A Partition Equilibrium Study of Benzene/Water/Sds-Butanol Oil/Water Microemulsions

Abstract

Partition of a sulfonephthalein dye, viz., phenol red, between the pseudophases in oil/water benzene/water/SDS-butanol microemulsions has been studied by UV-VIS spectroscopy and the partition equilibrium constants have been correlated with the microstructure of microemulsions and effect of cosurfactant.

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 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 (…”

“…The method has been applied to predict apparent pK a of the dyes in micellar solutions of surfactants of different charge types, where the dye is partially incorporated into the micelles (14)(15)(16). 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 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.…”

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

“…So, we can assume that the dye is partitioned only between the interface and the bulk water. As the D 2form of the dye is unlikely to be incorporated to the negatively charged interface, we can express the equilibrium of the dye in the o/w microemulsions as: 2 The partition constant K s were determined by using Eqn (2) described earlier: 2,5b It is interesting to note that the association constant increased quite linearly with increase in the oil fraction for all pH values. The values of R 2 for the linear fittings of K s vs volume fraction of benzene were 0.9901, 0.9968, 0.9913 and 0.9157 for pH 7.04, 7.43, 7.75 and 8.32 respectively.…”