Temporal changes of the weight, volume, temperature and elastic properties during the dehydration process of a polyacrylamide (PAAm) gel were studied. Both the weight and the volume monotonically decreased in the early stage of the process and then tended to saturate in the late stage. At the crossover point between these two dependencies, the temperature of the gel and its elastic stiffness showed anomalies, which indicated similar aspects to the glass transition often observed in non-crystalline polymers. The water content in gels is an important factor affecting the transition.
Raman scattering experiment was carried out simultaneously with weight measurement during the dehydration process of polyacrylamide (PAAm) gel. Anomalies in the Raman spectrum were observed when the time dependence of the weight altered: around the first characteristic time, a shoulder emerged on the skirt of the low-lying diffusive central mode, and then around the second one, the shoulder changed into a peak (which resembled the “boson peak" commonly observed in glass) in addition to the disappearance of the central diffusive mode and an O–H stretching mode. The correlation between the spectral change and the time dependence of the weight demonstrated the effect of increase in the polymer chain interaction on the gel's dynamical properties.
Left in a dry. atmosphere for a while, gels become glasslike dehydrated substances. We investigated the dehydration process of some gels by adopting simultaneous time-resolved measuring method of weight and other properties. The feature during the dehydration process was different depending on the properties of the network and solvent in gel. Besides, in the DTA measurements of the dehydrated egg white gel, we observed an endothermic peak of which the intensity and peak position increased with elevating heating rate, similar to the glass transition in the non-crystalline polymers.
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