Department of Chemical Engineering, Indian Institute of Science, Bangalore, India.
J Chem Phys. 2017 Aug 14;147(6):064504. doi: 10.1063/1.4997432.
Co-crystal formation from fluid-mixtures is quite common in a large number of systems. The simplest systems that show co-crystal (also called substitutionally ordered solids) formation are binary hard sphere mixtures. In this work, we study the nucleation of AB type solid compounds using Monte Carlo molecular simulations in binary hard sphere mixtures with the size ratio of 0.55. The conditions chosen for the study lie in the region where nucleation of an AB type solid competes with that of a pure A solid with a face-centered-cubic structure. The fluid phase composition is kept equal to that of the AB type solid. The nucleation free-energy barriers are computed using the seeding technique of Sanz et al. [J. Am. Chem. Soc. 135, 15008 (2013)]. Our simulation results show that the nucleation of the AB type solid is favored even under conditions where the pure A solid is more stable. This is primarily due to the similarity in the composition of the fluid phase and the AB type solid which in turn leads to much lower interfacial tension between the crystal nucleus and the fluid phase. This system is an example of how the fluid phase composition affects the structure of the nucleating solid phase during crystallization and has relevance to crystal polymorphism during crystallization processes.
共晶从流体混合物中形成在大量系统中非常常见。最简单的显示共晶（也称为取代有序固体）形成的系统是二元硬球混合物。在这项工作中，我们使用蒙特卡罗分子模拟研究了 AB 型固体化合物在尺寸比为 0.55 的二元硬球混合物中的成核。选择的研究条件位于 AB 型固体成核与具有面心立方结构的纯 A 固体成核竞争的区域。流体相组成保持与 AB 型固体相同。使用 Sanz 等人的种子技术计算成核自由能垒。[J. Am. Chem. Soc. 135, 15008 (2013)]。我们的模拟结果表明，即使在纯 A 固体更稳定的条件下，AB 型固体的成核也更有利。这主要是由于流体相和 AB 型固体的组成相似，这反过来又导致晶核和流体相之间的界面张力低得多。该系统是流体相组成如何影响成核固体相结构的一个例子，在结晶过程中的晶体多形性中具有相关性。
