Phase behaviour of monoglyceride/water systems

Abstract

Studies on the gel and lamellar phases formed by C16–18 saturated monoglyceride, C16–18SMG (Hymono 8903, a commercial distilled monoglyceride) in contact with water are described. Optical microscopy was used to study the mesomorphic behaviour as a function of temperature. Differential scanning calorimetry was utilised to determine the transition enthalpies between the mesophases. Surfactant mobility was studied by measuring proton NMR T2 relaxation times for samples comprising C16–18SMG/2H2O. Molecular ordering was also studied by measuring 2H and 17O quadrupole splittings (by NMR) for systems comprising C16–18SMG/2H2O and C16–18SMG/H217O (10% H217O in H216O).Over the temperature range studied (0–90 °C), gel, lamellar and cubic mesophases were found. For the gel phase, separate 2H NMR spectra, representing the 2H2O solvent and the monoglyceride O2H groups, were observed. Two signals were also observed for the lamellar phase. From the relative intensities, one signal was assigned to the O2H group on the terminal carbon atom of the monoglyceride molecule, whilst the other signal arose from the 2H2O solvent and the other monoglyceride O2H group. Analysis of these results demonstrate that there are about three bound water molecules per surfactant molecule for the lamellar phase at maximum hydration. Unusually, the degree of ordering of the water in the gel phase is much smaller than that of the water in the lamellar phase.