Nanoscale structure of protic ionic liquids is critical to their utility as molecular electrochemical solvents since it determines the capacity to dissolve salts and polymers such as poly(ethylene oxide) (PEO). Here we use quantum chemical molecular dynamics simulations to investigate the impact of dissolved halide anions on the nanostructure of an archetypal nanostructured protic ionic liquid, propylammonium nitrate (PAN), and how this impacts the solvation of a model PEO polymer. At the molecular level, PAN is nanostructured, consisting of charged/polar and uncharged/nonpolar domains. The charged domain consists of the cation/anion charge groups, and is formed by their electrostatic interaction. This domain solvophobically excludes the propyl chains on the cation, which form a distinct, self-assembled nonpolar domain within the liquid. Our simulations demonstrate that the addition of Cl⁻ and Br⁻ anions to PAN disrupts the structure within the PAN charged domain due to competition between nitrate and halide anions for the ammonium charge centre. This disruption increases with halide concentration (up to 10 mol. %). However, at these concentrations, halide addition has little effect on the structure of the PAN nonpolar domain. Addition of PEO to pure PAN also disrupts the structure within the charged domain of the liquid due to hydrogen bonding between the charge groups and the terminal PEO hydroxyl groups. There is little other association between the PEO structure and the surrounding ionic liquid solvent, with strong PEO self-interaction yielding a compact, coiled polymer morphology. Halide addition results in greater association between the ionic liquid charge centres and the ethylene oxide components of the PEO structure, resulting in reduced conformational flexibility, compared to that observed in pure PAN. Similarly, PEO self-interactions increase in the presence of Cl⁻ and Br⁻ anions, compared to PAN, indicating that the addition of halide salts to PAN decreases its utility as a molecular solvent for polymers such as PEO.

中文翻译：

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聚环氧乙烷和卤化物盐存在下硝酸丙基铵的纳米结构

质子性离子液体的纳米级结构对其作为分子电化学溶剂的用途至关重要，因为它决定了溶解盐和聚合物（例如聚环氧乙烷（PEO））的能力。在这里，我们使用量子化学分子动力学模拟来研究溶解的卤化物阴离子对原型纳米结构质子离子液体硝酸丙基铵（PAN）的纳米结构的影响，以及这如何影响模型PEO聚合物的溶剂化。在分子水平上，PAN是纳米结构，由带电/极性和不带电/非极性域组成。带电域由阳离子/阴离子电荷基团组成，并由它们的静电相互作用形成。该结构域疏水性地排除了阳离子上的丙基链，这些丙基链在液体中形成了一个独特的，自组装的非极性结构域。^-和Br ^-由于硝酸根和卤化物阴离子争夺铵电荷中心，PAN的阴离子破坏了PAN带电域内的结构。这种破坏随着卤化物浓度（至多10 mol。％）而增加。但是，在这些浓度下，添加卤化物对PAN非极性域的结构影响很小。由于电荷基团和末端PEO羟基之间的氢键，将PEO添加至纯PAN也破坏了液体带电域内的结构。PEO结构与周围的离子液体溶剂之间几乎没有其他关联，而强大的PEO自相互作用产生了紧凑的，盘绕的聚合物形态。卤化物的添加导致离子液体电荷中心与PEO结构的环氧乙烷组分之间的缔合程度更高，与纯PAN中观察到的相比，导致构象柔韧性降低。同样，在氯的存在下，PEO的自相互作用增加^-和Br ^-阴离子，相对于PAN，表明加成卤化物盐以PAN降低其作为用于聚合物如PEO的分子量溶剂效用。