EFFECT OF ALKYL SULFATES ON THE PHASE-BEHAVIOR AND MICROSTRUCTURE OF ALKYL POLYGLUCOSIDE MICROEMULSIONS

The effects of adding alkyl sulfate surfactants to water-n-alkyl beta- D-glucopyranoside (C(m)beta G(1)) and water-alkyl ethylene glycol ethe r (CkOC2OCk)-C(m)beta G(1) mixtures are systematically explored. In a water-C(10)beta G(1)-sodium decyl sulfate (SDeS) mixture, miniscule am ounts of SDeS (SDeS:C(10)beta G(1) molar ratio of 0.0025) cause the up per miscibility gap of the water-C(10)beta G(1) mixture to vanish. Add ing small amounts of alkyl sulfates to water-CkOC2OCk-C(m)beta G(1) mi xtures increases the surfactant efficiency, shifts the single-phase mi croemulsion region to higher temperatures, and shrinks the three-phase region. These phenomenological phase behavior observations are explai ned in terms of electrostatic effects introduced by the addition of an ionic surfactant to nonionic micelles and monolayers. Small-angle neu tron scattering (SANS) measurements from several D2O-CkOC2OCk-C(m)beta G(1)-alkyl sulfate mixtures containing equal amounts of D2O and CkOC2 -OCk are analyzed using a model for bicontinuous microemulsions. The v alues obtained from this analysis show that the monolayer spacing of D 2O-CkOC2OCk-C(m)beta G(1)-alkyl sulfate mixtures grows with increasing ionic surfactant concentration, and this increased spacing accounts f or the observed increase in surfactant mixture efficiency.