Instituto de Química Física Rocasolano, Consejo Superior de Investigaciones Científicas, CSIC, Calle Serrano 119, 28006 Madrid, Spain.
Center for Soft Matter Research, Department of Physics, New York University, New York, New York 10003, USA.
J Chem Phys. 2019 Sep 7;151(9):094502. doi: 10.1063/1.5109382.
Here, we revisit the assembly of colloidal tetrahedral patchy particles. Previous studies have shown that the crystallization of diamond from the fluid phase depends more critically on patch width than on the interaction range: particles with patches narrower than 40° crystallize readily and those with wide patches form disordered glass states. We find that the crystalline structure formed from the fluid also depends on the patch width. Whereas particles with intermediate patches assemble into diamond (random stacking of cubic and hexagonal diamond layers), particles with narrow patches (with width ≈20° or less) crystallize frequently into clathrates. Free energy calculations show that clathrates are never (in the pressure-temperature plane) thermodynamically more stable than diamond. The assembly of clathrate structures is thus attributed to kinetic factors that originate from the thermodynamic stabilization of pentagonal rings with respect to hexagonal ones as patches become more directional. These pentagonal rings present in the fluid phase assemble into sII clathrate or into large clusters containing 100 particles and exhibiting icosahedral symmetry. These clusters then grow by interpenetration. Still, the organization of these clusters into extended ordered structures was never observed in the simulations.
在这里，我们重新审视胶体四面体补丁颗粒的组装。先前的研究表明，从流体相结晶金刚石更关键地取决于补丁宽度而不是相互作用范围：宽度小于 40°的补丁颗粒很容易结晶，而宽补丁颗粒形成无序的玻璃态。我们发现，从流体中形成的晶体结构也取决于补丁的宽度。具有中等补丁的颗粒组装成金刚石（立方和六方金刚石层的随机堆积），而具有较窄补丁（宽度约为 20°或更小）的颗粒则经常结晶成笼形物。自由能计算表明，笼形物在压力-温度平面上从未（热力学上）比金刚石更稳定。笼形结构的组装归因于动力学因素，这些因素源于随着补丁变得更具方向性，五边形环相对于六边形环在热力学上的稳定化。这些存在于流体相中的五边形环组装成 sII 笼形物或含有 100 个颗粒且表现出二十面体对称性的大簇。然后这些簇通过相互渗透生长。尽管如此，在模拟中从未观察到这些簇形成扩展有序结构。
