Center for Molecular Modeling, DCB∕CIT, NIH, U.S. DHHS, Bethesda, Maryland 20892, USA.
J Chem Phys. 2011 Mar 21;134(11):114508. doi: 10.1063/1.3560637.
Solute-cluster aggregation and particle fusion have recently been suggested as alternative routes to the classical mechanism of nucleation from solution. The role of both processes in the crystallization of an aqueous electrolyte under controlled salt addition is here elucidated by molecular dynamics simulation. The time scale of the simulation allows direct observation of the entire crystallization pathway, from early events in the prenucleation stage to the formation of a nanocrystal in equilibrium with concentrated solution. The precursor originates in a small amorphous aggregate stabilized by hydration forces. The core of the nucleus becomes crystalline over time and grows by coalescence of the amorphous phase deposited at the surface. Imperfections of ion packing during coalescence promote growth of two conjoint crystallites. A parameter of order and calculated cohesive energies reflect the increasing crystalline order and stress relief at the grain boundary. Cluster aggregation plays a major role both in the formation of the nucleus and in the early stages of postnucleation growth. The mechanism identified shares common features with nucleation of solids from the melt and of liquid droplets from the vapor.
最近有人提出，溶质-团簇聚集和颗粒融合是除经典溶液成核机制以外的另外两种成核途径。本文通过分子动力学模拟阐明了这两个过程在受控盐添加下的水溶液电解质结晶中的作用。模拟的时间尺度允许直接观察整个成核途径，从成核前阶段的早期事件到与浓溶液达到平衡的纳米晶体的形成。前体起源于由水合力稳定的小无定形聚集体。随着时间的推移，核的核心逐渐结晶，并通过在表面沉积的无定形相的聚结而生长。在聚结过程中离子排列的不完美会促进两个共格晶体的生长。有序参数和计算的内聚能反映了晶粒边界处结晶度的增加和应力释放。团簇聚集在核的形成和成核后生长的早期阶段都起着重要作用。所确定的机制与从熔体中生成固体以及从蒸汽中生成液滴的成核具有共同特征。
