Qi Weikai, Peng Yi, Han Yilong, Bowles Richard K, Dijkstra Marjolein
Soft Condensed Matter, Debye Institute for Nanomaterials Science, Department of Physics, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands.
Department of Chemistry, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5C9, Canada.
Phys Rev Lett. 2015 Oct 30;115(18):185701. doi: 10.1103/PhysRevLett.115.185701. Epub 2015 Oct 29.
A solid-solid phase transition of colloidal hard spheres confined between two planar hard walls is studied using a combination of molecular dynamics and Monte Carlo simulation. The transition from a solid consisting of five crystalline layers with square symmetry (5□) to a solid consisting of four layers with triangular symmetry (4△) is shown to occur through a nonclassical nucleation mechanism that involves the initial formation of a precritical liquid cluster, within which the cluster of the stable 4△ phase grows. Free-energy calculations show that the transition occurs in one step, crossing a single free-energy barrier, and that the critical nucleus consists of a small 4△ solid cluster wetted by a metastable liquid. In addition, the liquid cluster and the solid cluster are shown to grow at the planar hard walls. We also find that the critical nucleus size increases with supersaturation, which is at odds with classical nucleation theory. The △-solid-like cluster is shown to contain both face-centered-cubic and hexagonal-close-packed ordered particles.
运用分子动力学和蒙特卡罗模拟相结合的方法，研究了限制在两个平面硬壁之间的胶体硬球的固-固相变。结果表明，从具有方形对称性的五层晶体（5□）组成的固体到具有三角形对称性的四层（4△）组成的固体的转变，是通过一种非经典成核机制发生的，该机制涉及预临界液体团簇的初始形成，稳定的4△相团簇在其中生长。自由能计算表明，转变一步发生，跨越单个自由能势垒，并且临界核由被亚稳液体润湿的小4△固体团簇组成。此外，液体团簇和固体团簇在平面硬壁上生长。我们还发现临界核尺寸随过饱和度增加，这与经典成核理论不一致。△类固体团簇显示包含面心立方和六方密排有序粒子。
