Catastrophic phase inversion of abnormal emulsions in the vicinity of the locus of transitional inversion

摘要

This paper deals with the phase behaviour of model abnormal emulsions of cyclohexane/water/polyethoxylated surfactant in the vicinity of the locus of transitional inversion (optimum formulation). Abnormal emulsions are formed under dynamic conditions if the phase containing the soluble surfactant becomes the dispersed phase. Phase maps have been suggested in the literature that define the boundaries of emulsion morphologies. On these maps, only one transformation can be observed for any formulation scan. Furthermore, the morphology of emulsions in the vicinity of the locus of transitional inversion is rather vague. One might assume that by changing the HLB of the surfactant used in an abnormal emulsion to favour the continuous phase, that abnormal emulsion will gradually transform to a normal emulsion of the same type. A new experimental procedure was adopted in which emulsification was started with abnormal emulsions. To transform the abnormal emulsions to the normal emulsion of the same type, they were exposed to variations in temperature, the surfactant HLB, or water-oil phase ratio. As the optimum formulation was approached, the abnormal emulsions became so unstable that could not exist anymore in the un-favoured morphology and inverted to the normal emulsion of the opposite type. Further variation in the formulation along the route led to a transitional inversion to the normal emulsion of the original type. The result indicates an important finding that the transformation of abnormal emulsions to normal ones of the same type occurred via two successive inversions of catastrophic and transitional nature. It appears that the boundaries of catastrophic inversion correspond to the emulsions with the finest drop size. A modification to the phase behaviour maps, to include the locus of catastrophic phase inversion in the vicinity of the transitional inversion, was thus suggested. (C) 2004 Elsevier B.V. All rights reserved.