Solubilization of water by dialkyl sodium sulfosuccinates in hydrocarbon solutions

The apparent solubilization of water in hydrocarbon solvents by the addition of 0.1% to 2.0% w/w di-(2-ethylhexyl) sodium sulfosuccinate (AOT) has been studied. In n-octane and n-decane, transitions of clear-turbid-clear-turbid were observed with increasing water content, whereas in dodecane, tetradecane, hexadecane, cyclohexane, and toluene only one clear-turbid transition was seen. Separation of the first turbid region in n-octane and n-decane gave two clear phases. Direct analysis indicates a hydrocarbon phase containing surfactant-solubilized water and an aqueous phase containing some surfactant. Increasing amounts of water partition between these phases until a second clear region appears. Separation of phases in the second turbid region in n-octane and n-decane and in the turbid region of the other solvents produces a pure hydrocarbon phase and a phase containing a complex aggregate of AOT/water/hydrocarbon. Solubilization of water in n-octane solutions of di-(n-octyl) sodium sulfosuccinate and di-(n-hexyl) sodium sulfosuccinate is greatly reduced when compared to AOT. This suggests a significant effect due to the ethyl side chain in the AOT molecule.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33042/1/0000428.pd

The Influence of Short-Chain Alcohols on Interfacial Tension, Mechanical Properties, Area/Molecule, and Permeability of Fluid Lipid Bilayers

We used micropipette aspiration to directly measure the area compressibility modulus, bending modulus, lysis tension, lysis strain, and area expansion of fluid phase 1-stearoyl, 2-oleoyl phosphatidylcholine (SOPC) lipid bilayers exposed to aqueous solutions of short-chain alcohols at alcohol concentrations ranging from 0.1 to 9.8 M. The order of effectiveness in decreasing mechanical properties and increasing area per molecule was butanol>propanol>ethanol>methanol, although the lysis strain was invariant to alcohol chain-length. Quantitatively, the trend in area compressibility modulus follows Traube's rule of interfacial tension reduction, i.e., for each additional alcohol CH(2) group, the concentration required to reach the same area compressibility modulus was reduced roughly by a factor of 3. We convert our area compressibility data into interfacial tension values to: confirm that Traube's rule is followed for bilayers; show that alcohols decrease the interfacial tension of bilayer-water interfaces less effectively than oil-water interfaces; determine the partition coefficients and standard Gibbs adsorption energy per CH(2) group for adsorption of alcohol into the lipid headgroup region; and predict the increase in area per headgroup as well as the critical radius and line tension of a membrane pore for each concentration and chain-length of alcohol. The area expansion predictions were confirmed by direct measurements of the area expansion of vesicles exposed to flowing alcohol solutions. These measurements were fitted to a membrane kinetic model to find membrane permeability coefficients of short-chain alcohols. Taken together, the evidence presented here supports a view that alcohol partitioning into the bilayer headgroup region, with enhanced partitioning as the chain-length of the alcohol increases, results in chain-length-dependent interfacial tension reduction with concomitant chain-length-dependent reduction in mechanical moduli and membrane thickness