Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
J Phys Chem B. 2022 Jul 21;126(28):5274-5290. doi: 10.1021/acs.jpcb.2c01764. Epub 2022 Jul 6.
The crystal growth of urea was analyzed with all-atom molecular dynamics (MD) simulation for the (001) and (110) faces in contact with aqueous solutions. The local environment of a crystallizing molecule was treated in terms of the numbers of crystalline neighbors and the orientation relative to the crystal surface, and the molecular-level inhomogeneity of a growing surface was addressed by decomposing the overall rate of growth into a sum of the contributions conditioned by the local structure and orientation mode. The contrast of the growth mechanism between the (001) and (110) faces was then evidenced by the local contributions, and the roles of the outer layers of the crystal toward the liquid region were pointed out for (001). The effect of the additive species in the liquid on the crystal growth of urea was investigated with biuret, ,-dimethylformamide (DMF), and acetone. The growth was observed to be suppressed more strongly in the order of biuret > DMF > acetone, and it was found that the ordering of suppression by the additive is common irrespective of the local environment of a crystallizing urea. This finding implies that the additive's effect on the crystal growth can be predicted by treating the flat surface, which is a convenient system for detailed analyses at atomic resolution. The correspondence to the free energy of adsorption of the additive was then examined for the additive-induced modulation of the growth rate. It was seen that the adsorption free energy correlates to the extent of modulation of the growth rate, and the interaction components that govern the adsorption propensity were identified.
采用全原子分子动力学 (MD) 模拟方法，研究了在水溶液中与（001）和（110）晶面接触时尿素的晶体生长。根据结晶分子相对于晶面的位置和晶面邻居的数量，对结晶分子的局部环境进行了处理，通过将总生长速率分解为局部结构和取向模式条件下的贡献之和，解决了生长表面的分子水平不均匀性问题。通过局部贡献，证明了（001）和（110）晶面之间生长机制的差异，并指出了晶体外层对（001）向液相区域的作用。通过缩二脲、-二甲基甲酰胺 (DMF) 和丙酮研究了添加剂物种对尿素晶体生长的影响。观察到生长抑制的强度顺序为缩二脲 > DMF > 丙酮，并且发现添加剂对生长的抑制顺序与结晶尿素的局部环境无关，这是普遍存在的。这一发现意味着可以通过处理平面表面来预测添加剂对晶体生长的影响，平面表面是进行原子分辨率详细分析的便利系统。然后检查了添加剂诱导的生长速率调制与吸附自由能的对应关系。结果表明，吸附自由能与生长速率调制的程度相关，并且确定了控制吸附倾向的相互作用分量。
