论文标题
纳米簇水溶液控制密集聚合物膜的离子分区
Aqueous Nanoclusters Govern Ion Partitioning in Dense Polymer Membranes
论文作者
论文摘要
水溶液中反应性聚合物膜和水凝胶对带电分子的吸收和吸附是对软功能材料的发展至关重要的。在这里，我们调查了简单单子素（Na $^+$，K $^+$，CS $^+$，Cl $^ - $，I $^ - $）和一种分子离子（4-硝基苯甲酸酯； NP $^ - $）的分区，并在密集的，电源的poly（$ n $ iSopropypopylapylacylacylacy lambrane）中使用expolantials exploine smorciits expolantial sunication。在多分散水纳米簇网络中，主要是疏水环境内部的水。平均簇大小决定了简单离子的平均静电自我能源，最好驻留在它们内部。因此，我们发现比使用统一的介电常数从简单出生的图片中预期的$ k \ simeq \> $ 10 $^{ - 1} $要大得多。尽管它们的形状不规则，但我们观察到水簇在周围的环境中具有通用的负静电潜力，这是水性液体蒸气界面所知的。我们发现，在对称单子盐的情况下，我们发现这种潜力可以显着影响较大带电分子的自由能，因为它们的水合弱和对接口的亲和力增加。 Consequently, and in stark contrast to the simple ions, the molecular ion NP$^-$ can have a partition ratio much larger than unity, $K\simeq\>$10-30 (depending on the cation type) or even $10^3$ in excess of monovalent salt, which explains recent observations of enhanced reaction kinetics of NP$^-$ reduction catalyzed within dense polymer networks.这些结果还表明，电离分子甚至可以增强崩溃的，相当疏水的凝胶中的分配，从而强烈挑战传统的简单推理。
The uptake and sorption of charged molecules by responsive polymer membranes and hydrogels in aqueous solutions is of key importance for the development of soft functional materials. Here we investigate the partitioning of simple monoatomic (Na$^+$, K$^+$, Cs$^+$, Cl$^-$, I$^-$) and one molecular ion (4-nitrophenolate; NP$^-$) within a dense, electroneutral poly($N$-isopropylacrylamide) membrane using explicit-water molecular dynamics simulations. Inside the predominantly hydrophobic environment water distributes in a network of polydisperse water nanoclusters. The average cluster size determines the mean electrostatic self-energy of the simple ions, which preferably reside deeply inside them; we therefore find substantially larger partition ratios $K\simeq\>$10$^{-1}$ than expected from a simple Born picture using a uniform dielectric constant. Despite their irregular shapes we observe that the water clusters possess a universal negative electrostatic potential with respect to their surrounding, as is known for aqueous liquid-vapor interfaces. This potential, which we find concealed in cases of symmetric monoatomic salts, can dramatically impact the transfer free energies of larger charged molecules because of their weak hydration and increased affinity to interfaces. Consequently, and in stark contrast to the simple ions, the molecular ion NP$^-$ can have a partition ratio much larger than unity, $K\simeq\>$10-30 (depending on the cation type) or even $10^3$ in excess of monovalent salt, which explains recent observations of enhanced reaction kinetics of NP$^-$ reduction catalyzed within dense polymer networks. These results also suggest that ionizing a molecule can even enhance the partitioning in a collapsed, rather hydrophobic gel, which strongly challenges the traditional simplistic reasoning.
