Unusually Large Deuterium Isotope Effects in the Phase Diagram of a Mixed Alkylglucoside Surfactant/Water System

Mixtures of n -decyl-β- d -glucoside (C 10 G 1 ) and n -nonyl-β- d -glucoside (C 9 G 1 ) with liquid−liquid closed-loop miscibility gaps display a large deuterium isotope effect when D 2 O is substituted for H 2 O, 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 the surfactant in D 2 O and the effect of changes in the hydrogen bond strengths and lengths due to the exchange of O−H for O−D bonds in the glucose headgroups on the spontaneous curvature of the surfactant film.