Effect of Alkyl Sulfates on the Phase Behavior and Microstructure of Alkyl Polyglucoside Microemulsions

Abstract

The effects of adding alkyl sulfate surfactants to water−n-alkyl β-d-glucopyranoside (CmβG1) and water−alkyl ethylene glycol ether (CkOC2OCk)−CmβG1 mixtures are systematically explored. In a water−C10βG1−sodium decyl sulfate (SDeS) mixture, miniscule amounts of SDeS (SDeS:C10βG1 molar ratio of 0.0025) cause the upper miscibility gap of the water−C10βG1 mixture to vanish. Adding small amounts of alkyl sulfates to water−CkOC2OCk−CmβG1 mixtures increases the surfactant efficiency, shifts the single-phase microemulsion region to higher temperatures, and shrinks the three-phase region. These phenomenological phase behavior observations are explained in terms of electrostatic effects introduced by the addition of an ionic surfactant to nonionic micelles and monolayers. Small-angle neutron scattering (SANS) measurements from several D2O−CkOC2OCk−CmβG1−alkyl sulfate mixtures containing equal amounts of D2O and CkOC2OCk are analyzed using a model for bicontinuous microemulsions. The values obtained from this analy...