Evidence of dynamic crossover phenomena in water and other glass-forming liquids: experiments, MD simulations and theory
Evidence of dynamic crossover phenomena in water and other glass-forming liquids: experiments, MD simulations and theory
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DOI：
10.1088/0953-8984/21/50/504102
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发表时间：
2009-12-16
影响因子：
2.7
通讯作者：
Mallamace, F.
中科院分区：
文献类型：
--
作者：
Chen, S. H.;Zhang, Y.;Mallamace, F.
在最近对硅酸盐水泥膏体中承压水的准弹性中子散射实验中，我们发现这种三维承压水在T-L = 227 +/- 5 K时表现出动态交叉现象。冷却时的DSC热流扫描和硅胶中承压水的恒压比热的独立测量显示，在相同温度下有一个显著的峰值。我们在本文中表明，这种行为在许多其他玻璃液体中是常见的，它们也显示交叉温度与小比热峰的温度一致。我们还通过MD模拟证明了承压水中的动态交叉现象是散装水的固有性质，而不是由于约束效应。近年来，提出了一种包含跳频效应的模式耦合理论的扩展版本。该理论表明，理想MCT预测的T-C处不是结构阻滞转变，而是在T-C处发生了脆弱到强的动态交叉现象，证实了实验和数值结果。相干和非相干α弛豫时间可以与计算的粘度成比例，显示出相同的交叉现象。因此，我们通过实验、模拟和理论证明，在交叉温度T-L下，水和许多玻璃状液体的动力学行为发生了真正的变化，该温度比量热玻璃转变温度T-g高10-30%。
In a recent quasi-elastic neutron scattering experiment on water confined in a Portland cement paste, we find that this 3D confined water shows a dynamic crossover phenomenon at T-L = 227 +/- 5 K. The DSC heat-flow scan upon cooling and an independent measurement of specific heat at constant pressure of confined water in silica gel show a prominent peak at the same temperature. We show in this paper that this type of behavior is common to many other glassy liquids, which also show the crossover temperature in coincidence with the temperature of a small specific heat peak. We also demonstrate with MD simulations that the dynamic crossover phenomenon in confined water is an intrinsic property of bulk water, and is not due to the confinement effect. Recently, an extended version of the mode coupling theory (MCT) including the hopping effect was developed. This theory shows that, instead of a structural arrest transition at T-C predicted by the idealized MCT, a fragile-to-strong dynamic crossover phenomenon takes place instead at T-C, confirming both the experimental and the numerical results. The coherent and incoherent alpha relaxation times can be scaled with the calculated viscosity, showing the same crossover phenomenon. We thus demonstrated with experiments, simulations and theory that a genuine change of dynamical behavior of both water and many glassy liquids happens at the crossover temperature T-L, which is 10-30% higher than the calorimetric glass transition temperature T-g.