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标题：Visualization of Freezing Process in situ upon Cooling and Warming of Aqueous Solutions
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作者：Anatoli Bogdan ; Mario J. Molina ; Heikki Tenhu 等
期刊名称：Scientific Reports
电子版ISSN：2045-2322
出版年度：2014
卷号：4
DOI：10.1038/srep07414
出版社：Springer Nature
摘要：The freezing of aqueous solutions and reciprocal distribution of ice and a freeze-concentrated solution (FCS) are poorly understood in spite of their importance in fields ranging from biotechnology and life sciences to geophysics and climate change. Using an optical cryo-miscroscope and differential scanning calorimetry, we demonstrate that upon cooling of citric acid and sucrose solutions a fast freezing process results in a continuous ice framework (IF) and two freeze-concentrated solution regions of different concentrations, FCS₁ and FCS₂. The FCS₁ is maximally freeze-concentrated and interweaves with IF. The less concentrated FCS₂ envelops the entire IF/FCS₁. We find that upon further cooling, the FCS₁ transforms to glass, whereas the slow freezing of FCS₂ continues until it is terminated by a FCS₂-glass transition. We observe the resumed slow freezing of FCS₂ upon subsequent warming. The net thermal effect of the resumed freezing and a reverse glass-FCS₁ transition produces the T_tr2 -transition which before has only been observed upon warming of frozen hydrocarbon solutions and which nature has remained misunderstood for decades.