Elsevier Science B.V. All rights reserved.