Unusually large deuterium isotope effects in the phase diagram of a mixed alkylglucoside surfactant/water system

Mixtures of n-decyl-beta -n-glucoside (C(10)G(1)) and n-nonyl-beta-(D)-gluc oside (C(9)G(1)) with liquid-liquid closed-loop miscibility gaps display a large deuterium isotope effect when D2O is substituted for H2O, as seen by large shifts in both the critical points and phase boundaries. The observed isotope effect is larger than any previously seen in a surfactant system. It is' suggested that this is:due to both the increased hydrophobicity of t he surfactant in D2O and the effect of changes in the hydrogen bond strengt hs and lengths due to the exchange of O-H for O-D bonds in the glucose head groups on the spontaneous curvature of the surfactant film.