拉伸条件下水中空化的分子机理
Molecular mechanism for cavitation in water under tension
摘要：
尽管它在生物学和工程学中具有相关性，但驱动水中空化的分子机制仍然未知。利用计算机模拟，我们调查的结构和动力学的汽泡出现在亚稳态水在负压。我们发现，在空化的早期阶段，气泡是不规则的形状，并成为更多的球形，因为它们的增长。然而，气泡形成的自由能可以完美地再现在经典成核理论（CNT）的框架内，如果考虑曲率依赖的表面张力。宏观瑞利-Plesset（RP）方程，增强与热波动的预测，所观察到的气泡动力学的比较表明，纳米级气泡的生长是由粘性力。结合从RP方程与CNT的自由能确定的动态前因子产生的空化率，再现模拟结果非常好的在很宽的压力范围内的解析表达式。此外，我们的理论预测是在良好的协议从夹杂物实验获得的空化率。这表明在夹杂物中观察到均质成核，而在其他实验中仅发生在杂质或缺陷上的异相成核。
英文摘要：
Despite its relevance in biology and engineering, the molecular mechanism driving cavitation in water remains unknown. Using computer simulations, we investigate the structure and dynamics of vapor bubbles emerging from metastable water at negative pressures. We find that in the early stages of cavitation, bubbles are irregularly shaped and become more spherical as they grow. Nevertheless, the free energy of bubble formation can be perfectly reproduced in the framework of classical nucleation theory (CNT) if the curvature dependence of the surface tension is taken into account. Comparison of the observed bubble dynamics to the predictions of the macroscopic Rayleigh--Plesset (RP) equation, augmented with thermal fluctuations, demonstrates that the growth of nanoscale bubbles is governed by viscous forces. Combining the dynamical prefactor determined from the RP equation with the free energy of CNT yields an analytical expression for the cavitation rate that reproduces the simulation results very well over a wide range of pressures. Furthermore, our theoretical predictions are in excellent agreement with cavitation rates obtained from inclusion experiments. This suggests that homogeneous nucleation is observed in inclusions, whereas only heterogeneous nucleation on impurities or defects occurs in other experiments.
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