Montero de Hijes P, Espinosa J R, Vega C, Sanz E
Departamento de Química Física, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain.
Maxwell Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, United Kingdom.
J Chem Phys. 2019 Jul 28;151(4):044509. doi: 10.1063/1.5103273.
The transformation of liquid water into solid ice is arguably the most important phase transition on Earth. A key aspect of such transformation is the speed with which ice grows once it is nucleated. There are contradictory experimental results as to whether the ice growth rate shows a maximum on cooling. Previous simulation results point to the existence of such a maximum. However, simulations were performed at constant temperature with the aid of a thermostat that dissipates the heat released at the ice-water interface unrealistically fast. Here, we perform simulations of ice growth without any thermostat. Large systems are required to perform these simulations at constant overall thermodynamic conditions (pressure and temperature). We obtain the same growth rate as in previous thermostatted simulations. This implies that the dynamics of ice growth is not affected by heat dissipation. Our results strongly support the experiments predicting the existence of a maximum in the ice growth rate. By using the Wilson-Frenkel kinetic theory, we argue that such maximum is due to a competition between an increasing crystallization thermodynamic driving force and a decreasing molecular mobility on cooling.
液态水转变为固态冰可以说是地球上最重要的相变。这种转变的一个关键方面是冰一旦成核后的生长速度。关于冰生长速率在冷却时是否存在最大值，存在相互矛盾的实验结果。先前的模拟结果表明存在这样一个最大值。然而，模拟是在恒温条件下借助恒温器进行的，该恒温器以不切实际的速度消散冰水界面释放的热量。在这里，我们在没有任何恒温器的情况下进行冰生长模拟。需要大型系统才能在恒定的整体热力学条件（压力和温度）下进行这些模拟。我们获得了与先前恒温模拟相同的生长速率。这意味着冰生长的动力学不受热耗散的影响。我们的结果有力地支持了预测冰生长速率存在最大值的实验。通过使用威尔逊 - 弗伦克尔动力学理论，我们认为这种最大值是由于冷却时结晶热力学驱动力增加与分子迁移率降低之间的竞争所致。
