Partition of bromophenol blue in toluene/water/sodium bis(2‐ethylhexyl)‐sulfosuccinate water‐in‐oil microemulsions

The partition of bromophenol blue between oil‐water interfaces and water droplets in water‐in‐oil microemulsions of toluene/water/sodium bis(2‐ethylhexyl)sulfosuccinate was studied by a spectroscopic method at different water fractions and pH. The partition equilibrium constant, Kp, between the two domains decreased considerably with an increase in the water fraction and pH. The decrease in Kp with an increase in the water fraction suggests the retention of more dye molecules in water. The decrease in Kp with an increase in pH has been attributed to a lower tendency of the base form to associate with the anionic oil‐water interface compared with that of the acid form and to an increase in the negative charge density at the oil‐water interface at a higher pH.