IDENTIFICATION OF THERMOTROPIC PHASE-TRANSITIONS OF GLYCERYL MONOOLEIN-WATER SYSTEMS BY LOW-FREQUENCY DIELECTRIC-SPECTROSCOPY

Thermotropic phase transitions of glyceryl monoolein-water systems hav e been investigated using dielectric spectroscopy over a frequency ran ge of 10(-2)-10(6) Hz and a temperature range of 15-100 degrees C, and also using differential interference contrast (DIC) microscopy fitted with a hot stage as a support technique. The frequency and temperatur e dependencies of the dielectric permittivity of systems undergoing tr ansitions between lamellar, cubic, reverse hexagonal and L-2 phases ar e reported. It was demonstrated that the frequency dependent response is highly sensitive to changes in phase and a model is described which allows the dielectric behaviour to be interpreted in terms of an equi valent circuit diagram, thereby allowing the response to be related to specific structural features within the sample. Similarly, it was dem onstrated that the phase transition temperatures and ranges could be i dentified using the dielectric technique, yielding results which were in good agreement with those obtained using DIC microscopy for those s ystems whereby the phase changes are optically identifiable. The study therefore suggests that low frequency dielectric analysis is a potent ially highly useful tool for the identification of thermotropic phase changes. (C) 1998 Elsevier Science B.V. All rights reserved.