Water's second glass transition
Water's second glass transition
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DOI：
10.1073/pnas.1311718110
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发表时间：
2013-10-29
影响因子：
11.1
通讯作者：
Loerting, Thomas
中科院分区：
文献类型：
--
作者：
Amann-Winkel, Katrin;Gainaru, Catalin;Loerting, Thomas
玻璃水状态具有共同的关注液体。多年来，由于其量热的签名非常微弱，因此有争议地讨论了Water在136 K处的低密度无定形冰的量热玻璃过渡的发生。在这里，我们报告说，在环境压力下的高密度无定形冰显示在116 K处的量热玻璃转变，并有证据表明第二个玻璃转变涉及水分子的液体样转化迁移率。这种“双TG场景”与两个液相的共存有关。第二玻璃过渡的量热标志的量牌较小得多，TG-2的热容量大约是TG-1的五倍。通过使用宽带二仪光谱法，我们可以解决低密度无定形冰时在126 K时在126 K处产生弛豫时间的损失峰，而高密度无定形冰的损失峰为这两个不同的玻璃转换的特征。依赖温度的介电数据和取暖率依赖性的量热数据使我们能够为水的两个不同阶段构建弛豫图，并为低密度提取脆弱性指数M = 14，高密度为M = 20-25密度液体。因此，低密度液体被归类为所有已知液体中最强的液体（“ superstrong”），并且高密度液体也被归类为强液。
The glassy states of water are of common interest as the majority of H2O in space is in the glassy state and especially because a proper description of this phenomenon is considered to be the key to our understanding why liquid water shows exceptional properties, different from all other liquids. The occurrence of water's calorimetric glass transition of low-density amorphous ice at 136 K has been discussed controversially for many years because its calorimetric signature is very feeble. Here, we report that high-density amorphous ice at ambient pressure shows a distinct calorimetric glass transitions at 116 K and present evidence that this second glass transition involves liquid-like translational mobility of water molecules. This "double Tg scenario" is related to the coexistence of two liquid phases. The calorimetric signature of the second glass transition is much less feeble, with a heat capacity increase at Tg-2 about five times as large as at Tg-1. By using broadband-dielectric spectroscopy we resolve loss peaks yielding relaxation times near 100 s at 126 K for low-density amorphous ice and at 110 K for high-density amorphous ice as signatures of these two distinct glass transitions. Temperature-dependent dielectric data and heating-rate-dependent calorimetric data allow us to construct the relaxation map for the two distinct phases of water and to extract fragility indices m = 14 for the low-density and m = 20-25 for the high-density liquid. Thus, low-density liquid is classified as the strongest of all liquids known ("superstrong"), and also high-density liquid is classified as a strong liquid.