McGraw Robert L, Winkler Paul M, Wagner Paul E
Environmental, and Climate Sciences Department, Brookhaven National Laboratory, Upton, NY, 11973, USA.
University of Vienna, Faculty of Physics, Vienna, Austria.
Sci Rep. 2017 Dec 4;7(1):16896. doi: 10.1038/s41598-017-16692-9.
A re-examination of measurements of heterogeneous nucleation of water vapor on silver nanoparticles is presented here using a model-free framework that derives the energy of critical cluster formation directly from measurements of nucleation probability. Temperature dependence is correlated with cluster stabilization by the nanoparticle seed and previously found cases of unusual increasing nucleation onset saturation ratio with increasing temperature are explained. A necessary condition for the unusual positive temperature dependence is identified, namely that the critical cluster be more stable, on a per molecule basis, than the bulk liquid to exhibit the effect. Temperature dependence is next examined in the classical Fletcher model, modified here to make the energy of cluster formation explicit in the model. The contact angle used in the Fletcher model is identified as the microscopic contact angle, which can be directly obtained from heterogeneous nucleation experimental data by a recently developed analysis method. Here an equivalent condition, increasing contact angle with temperature, is found necessary for occurrence of unusual temperature dependence. Our findings have immediate applications to atmospheric particle formation and nanoparticle detection in condensation particle counters (CPCs).
本文使用一种无模型框架对银纳米颗粒上水蒸气异质成核的测量进行了重新审视，该框架直接从成核概率测量中推导临界团簇形成的能量。温度依赖性与纳米颗粒种子对团簇的稳定作用相关，并解释了先前发现的随着温度升高成核起始饱和比异常增加的情况。确定了异常正温度依赖性的必要条件，即在每个分子基础上，临界团簇比本体液体更稳定才能表现出这种效应。接下来在经典的弗莱彻模型中研究温度依赖性，在此对该模型进行了修改，使团簇形成的能量在模型中明确体现。弗莱彻模型中使用的接触角被确定为微观接触角，可通过最近开发的分析方法直接从异质成核实验数据中获得。在此发现，对于异常温度依赖性的出现，一个等效条件是接触角随温度增加。我们的研究结果在大气颗粒物形成和冷凝粒子计数器（CPC）中的纳米颗粒检测方面有直接应用。
