Effect of interfacial alcohol concentrations on oil solubilization by sodium dodecyl sulfate micelles

Alcohol partitioning and its effect on oil solubilization in Winsor Type I microemulsion systems was investigated. The microemulsion systems consisted of sodium dodecyl sulfate (SDS), pentanol, isopropanol (IPA), and dodecane , with either deionized water or an aqueous solution of 50 mM CaCl2. Alcoho l partitioning between aqueous, oil, and interfacial phases of the microemu lsion was described using a pseudophase model in which the alcohol was assu med to self-associate in the oil phase. Partitioning in these miroemulsions was consistent with pentanol self-association in the oil phase. IPA did no t self-associate but co-associated with pentanol in the oil phase. IPA conc entrations as high as 20 g/kg of water had no effect on pentanol partitioni ng. The partition coefficient for pentanol between aqueous and interfacial phases was about 220 on a mole fraction basis. However, pentanol saturated the interfacial phase at a mole ratio of 3 : 1 pentanol to SDS. Addition of pentanol beyond that sufficient to saturate the interface resulted in larg e amounts of pentanol partitioning into the oil, reaching concentrations in excess of 25 g dL(-1) of oil phase. Dodecane solubilization increased line arly with pentanol mole fraction in the interface up to the 3:1 pentanol-to -SDS saturation level. The fact that dodecane solubilization was unaffected by pentanol at concentrations beyond those necessary for interfacial satur ation suggests that pentanol behaves as a cosurfactant and not a cosolvent in these microemulsion systems, (C) 2000 Academic Press.