Department of Chemistry, Stanford University , Stanford, California 94305, United States.
J Am Chem Soc. 2017 Jan 11;139(1):311-323. doi: 10.1021/jacs.6b10695. Epub 2016 Dec 27.
Supported ionic liquid membranes (SILMs) are membranes that have ionic liquids impregnated in their pores. SILMs have been proposed for advanced carbon capture materials. Two-dimensional infrared (2D IR) and polarization selective IR pump-probe (PSPP) techniques were used to investigate the dynamics of reorientation and spectral diffusion of the linear triatomic anion, SeCN, in poly(ether sulfone) (PES) membranes and room-temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimNTf). The dynamics in the bulk EmimNTf were compared to its dynamics in the SILM samples. Two PES membranes, PES200 and PES30, have pores with average sizes, ∼300 nm and ∼100 nm, respectively. Despite the relatively large pore sizes, the measurements reveal that the reorientation of SeCN and the RTIL structural fluctuations are substantially slower in the SILMs than in the bulk liquid. The complete orientational randomization, slows from 136 ps in the bulk to 513 ps in the PES30. 2D IR measurements yield three time scales for structural spectral diffusion (SSD), that is, the time evolution of the liquid structure. The slowest decay constant increases from 140 ps in the bulk to 504 ps in the PES200 and increases further to 1660 ps in the PES30. The results suggest that changes at the interface propagate out and influence the RTIL structural dynamics even more than a hundred nanometers from the polymer surface. The differences between the IL dynamics in the bulk and in the membranes suggest that studies of bulk RTIL properties may be poor guides to their use in SILMs in carbon capture applications.
支持离子液体膜（SILM）是指在其孔中浸渍有离子液体的膜。SILM 已被提议用于先进的碳捕集材料。二维红外（2D IR）和偏振选择红外泵浦探针（PSPP）技术被用于研究线性三原子阴离子 SeCN 在聚醚砜（PES）膜和室温离子液体（RTIL）1-乙基-3-甲基咪唑双（三氟甲基磺酰基）亚胺（EmimNTf）中的重定向和光谱扩散动力学。将 bulk EmimNTf 的动力学与 SILM 样品中的动力学进行了比较。两种 PES 膜，PES200 和 PES30，具有平均孔径分别约为 300nm 和 100nm。尽管孔径相对较大，但测量结果表明，在 SILM 中，SeCN 的重定向和 RTIL 结构波动比在 bulk 液体中慢得多。从 bulk 的 136ps 完全定向随机化减慢到 PES30 的 513ps。2D IR 测量得到了结构光谱扩散（SSD）的三个时间尺度，即液体结构的时间演化。最慢的衰减常数从 bulk 的 140ps 增加到 PES200 的 504ps，并进一步增加到 PES30 的 1660ps。结果表明，界面处的变化会传播出去，并影响 RTIL 的结构动力学，即使距离聚合物表面超过一百纳米。IL 在 bulk 和膜中的动力学之间的差异表明，对 bulk RTIL 性质的研究可能不能很好地指导其在碳捕集应用中的 SILM 中使用。
