INFIQC, Departamento de Matemática y Física, Facultad de Ciencias Químicas, UNC. Argentina.
Phys Chem Chem Phys. 2010 May 14;12(18):4580-9. doi: 10.1039/b924348h. Epub 2010 Mar 16.
Following the framework established by Hill and Chamberlin [T. L. Hill and R. V. Chamberlin, Proc. Natl. Acad. Sci. U. S. A., 1998, 95, 12779] to analyze the extension of thermodynamics of small systems to metastable states, we have adopted the same basic ideas to study the thermodynamic stability of core-shell nanoparticles. For the first time we are able to address the question of whether or not core-shell nanoparticles have a limit of stability when they are under oversaturation conditions. By the latter, we mean the excess of chemical potential of the adsorbate (shell) atoms with respect to its bulk material, which is the driving force for nanoparticle growth. In this situation the probability density exhibits multiple local maxima associated with different core-shell metastable states. The decrease of the free energy barriers for the growth of the bulk phase of the shell material is analyzed for increasing oversaturation. At large positive oversaturations, the barrier disappears and the core-shell NP become unstable with respect to the bulk deposit of the shell material. A brief discussion on the model is made illustrating its application to a specific system by means of computer simulations using realistic interatomic potentials. One of the most striking results of these specific studies is the occurrence or not of a core-shell under undersaturation conditions depending on nanoparticle size.
按照 Hill 和 Chamberlin [T. L. Hill 和 R. V. Chamberlin, Proc. Natl. Acad. Sci. U. S. A., 1998, 95, 12779]建立的分析小系统热力学向亚稳状态扩展的框架，我们采用了相同的基本思想来研究核壳纳米粒子的热力学稳定性。我们首次能够解决核壳纳米粒子在过饱和度条件下是否具有稳定性极限的问题。这里的过饱和度是指吸附剂（壳）原子的化学势相对于其体材料的过剩，这是纳米粒子生长的驱动力。在这种情况下，概率密度表现出与不同的核壳亚稳状态相关的多个局部最大值。分析了壳材料体相生长的自由能垒随过饱和度的增加而降低。在较大的正过饱和度下，势垒消失，核壳 NP 相对于壳材料的体沉积变得不稳定。通过使用现实的原子间势进行计算机模拟，对模型进行了简要讨论，说明了其在特定系统中的应用。这些具体研究中最引人注目的结果之一是，取决于纳米粒子的大小，是否会出现亚稳的核壳。
