Phase equilibria and physical-chemical properties of sugar-based surfactants in aqueous solutions

A study of solution properties of 3 nonionic surfactants derived from glucose is reported. These surfactants, from a series of 6-O-acyl-α,β-d-glucopyranoses, differ from one other by the number of carbon atoms in their alkyl chain: 6-O-decanoyl-, 6-O-stearoyl- and 6-O-oleyl-. The surface properties [critical micellar concentration (cmc) and minimal area/molecule at air-water interface (amin)] were investigated in water at 42 °C by means of surface tension measurements. Partial phase diagrams and liquid-crystalline mesophases were studied in heavy water using polarising microscopy, 2H-NMR spectra and DSC measurements. All binary systems form a lamellar lyomesophase in a wide range of composition. A Gel → Lamellar phase transition was observed as the temperature was increased only on the 6-O-decanoyl-d-glucopyranose/D2O system. The Gel-Lamellar transition temperatures were checked by DSC thermograms. Molecular self-diffusion of surfactant and water in the micellar solution phase of 6-O-decanoyl-d-glucopyranose/D2O system were determined at 35 °C by Fourier transform pulsed gradient spin-echo 1H-NMR spectroscopy. From this study it has been possible to draw conclusions about the changes on the solution microstructures as function of surfactant concentration.