RELIABILITY OF DYNAMIC-MECHANICAL THERMAL ANALYSES (DMTA) FOR THE STUDY OF FROZEN AQUEOUS SYSTEMS

Frozen aqueous solutions were studied using dynamic mechanical spectrometry. DMTA measurements required different devices because of the large evolution of the rheological behavior of the mixtures with temperature, particularly a strong decrease in rigidity during the melting of the ice. For stabilized frozen solutions in which the solutes were not able to crystallize, DMTA showed clearly that the beginning of softening was due to a glass transition of the amorphous fraction. The temperature range, where it is observed, corresponds well to the beginning of the two-step thermal feature observed by differential scanning calorimetry before the ice melting. Compression tests have a better sensitivity at low temperatures but only shear tests allow one to make a full examination of the sample changes during the glass transition of the amorphous phase, and then the ice melting, during the heating process. © 1985, The Society of Rheology. All rights reserved.