竞争能量学调控固有微孔聚合物（PIM）膜中的气体渗透
Competing Energetics Govern Gas Permeation in Polymer of Intrinsic Microporosity (PIM) Membranes
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中文总结 AI 辅助
本研究采用非平衡分子动力学模拟，揭示PIM膜中气体渗透由气体-壁相互作用势能与热动能的竞争调控，明确了两种entry路径及温度对传输机制的影响，为微孔聚合物膜气体传输研究提供了孔流视角。
中文摘要 AI 辅助
聚合物膜，尤其是固有微孔聚合物（PIMs），在气体分离应用中具有巨大潜力。然而，长期主导的溶解-扩散模型将膜视为无孔均匀介质，无法解释气体-固体原子相互作用如何调控固有微孔中的分子传输，限制了从底层出发的合理膜设计。本研究采用非平衡分子动力学模拟，探究多种气体（He、H₂、CH₄、N₂、O₂和CO₂）在不同温度下通过代表性PIM膜PIM-1的渗透行为。通过分析气体渗透率随分子质量的标度关系，我们发现主导传输机制存在温度诱导的转变，该转变由气体-壁相互作用势能与热动能的竞争决定：弱相互作用或高温有利于努森型弹道传输，而强相互作用及低温则有利于吸附介导的表面扩散。此外，对膜界面处的分子轨迹分析揭示了两种不同的 entry 路径：直接通过孔开口 entry 和表面扩散辅助 entry。表面扩散辅助路径极大促进了强相互作用气体 entry 进入膜内，提升了整体渗透率，但该增强效应随温度升高而减弱。这些发现为PIM-1中的气体渗透提供了机制性图景，解释了气体渗透对气体类型和温度的依赖性，更广泛而言，强调了采用孔流视角理解微孔聚合物膜中气体传输的重要性。
英文摘要
Polymer membranes, particularly polymers of intrinsic microporosity (PIMs), hold great promise for gas separation applications. However, the long-dominant solution-diffusion model, which treats the membrane as a nonporous homogeneous medium, does not resolve how gas-solid atomic interactions govern molecular transport in intrinsic micropores, limiting rational bottom-up membrane design. In this work, we employ non-equilibrium molecular dynamics simulations to investigate the permeation of various gases (He, H2, CH4, N2, O2, and CO2) through PIM-1 as a representative PIM membrane across a range of temperatures. By analyzing the scaling of gas permeability with molecular mass, we identify a temperature-induced transition in the dominant transport mechanism. We demonstrate that this transition is governed by the competition between gas-wall interaction potential energy and thermal kinetic energy: weak interactions or elevated temperatures facilitate Knudsen-type ballistic transport, whereas strong interactions and lower temperatures favor adsorption-mediated surface diffusion. Furthermore, molecular trajectory analysis at the membrane interface reveals two distinct entry pathways: direct entry through pore openings and surface-diffusion-assisted entry. The surface-diffusion-assisted pathway greatly promotes the entry of strongly interacting gases into the membrane, contributing to higher overall permeability, albeit this enhancement diminishes with increasing temperature. These findings offer a mechanistic picture of gas permeation in PIM-1 and explain the dependence of gas permeation on both gas type and temperature. More broadly, they highlight the importance of adopting a pore-flow perspective to understand gas transport in microporous polymer membranes.
