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Abstract：
The addition of molecular liquid cosolvents to choline chloride (ChCl)-based deep eutectic solvents (DESs) is increasingly investigated for reducing the inherently high bulk viscosities of the latter, which represent a major obstacle for potential industrial applications. The molar enthalpy of mixing, often referred to as excess molar enthalpy H E-a property reflecting changes in intermolecular interactions upon mixing-of the well-known ChCl/ethylene glycol (1:2 molar ratio) DES mixed with either water or methanol was recently found to be of opposite sign at 308.15 K: Mixing of the DES with water is strongly exothermic, while methanol mixtures are endothermic over the entire mixture composition range. Knowledge of molecular-level liquid structural changes in the DES following cosolvent addition is expected to be important when selecting such \"pseudo-binary\" mixtures for specific applications, e.g., solvents. With the aim of understanding the reason for the different behavior of selected DES/water or methanol mixtures, we performed classical MD computer simulations to study the changes in intermolecular interactions thought to be responsible for the observed H E sign difference. Excess molar enthalpies computed from our simulations reproduce, for the first time, the experimental sign difference and composition dependence of the property. We performed a structural analysis of simulation configurations, revealing an intriguing difference in the interaction modes of the two cosolvents with the DES chloride anion: water molecules insert between neighboring chloride anions, forming ionic hydrogen-bonded bridges that draw the anions closer, whereas dilution of the DES with methanol results in increased interionic separation. Moreover, the simulated DES/water mixtures were found to contain extended hydrogen-bonded structures containing water-bridged chloride pair arrangements, the presence of which may have important implications for solvent applications.
摘要：
越来越多地研究将分子液体共溶剂添加到氯化胆碱（ChCl）基深共晶溶剂（DES）中，以降低后者固有的高体积粘度。这是潜在工业应用的主要障碍。混合的摩尔焓，通常被称为过量摩尔焓HE-反映分子间相互作用变化的性质-最近发现与水或甲醇混合的众所周知的ChCl/乙二醇（1：2摩尔比）DES在308.15K时具有相反的符号：DES与水的混合强烈放热，而甲醇混合物在整个混合物组成范围内是吸热的。在选择用于特定应用的“伪二元”混合物时，对助溶剂添加后DES中分子水平的液态结构变化的了解是很重要的。例如，溶剂。为了了解所选DES/水或甲醇混合物行为不同的原因，我们进行了经典的MD计算机模拟，以研究被认为是观察到的HE符号差异的分子间相互作用的变化。从我们的模拟计算出的过量摩尔焓再现，第一次,性质的实验符号差异和成分依赖性。我们对仿真配置进行了结构分析，揭示了两种共溶剂与DES氯化物阴离子的相互作用模式的有趣差异：水分子插入相邻的氯化物阴离子之间，形成离子氢键桥，拉近阴离子，而用甲醇稀释DES会导致离子间分离增加。此外，模拟的DES/水混合物被发现含有扩展的氢键结构，含有水桥氯化物对排列，其存在可能对溶剂应用具有重要意义。
