Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara 93106-9010, United States.
Department of Materials, ETH Zürich, Zürich 8093, Switzerland.
J Phys Chem B. 2021 May 27;125(20):5408-5419. doi: 10.1021/acs.jpcb.1c01460. Epub 2021 May 12.
Polymeric ionogels, cross-linked gels swollen by ionic liquids (ILs), are useful vehicles for the release and storage of molecular solutes in separation, delivery, and other applications. Although rapid solute diffusion is often critical for performance, it remains challenging to predict diffusivities across multidimensional composition spaces. Recently, we showed that water (a neutral solute) diffuses through alkyl-methylimidazolium halide ILs by hopping between hydrogen bonding sites on relatively immobile cations. Here, we expand on this activated hopping mechanism in two significant ways. First, we demonstrate that water diffuses through poly(ethylene glycol)diacrylate ionogels via the same mechanism at a reduced rate. Second, we hypothesize that the activation energy barrier can be determined from relatively simple H NMR chemical shift measurements of the proton responsible for H-bonding. This relationship enables water's diffusivity in ionogels of this class to be predicted quantitatively, requiring only (1) the composition-dependent diffusivity and Arrhenius behavior of a single IL and (2) H NMR spectra of the ionogels of interest. High-throughput microfluidic Fabry-Perot interferometry measurements verify prediction accuracy across a broad formulation space (four ILs, 0 ≤ ≤ 0.7, 0 ≤ ϕ ≤ 0.66). The predictive model may expedite IL-material screening; moreover, it intimates a powerful connection between solute mobility and hydrogen bonding and suggests targets for rational design.
聚合物离子凝胶是由离子液体（ILs）溶胀的交联凝胶，是分离、输送和其他应用中分子溶质释放和储存的有用载体。尽管快速的溶质扩散通常对性能至关重要，但要预测多维组成空间中的扩散率仍然具有挑战性。最近，我们表明，水（一种中性溶质）通过相对不移动的阳离子上氢键结合位点之间的跳跃扩散通过烷基甲基咪唑卤化物 IL。在这里，我们以两种重要方式扩展了这种激活跳跃机制。首先，我们证明水通过聚（乙二醇）二丙烯酸酯离子凝胶以相同的机制扩散，但速率降低。其次，我们假设可以通过负责氢键的质子的相对简单的 H NMR 化学位移测量来确定活化能垒。这种关系使该类离子凝胶中水的扩散系数能够定量预测，仅需要 (1) 单个 IL 的组成依赖性扩散系数和 Arrhenius 行为，以及 (2) 感兴趣的离子凝胶的 H NMR 光谱。高通量微流控 Fabry-Perot 干涉测量技术在广泛的配方空间（四种 IL，0 ≤ ≤ 0.7，0 ≤ ϕ ≤ 0.66）中验证了预测的准确性。预测模型可以加快 IL 材料的筛选；此外，它暗示了溶质迁移率与氢键之间的强大联系，并为合理设计提供了目标。
