C. Ramachandran, S. Vijayan, D. Shah
Jun 12, 1980
Citations
0
Influential Citations
13
Citations
Journal
The Journal of Physical Chemistry
Abstract
The middle phases obtained by varying the sodium chloride concentration in surfactant formulations containing 5:3 (wt/wt) TRS 10-410 (a petroleum sulfonate)-isobutyl alcohol and equal volumes of aqueous and oil phases were studied by using spin-labeling techniques. Two different spin-labels, one partially water soluble (5-doxylstearic acid label) and the other water insoluble (3-doxylcholestane label), were used. Extensive measurements of electrical conductivity and phase volumes of the middle phases were also carried out. These physical property results corroborated the spin-label studies in that below 2.0 wt % NaCl the middle phase was essentially a microemulsion of the water external type. Beyond 2.3% NaCl the appearance of a signal component typical of a free label (ketostearic acid) in an oil environment and changes in correlation time characteristics (cholestane label) coupled with physical property data underlined a qualitative change in the microemulsion system. It is believed that these changes are consistent with a transition from a water-external type to an oil-external type microemulsion system. This transition is estimated to be around 2 to 2.3% NaCl. The results are further substantiated by ascorbic acid reduction rate studies. Possible mechanisms of this transition are discussed.