Effect of buffers on partition equilibrium of phenol red in benzene/water/SDS-butanol oil/water microemulsions

Abstract

The effect of buffer on the partition of phenol red, an anionic dye, between the oil-water (o/w) interface, oil droplet core and the buffered bulk water in benzene/water/SDS-butanol o/w microemulsions have been studied with phosphate and Tris buffer systems.

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

“…Therefore, the dye could partition only between the aqueous pseudophase and the oil-water interface (17)(18)(19). The presence of the isosbestic point indicates the presence of an equilibrium between the dye in the aqueous pseudophase of the droplets and the oil-water interface, no matter in which form the dye existed in the aqueous pseudophase (14)(15)(16)(17)(18)(19). Similar variations were observed in the visible spectra of BPB in the w/o microemulsions of water in toluene with different volume fractions of water.…”

“…The partition constant decreased with an increase in the water fraction for all fixed pH values. This trend was just opposite that observed for K p with increasing oil fractions in the case of the partition of phenol red in o/w benzene/water/sodium dodecyl sulfate/cosurfactant microemulsions (18,19). The observation is, however, similar to the decrease in incorporation of alkanols into reverse micelles of water/AOT/n-heptane with an increase in the water/AOT ratio (23).…”

“…The partition coefficient, C p , of the dye between the interface and the bulk water of the droplets is defined as (19). K p can then be determined for various systems at fixed pH by using Equation 3, derived by a method described earlier (17)(18)(19): [3] where d o , d, and d i are the absorbances of the dye at the λ max of the decreasing band, i.e., 592 nm, in the absence, presence, and excess of AOT, respectively. The plots of (…”

“…Recently, this partition equilibrium approach has been extended to o/w (oil-in-water) microemulsions to gain information on microemulsion microstructure and behavior (17). We have also applied the partition equilibrium approach to study the effects of alcohols as cosurfactants and the change in pH on partition equilibrium of a dye, viz., phenol red in o/w microemulsions (18,19). The partition equilibrium approach is a simple and time-saving approach, and the studies add to the lack of direct information on microemulsion microstructure, with some assumptions widely present in the literature.…”

“…The partition equilibrium approach is a simple and time-saving approach, and the studies add to the lack of direct information on microemulsion microstructure, with some assumptions widely present in the literature. The studies carried out so far have involved only o/w microemulsions stabilized by anionic surfactants, viz., sodium dodecyl sulfate and sodium dodecyl benzene sulfonate (17)(18)(19), both requiring a cosurfactant to meet the geometric requirement for forming microemulsions (20). Therefore, we thought it worthwhile to carry out a similar study with water-in-oil (w/o) microemulsions, without using a cosurfactant.…”