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

Frozen aqueous solutions were studied using dynamic mechanical spectro metry. DMTA measurements required different devices because of the lar ge evolution of the theological behavior of the mixtures with temperat ure, 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 soften ing was due to a glass transition of the amorphous fraction. The tempe rature range, where it is observed, corresponds well to the beginning of the two-step thermal feature observed by differential scanning calo rimetry before the ice melting. Compression tests have a better sensit ivity at low temperatures but only shear tests allow one to make a ful l examination of the sample changes during the glass transition of the amorphous phase, and then the ice melting, during the heating process .