Colloid Polym Sci 276 : 109—116 (1998)  Steinkopff Verlag 1998 ORIGINAL CONTRIBUTION M.G. Bonicelli G.F. Ceccaroni C. La Mesa Lyotropic and thermotropic behavior of Alkylglucosides and related compounds Received: 15 May 1997 Accepted: 08 September 1997 C. La Mesa ( ) Dipartimento di Chimica Universita´ ‘‘La Sapienza’’ Roma, Italia M.G. Bonicelli Dipartimento I.C.M.M.P.M. Universita´ ‘‘La Sapienza’’ Roma, Italia G.F. Ceccaroni Dipartimento Tecnol. Chimiche Universita´ ‘‘Tor Vergata’’ Roma, Italia Abstract The phase diagram of the binary system composed of octyl--D- glucopyranoside and water was investigated and the phase boundaries were determined. Polarising optical microscopy was used to define the different phases, proton and deuterium NMR experiments to define the region of existence of the different phases and to obtain information on axiality and head group solvation. DSC experiments were performed to determine the thermal transitions from solid to thermotropic liquid crystals for octyl- -D-gluco-pyranoside, the related alkylglucosides or maltosides, and to gain information on the role played by sugar units in the thermodynamics of such phase transitions. Key words: Surfactants — alkylglucosides — phase equilibria — micelles — lyotropic liquid crystals — thermotropic liquid crystals. Introduction The discovery of the mesomorphic behavior is strictly related to studies on alkylated carbohydrates. On analys- ing the extracts from tuberculosis bacteria Koch observed unusual optical textures of their aqueous dispersions [1], whereas Fischer observed double melting phenomena in dry alkylpryanosides [2]. These studies are considered the first contributions on lyotropic and thermotropic behav- ior, respectively. Alkyl glucosides (AGs) are known since long times and information is available on their thermotropic behavior [3, 4]. No efforts have been made to link the thermotropic and lyotropic properties, although these substances form micelles and lyotropic liquid crystals [5—10]. Concerning the polymorphic behavior of AGs in solu- tion, the crystalline order in gels and solutions of N-octyl- gluconamide [9], the mesomorphic phases of N-alkyl lactosylamines [10] and the phase diagram of octyl-- D-gluco pyranoside, OG, and of its thio homologue have been reported [7, 8]. The solution properties of OG have been previously reported and information on micelle formation and aggregate size, shape and hydra- tion is available [8, 11—14]. Much less known are the solution properties of its homologues, but studies on solu- tions of octyl-thio--D-gluco-pyranoside, decyl--D-gluco- pyranoside, and decyl--maltoside have been recently performed [15]. Because of their molecular properties, the occurrence of an hydrogen-bond network between the sugar units is expected. It stabilizes the thermotropic phases and plays a role in lyotropic and solution phases. To clarify still open questions, we report on the phase equilibria for two alkyl glucosides, a structurally related thioglucoside and a maltoside. GL 916