Physical−Chemical Properties of the n-Octyl β-d-Glucoside/Water System. A Phase Diagram, Self-Diffusion NMR, and SAXS Study

Abstract

The n-octyl β-d-glucoside/water binary phase diagram (temperature vs concentration) and the aggregation parameters of the individual phases have been determined. n-Octyl β-d-glucoside forms four different phases together with water. At temperatures below 22 °C, there is an isotropic solution region from neat water extending up to almost 60 wt % n-octyl β-d-glucoside. As the concentration is further increased, three liquid crystalline phases form in the following order: hexagonal, cubic, and lamellar. At high surfactant concentrations (>93 wt %) the lamellar phase is in equilibrium with hydrated crystals. The hexagonal phase disappears at temperatures slightly higher than 20 °C. The solution region has been investigated with 1H-NMR to deduce the self-diffusion coefficients of both n-octyl β-d-glucoside and water. From these results it has been possible to draw conclusions about the surfactant aggregation behavior at dilute concentrations and when the n-octyl β-d-glucoside concentration is increased. The water diffusion in the n-octyl β-d-glucoside/water system has been compared with the diffusion process of water in a glucose solution, and it has been possible to interpret the data in terms of water diffusion in a glucose solution with some additional obstruction effects from the micellar hydrocarbon cores. The liquid crystalline phases have been examined by means of small-angle X-ray scattering and analyzed in terms of repetition distances and area/head group in the hexagonal, cubic, and lamellar phases. An important result of this study is the fact that the area per glucose unit in the surfactant is an almost invariant quantity across the phase diagram.

Aggregation Behavior of Sugar Surfactants in Aqueous Solutions: Effects of Temperature and the Addition of Nonionic Polymers

“…The sugar surfactant micelles should therefore be anisotropic. Such a conclusion would be in line with those of X-ray and neutron scattering studies of DM micelles (44,46) and NMR selfdiffusion studies of OG (21). But if it were so, the theory predicts that the DM micelles should be polydisperse (47), in contradiction with the TRFQ results which suggest monodisperse DM micelles, and with the weak dependence of N on concentration found for Hecameg micelles.…”

“…Thus, the effect of temperature on the behavior of the sugar surfactant micelles investigated differs much from that of C m E n micelles. This difference in behavior may be related to the phase diagrams of DM (7) and OG (21), which exhibit a large isotropic micellar range over a wide range of concentration (up to 45% for DM and 60% for OG) and temperature (up to 100°C) and show no clouding temperature (7,21). The absence of clouding and phase separation indicates that the intermicellar interactions are never strongly attractive, contrary to the situation in C m E n solutions.…”

“…Exchanges via intermicellar collisions usually take place in systems with attractive intermicellar interactions, such as the C m E n solutions (23)(24)(25). For OG and DM, the absence of a cloud curve in the phase diagram (7,21) indicates weak intermicellar interactions. In fact, Kameyama and Takagi (16) reported repulsive intermicellar interactions in OG solutions at high T. Besides, exchanges through collisions should also have been observed with DM.…”

The Effect of Anomeric Head Groups, Surfactant Hydrophilicity, and Electrolytes onn-Alkyl Monoglucoside Microemulsions

“…There are no upper miscibility gaps in these water-C m ␣G 1 mixtures, but Krafft boundaries exist at 39.5°C for C 8 ␣G 1 and at 43.5°C for C 9 ␣G 1 over the measured concentration range. Otherwise, these surfactants are completely miscible with water except for liquid crystalline regions at high surfactant concentrations (not measured) (6).…”

Acoustical Spectroscopy of Carbohydrate Aqueous Solutions: Saccharides; Alkyl Glycosides; Cyclodextrins. Part II. Association and Complexation

“…Besides synthesis optimization, most work has been devoted to phase diagrams and the structure of different phases of alkyl glycoside solutions (Nickel et al, 1993;Platz et. al., 1995;Bonicontro et al, 1996;Nilsson et al, 1996;Bonicelli et al, 1998;Schulte et al, 1999;Häntschel et al, 1999;Bogusz et al, 2000). The kinetics of self-aggregation, however, has been far less regarded.…”