Department of Chemistry, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5C9, Canada.
J Chem Phys. 2011 Mar 21;134(11):114505. doi: 10.1063/1.3565479.
The heterogeneous condensation of a Lennard-Jones vapor onto a nanoscale seed particle is studied using molecular dynamics simulations. Measuring the nucleation rate and the height of the free energy barrier using the mean first passage time method shows that the presence of a weakly interacting seed has little effect on the work of forming very small cluster embryos but accelerates the rate by lowering the barrier for larger clusters. We suggest that this results from a competition between the energetic and entropic features of cluster formation in the bulk and at the heterogeneity. As the interaction is increased, the free energy of formation is reduced for all cluster sizes. We also develop a simple phenomenological model of film formation on a small seed that captures the general features of the nucleation process for small heterogeneities. A comparison of our simulation results with the model shows that heterogeneous classical nucleation theory provides a good estimate of the critical size of the film but significantly overestimates the size of the barrier.
采用分子动力学模拟研究了 Lennard-Jones 蒸汽在纳米尺度种子颗粒上的非均匀凝结。使用平均首通过时法测量成核速率和自由能垒高度表明，弱相互作用的种子的存在对形成非常小的团簇胚胎的功几乎没有影响，但通过降低较大团簇的势垒来加速速率。我们认为这是由于在本体和异质相中团簇形成的能量和熵特征之间的竞争所致。随着相互作用的增加，所有团簇尺寸的形成自由能都会降低。我们还开发了一种简单的小种子上薄膜形成的唯象模型，该模型捕获了小非均相核化过程的一般特征。我们的模拟结果与模型的比较表明，异质经典成核理论很好地估计了薄膜的临界尺寸，但大大高估了势垒的尺寸。
