Generating Nonnative Structures in Binary Ionic Liquid Mixtures for Tunable Phase Equilibria Properties

离子液体是完全由离子组成的物质，可以通过结合多种阳离子和阴离子而设计成液体形式存在。由于它们基本不挥发的性质和独特的物理化学性质，它们已成为潜在的环境友好化学品。通过明智地选择离子上的阳离子、阴离子或官能团，可以赋予离子液体所需的物理、化学和生物特性，使其成为真正的设计型溶剂。虽然这种组合方法可能被用来生产多达100万种离子液体，但离子液体领域的一个持续挑战是，许多离子液体表现出不利的传输性能，限制了它们在工业过程中的使用。此外，在气体分离等工业应用中，具有传输性质的离子液体通常含有氟离子，由于其毒性和较差的生物降解性，增加了其生产成本和环境问题。具有不同组成的离子液体的二元混合物可能提供对分子相互作用的精确微调，以产生所需的性质。根据一项估计，存在10亿个二元离子液体组合；因此，非常希望先验地预测二元离子液体混合物的性质。然而，目前还缺乏关于可应用于得出这一结论的设计规则的基本知识。这项研究旨在填补这一关键的知识缺口。提出的建议是基于这样的假设，即当两种氢键能力差异很大的离子液体结合在一起时，就会出现非天然分子相互作用方面的非理想性；非理想行为反映在气体溶解度对二元混合物组成的非线性依赖上。该假说的有效性将通过(I)确定由氢键能力差异很大的离子液体组成的二元混合物建立新的相互作用的程度，以及(Ii)评估这种相互作用对二元离子液体与二氧化碳和甲烷等气体混合物的相平衡性质的影响。分子动力学模拟将被用来阐明由两种离子液体组成的混合物中存在的分子水平相互作用，而自由能计算和蒙特卡罗方法将被用来计算这些混合物中物质的相平衡。拟议的研究和教育的整合旨在创造一个激发智力的环境，培训研究生和本科生理解分子现象在设计高效化学系统中的作用。拟议的外展计划针对STEM领域来自不同背景和代表性不足的人群。

Ionic liquids are substances that are composed entirely of ions and can be designed to exist as liquids by combining a wide range of cations and anions. They have emerged as potentially environmentally benign chemicals due to their essentially nonvolatile nature and unique physicochemical properties. By judiciously selecting the cation, anion or functional groups on the ions, desired physical, chemical and biological properties can be imparted to ionic liquids making them truly designer solvents. Although such a combinatorial approach can potentially be exploited to generate as many as one million ionic liquids, a continuing challenge in the field of ionic liquids is that many ionic liquids display unfavorable transport properties limiting their use in industrial processes. Further, ionic liquids with transport properties in the range of interest for industrial applications, such as gas separations, usually contain fluorinated ions raising their production cost and environmental concern due to toxicity and poor biodegradability. Binary mixtures of ionic liquids with different compositions can potentially provide precise fine-tuning of the molecular interactions to generate desired properties. According to one estimate, there are one billion binary ionic liquid combinations; thus, it is highly desirable to predict a priori the properties of binary ionic liquid mixtures. However, at present, there is a lack of fundamental knowledge regarding the design rules that can be applied to arrive at such a conclusion. The proposed research is geared toward fulfilling this critical knowledge gap.The proposal is guided by the hypothesis that nonideality in the binary ionic liquid mixtures in terms of non-native molecular interactions occurs when two ionic liquids differing widely in their hydrogen bonding ability are combined; the nonideal behavior is reflected in the nonlinear dependence of solubility of gases on the composition of the binary mixture. The validity of the hypothesis will be tested by (i) determining the extent to which novel interactions are established for binary mixtures composed of ionic liquids differing widely in their hydrogen bonding ability and (ii) evaluating the effect of such interactions on the phase equilibria properties of binary ionic liquids mixtures with gases, such as carbon dioxide and methane. Molecular dynamics simulations will be carried out to elucidate molecular level interactions present in the mixtures composed of two ionic liquids while free-energy calculations and Monte Carlo methods will be employed for calculation of phase equilibria of substances in these mixtures. The proposed integration of research and education aims at creating an intellectually stimulating environment for training graduate and undergraduate students on understanding the role of molecular phenomena in designing efficient chemical systems. The proposed outreach plan is targeting students from diverse backgrounds and underrepresented populations in STEM fields.