The Manifestation of Hysteresis in the Thermal Properties of Nanosystems Based on the Example of Supercooled Water Clusters in Wet Sephadex of the G Type

Autor: Ο. Ι. Smirnova, N. A. Grunina, T. V. Belopolskaya, G. I. Tsereteli
Rok vydání: 2020
Předmět:
Zdroj: Biophysics. 65:28-38
ISSN: 1555-6654
0006-3509
DOI: 10.1134/s0006350920010078
Popis: —The research cycle of thermal properties of water clusters in polysaccharide–water systems (starch and Sephadex G-100) with a low content of freezing water was continued based on the example of another modified polysaccharide, Sephadex G-25. This Sephadex has a more rigid three-dimensional structure compared with Sephadex G-100. The doublet structure of the melting curve of water clusters, which indicated the bimodal nature of their size distribution, was the main peculiarity of the data obtained for Sephadex G-25 by differential scanning calorimetry. The observed decrease in the temperature and heat of melting and crystallization of water clusters with a decrease in the humidity of Sephadex G-25, as in the case of other polysaccharides, was a typical manifestation of the size effect for nanosystems. At the same time, hysteresis occurred between the temperatures $$\Delta T = {{T}_{{{\text{mel}}}}} - {{T}_{{{\text{cr}}}}}$$, and the heats $$\Delta Q = {{Q}_{{{\text{mel}}}}} - {{Q}_{{{\text{cr}}}}}$$ of these transitions, which is also typical for small systems. It was found that the transformation processes (recrystallization, reorganization, and size change) in the system of clusters of crystallized supercooled water in Sephadex G-25 with low humidity during heating could occur both below the melting interval and inside it, which indicated the nonequilibrium state of the original set of nanoclusters. It was shown that the decrease of Vheat, as well as annealing within the melting interval led to a redistribution of clusters in size and, according to the revealed size effect, to an increase in the melting heat. These facts taken together indicated that the nonequilibrium state of the initially formed clusters during cooling and, as a consequence, their ability to transform with increasing temperature certainly play an important, if not a decisive, role in the manifestation of hysteresis in the thermal properties of water nanoclusters.
Databáze: OpenAIRE
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