Spinodal for the solution-to-crystal phase transformation
Spinodal for the solution-to-crystal phase transformation
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DOI：
10.1063/1.1943413
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发表时间：
2005-07-01
影响因子：
4.4
通讯作者：
Vekilov, PG
中科院分区：
文献类型：
--
作者：
Filobelo, LF;Galkin, O;Vekilov, PG
在许多体系中，溶液中晶核的形成分两步进行：无序中间体的准小滴的形成，然后在这些小滴中有序结晶胚的成核。每一步的速率取决于各自的自由能势垒及其近临界团簇的增长率。我们通过实验讨论了自由能势垒和动力学因素对溶液中晶体成核的相对意义。我们发现晶体的成核比致密液滴的成核慢8-10个数量级，即第二步是速率决定。我们发现，在3或4 k(B)T单位的过饱和下，5个、4个或3个分子的晶核转变为单分子核，即显著的成核势垒在分子的热能以下消失。我们发现决定晶体成核速率的主要因素是在无序中间体的准小团簇中近临界有序团簇的缓慢生长。与过饱和流体中的spinodal类似，我们定义了从溶液到晶体的spinodal，从过渡到单分子结晶核。我们发现，非均相成核中心加速成核不仅是因为经典理论所设想的降低成核屏障的润湿效应，而且还有助于有序结晶胚胎的生长动力学。(c) 2005年美国物理研究所。
The formation of crystalline nuclei from solution has been shown for many systems to occur in two steps: the formation of quasidroplets of a disordered intermediate, followed by the nucleation of ordered crystalline embryos within these droplets. The rate of each step depends on a respective free-energy barrier and on the growth rate of its near-critical clusters. We address experimentally the relative significance of the free-energy barriers and the kinetic factors for the nucleation of crystals from solution using a model protein system. We show that crystal nucleation is 8-10 orders of magnitude slower than the nucleation of dense liquid droplets, i.e., the second step is rate determining. We show that at supersaturations of three or four k(B)T units, crystal nuclei of five, four, or three molecules transform into single-molecule nuclei, i.e., the significant nucleation barrier vanishes below the thermal energy of the molecules. We show that the main factor, which determines the rate of crystal nucleation, is the slow growth of the near-critical ordered clusters within the quasidroplets of the disordered intermediate. Analogous to the spinodal in supersaturated fluids, we define a solution-to-crystal spinodal from the transition to single-molecule crystalline nuclei. We show that heterogeneous nucleation centers accelerate nucleation not only because of the wettinglike effects that lower the nucleation barrier, as envisioned by classical theory, but by helping the kinetics of growth of the ordered crystalline embryos. (c) 2005 American Institute of Physics.