超冷水和玻璃态水的热力学性质新探

Water's most pronounced anomalies, e.g., glass-liquid transition and liquid-liquid phase transition, are believed hiding in the crystallization region at low temperatures. It has been a long challenge for scientist to take a deep insight into this region. Recent studies have demonstrated the possibility of avoiding water crystallization at deep cooling in nanoscale confinements; however, this way inevitably introduces uncertainties, e.g., surface effects, into the targeted system, and leads to extensive debate. Here, we propose an alternative approach by using fibrous glassy water with diameters of submicron (we have invented this method). DSC tests show no clear sign of crystallization at temperatures up to 0℃, but two endothermic peaks near T1=136 K，T2=230 K, referring to the glass-liquid transition and liquid-liquid phase transition, respectively. Mechanical experiments also demonstrate the presence of three distinct regions: elastic (T<T1), high viscosity (T1 <T<T2) and low viscosity (T>T2). These results explicitly indicate that this new approach is effective to avoid water crystallization at no costs of losing its fundamental properties. Therefore, we strongly propose that a systematic evaluation of water's properties under the new approach need to be done so as to understand its full thermodynamic picture. This project will also shed light on the properties of confined and interfacial water.

水的一些最重要特性，如玻璃化转变和液-液相变，被怀疑隐藏在结晶区域里。长期以来，如何突破结晶屏障一直是困扰科学家们的棘手问题。最新研究显示受限于纳米空间的水可避免在低温下结晶，然而，相关结果的可靠性和代表性受到了强烈质疑。在此，我们提出一个全新的解决方案，即采用具有亚微米直径的、纤维状的、非受限的玻璃态水作为液态水低温热力学性质的研究体系（我们已发明了相应制作方法）。DSC测试结果表明，该玻璃态水在升温过程中没有出现明显的结晶，但在T1=136 K，T2=230 K附近清晰地呈现两个吸热峰，分别表现出玻璃化转变和液-液相变的特征。力学形变结果也表明该玻璃态水存在三个明显不同的力学状态：弹性态（T<T1），高粘态（T1<T<T2），低粘态（T>T2）。因此，进一步的深入研究对掌握目前具有广泛争议的水的低温热力学性质具有重大科学意义，同时，对阐明受限水和表面水的基本性质提供重要参考。

长期以来，水在低温下的一些重要热力学特性，如玻璃化转变和液-液相变等，被怀疑掩藏在结晶区域中。为此，我们突破了水的结晶屏障，自主搭建了静电喷雾和低温猝冷设备平台。利用该平台，我们成功将水制备成具有纳米尺寸、纤维状、非受限的液态水，同时对其形成条件和控制参数的进行了多方面的探索，并提出了可能的形成机理。我们认为一维非受限液态水是由电喷雾过程中下落液滴所挥发出的蒸气在低温和电场作用下凝聚而成，形成机理包括液滴挥发，蒸气过饱和，液滴凝聚，低温猝冷四个物理过程。我们以所得的一维非受限液态水的热力学性质为研究对象，通过现代光谱学和热力学测试手段，系统的表征了其在低温区的性质。结果表明，该研究对象在免于结晶的同时，又能够不损失体相水的基本属性，这一发现对掌握目前具有广泛争议的水的低温热力学性质具有较大的科学意义，对阐明受限水和表面水的基本性质将提供重要参考。