Partition of n‐Butanol Among Phases and Solubilization Ability of Winsor type III Microemulsions

Abstract

AbstractThe partition of n‐butanol in Winsor type III (W‐III) microemulsions was investigated in this work. Three kinds of anionic surfactants (sodium dodecyl sulfate (SDS), sodium dodecyl sulfonate (DSS), and sodium dodecyl benzene sulfonate (SDBS)) and two kinds of anionic/cationic surfactant mixtures (SDS/octadecyl trimethyl ammonium chloride (OTAC) mixtures and DSS/OTAC mixtures) were studied. Internal standard gas chromatography was employed in n‐butanol content analysis. The results showed that no water exists in the excess oil (EO) phase and no oil exists in the excess water (EW) phase. For the W‐III microemulsions obtained by salinity scanning, relatively constant n‐butanol content in the EO (11–12 v%) and EW (1–4 v%) was found under different salinities. Accurate measurement of n‐butanol content in each phase is important for those systems having low solubilization ability. For the W‐III microemulsions prepared using SDS/OTAC surfactant mixture, the percentage of n‐butanol distributed into the interfacial layer decreased while the fraction of n‐butanol in the interfacial layer first increased sharply and then tended to be stable with the addition of n‐butanol. For the different optimum W‐III microemulsion systems tested, most of the surfactant‐to‐alcohol molar ratio data are near 1:3, but obvious deviation could be observed for some data. On the basis of the accurate measurement of n‐butanol content in the EO and EW phases, the standard free energy, ΔGo→in* (T = 298.15 K) of n‐butanol transferring from the EO phase to the interfacial region was calculated. The results show negative ΔGo→in* values. For microemulsions with the same components, n‐butanol content is an important factor influencing the ΔGo→in* value, and a high absolute value of ΔGo→in* leads to high solubilization ability.