Abstract Recently, mixtures of ionic liquids (ILs) containing acetate [oAc−] and tricyanomethanide [C(CN)3−] anions have demonstrated promising characteristics as solvents and as CO2 adsorbents. The anion composition can be optimized to obtain a significant improvement in the diffusivity while only slightly decreasing the solubility. Here, we explore a similar investigation applied to an ionic polyimide (i-PI) material in order to understand the molecular-level kinetic and thermodynamic characteristics that emerge when a polymeric material is used instead. The i-PI systems studied are part of an emerging class of “high-performance” ionene polymers that hold significant potential for applications in gas separation membranes. Here, neat i-PI systems with the two counter anions, [oAc−] and [C(CN)3−], at varying concentrations are modeled by a combination of molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. Higher concentrations of [C(CN)3−] are predicted to improve CO2 diffusion, similar to the pure IL performance, while solubility remains relatively unchanged. The structural characteristics of the i-PI systems provide detailed insight into the effect that the anions have on the adsorption properties. The solubility is weakly related to the theoretical surface area, and the diffusivity is moderately correlated to the fractional free volume (FFV). Overall, the combination of different anions is predicted to be a viable strategy for improving the diffusivity throughout i-PI materials, but the behavior of pure ILs cannot be simply extrapolated to ion behavior in membranes.

中文翻译：

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CO2 在具有 [C(CN)3]x[oAc]1-x 阴离子组成的离子聚酰亚胺中的溶解度和扩散性

摘要 最近，含有醋酸盐 [oAc-] 和三氰基甲烷 [C(CN)3-] 阴离子的离子液体 (IL) 的混合物已显示出作为溶剂和 CO2 吸附剂的良好特性。可以优化阴离子组成以获得扩散率的显着改善，同时仅略微降低溶解度。在这里，我们探索了一项应用于离子聚酰亚胺 (i-PI) 材料的类似研究，以了解使用聚合物材料时出现的分子级动力学和热力学特性。所研究的 i-PI 系统是一类新兴的“高性能”紫罗烯聚合物的一部分，在气体分离膜中具有巨大的应用潜力。在这里，具有两个抗衡阴离子 [oAc−] 和 [C(CN)3−] 的整洁 i-PI 系统，通过分子动力学 (MD) 和大经典蒙特卡罗 (GCMC) 模拟的组合对不同浓度的 预计更高浓度的 [C(CN)3-] 会改善 CO2 扩散，类似于纯 IL 性能，而溶解度保持相对不变。i-PI 系统的结构特征提供了对阴离子对吸附性能影响的详细了解。溶解度与理论表面积微弱相关，而扩散率与分数自由体积 (FFV) 适度相关。总体而言，预计不同阴离子的组合是提高 i-PI 材料扩散率的可行策略，但不能简单地将纯离子液体的行为外推到膜中的离子行为。