Molecular Dynamics Simulations of Gas Selectivity in Amorphous Porous Molecular Solids

Some organic cage molecules have
structures with protected, internal
pore volume that cannot be in-filled, irrespective of the solid-state
packing mode: that is, they are intrinsically porous. Amorphous packings
can give higher pore volumes than crystalline packings for these materials,
but the precise nature of this additional porosity is hard to understand
for disordered solids that cannot be characterized by X-ray diffraction.
We describe here a computational methodology for generating structural
models of amorphous porous organic cages that are consistent with
experimental data. Molecular dynamics simulations rationalize the
observed gas selectivity in these amorphous solids and lead to insights
regarding self-diffusivities, gas diffusion trajectories, and gas
hopping mechanisms. These methods might be suitable for the de novo
design of new amorphous porous solids for specific applications, where
“rigid host” approximations are not applicable.

某些有机笼状分子具有内部孔隙体积得到保护的独特结构，此孔隙体积无法填充，无论固态堆积模式为何：换言之，它们本质上具有多孔性。对于此类材料，非晶态堆积相较于晶态堆积能够提供更高的孔隙体积，然而，对于无法通过X射线衍射进行表征的无序固体，这种额外孔隙的确切性质难以理解。本文描述了一种计算方法，旨在生成与实验数据一致的非晶态多孔有机笼状结构模型。分子动力学模拟解释了这些非晶态固体中观察到的气体选择性，并揭示了关于自扩散率、气体扩散轨迹和气体跳跃机制等方面的见解。这些方法可能适用于针对特定应用的新非晶态多孔固体的从头设计，其中“刚性主体”近似不适用。