Solubilization of medium-chained alcohols in some ENORDET O series surfactants

Abstract

Primary to tertiary pentanol and -hexanol in Shell Chemicals' ENORDET O series IOS 1923, and for primary pentanol in IOS 2024, have been investigated by a thermodynamic approach. Standard partial molar volume and isentropic compressibility in micellar phase, as well as mole-fraction based distribution, are determined and used for interpretation. The experimental part of this investigation include determining density and speed of sound in various concentration of alcohol and surfactant in water. Standard partial molar properties reveal presence of mixed hydrophilic-hydrophobic interactions for alcohols in micellar phase of IOS. Distribution for alcohols is less in both IOS surfactants compared to reported values of SDS, and results suggest solubilized alcohols are on average experiencing a less hydrophobic environment in IOS 1923 compared to in SDS. The contrary is observed for 1-pentanol solubilized in IOS 2024, where the average solubilization environment seem more hydrophobic relative to in SDS. These observations may, at least in parts, be reasoned by considering the nature of the IOS surfactants. Substituting hydroxyl group from primary to tertiary position on pentanol and on hexanol in IOS 1923 reveal some similarities with trends observed in SDS. However abnormalities are observed. Variation in solubilization parameters among IOS 1923 and IOS 2024 does not correspond well with observations of varying surfactant chain length in model surfactants. This may be due to dissimilarities in IOS samples overriding this effect.