A Molecular-Based Framework for Studying the Thermodynamic Properties of Ionic Liquids

mccabeionic液体（ILs）是一种完全由离子组成的液体，其熔点在室温或低于室温，这与高温熔盐不同。由于其挥发性可以忽略不计，与传统有机溶剂相比，可将大气污染的风险降至最低，并减少相关的健康问题，因此在使用替代溶剂和绿色溶剂方面处于领先地位。从催化和生物催化，到分离和光化学电池，il显示出广泛的应用前景。对ILs的兴趣源于其独特的物理性质，超出了常规分子溶剂的范围，并且可以包括（除了无挥发性或低挥发性之外）热稳定性，液体温度范围广，以及溶解各种有机和无机材料的能力，包括大分子。液态离子通常由一个大的有机阳离子和一个弱配位的无机或有机阴离子组成，这阻碍了包装并降低了熔点。阳离子和阴离子各自赋予IL不同的物理化学性质，可以被取代以获得所需的性质，如果需要，可以功能化以提供进一步的控制。虽然最初对il的兴趣主要集中在它们的溶剂性质上，但最近在设计广泛应用的新功能材料中使用其新颖、可调的物理和化学性质的潜力激发了对il的兴趣。因此，迄今为止在IL设计方面取得了很大进展；然而，大部分进展是通过对财产修改采取经验方法取得的。大量可能的阳离子-阴离子组合使得能够根据其成分合理预测IL性质变得至关重要。因此，基于对il内部结构和相互作用的物理理解，有必要开发一种精确的工具来设计特定于任务的il。我们工作的目标是通过发展基于分子的理论框架来研究il的热力学性质来解决这一重要需求。ILs中存在的相互作用的复杂性使得使用计算工具进行研究从根本上具有挑战性。总体目标是开发一个框架，用它来准确地模拟IL系统及其与其他分子物种的混合物，并能够预测它们的热力学性质。在这项工作中，我们将专注于建立一个基于分子的纯il模型，这将为未来il和分子溶质/溶剂混合物的建模工作以及特定任务il的预测设计奠定基础。所开发的方法将根据实验数据和从头计算进行优化，并将能够从化学成分中预测IL的性质，从而消除在确定给定离子组合的性质时的猜测工作，并最终确定它们与分子物种的混合行为。具体来说，该项目将创建一个理论工具来描述建立在SAFT框架上的ILs，用于模拟流体相行为。与文献中现有的各种基于工程的状态方程相比，SAFT提供了一种基于分子的方法，并且在将分子形状、大小和相互作用的影响捕获到解析状态方程中的能力方面是无与伦比的。为了用上述基于分子的模型描述IL的热力学性质，PI将为IL系统开发一个理论框架，该框架将积分方程理论（准确描述偶极和离子流体的结构）的解析解与SAFT-VR方法的分子框架相结合。该方法的核心将是由PI开发的异分段SAFT模型，12它与基于同质分段方法的SAFT模型形成对比。，模型链中的每个片段具有相同的大小和相互作用的能量（参数）。拟议研究的智力价值-拟议的工作将导致新的方法，将从量子化学计算和分子模拟中获得的特性映射到基于统计力学的模型和液态理论的新发展所需的参数上。这项工作将通过提供基于对IL结构和相互作用的深刻物理理解的预测性IL设计方法，为分子热力学的重大进步奠定基础。拟议研究的更广泛影响-拟议研究与pi教育活动的整合将确保范德比尔特大学的学生接触并参与分子建模和分子热力学的前沿。将通过范德比尔特大学的NSF TLSAMP4项目寻求少数族裔的参与，并通过pi参与工程学院RET网站项目寻求高中教师的参与。总体计划- AIM 1：纯il的基于分子的模型AIM 2：基于分子的il和分子溶剂/溶质混合物模型AIM 3：特定任务il的预测设计PI将这个修订的探索性项目的范围限制在目标1，纯il的基于分子的模型，因为它代表了工作中最具挑战性和最新颖的部分。工作将集中在(1)推导和应用液态理论的新发展，以描述静电相互作用，电荷离域和极性在离子中的综合效应；(2)开发新的方法，将量子化学计算和分子模拟结果映射到基础理论模型的参数上；(3)这些新发展在实验性IL系统中的应用。

CBET-0829062McCabeIonic liquids (ILs) are liquids comprised entirely of ions that have melting points at or below room temperature, distinguishing them from high temperature molten salts. ILs are at the forefront in the use of alternative and greener solvents due to their negligible volatility, which minimizes the risk of atmospheric contamination and reduces associated health concerns in comparison with conventional organic solvents. ILs show promise in a wide range of applications from catalysis and biocatalysis, to separations, and photochemical cells. The interest in ILs stems from their unique physical properties, that extend beyond the range of normal molecular solvents, and can include (in addition to no or low volatility) thermal stability, a wide range of temperature over which they are liquid, and the ability to solubilize a wide variety of organic and inorganic materials, including macromolecules. ILs generally consist of a large, organic cation with a weakly coordinating inorganic or organic anion, which frustrates packing and lowers the melting point. The cations and anions each impart different physiochemical properties to the IL and can be substituted to obtain the properties desired, and if needed, functionalized to provide further control. While initial interest in ILs focused primarily on their solvent properties, more recently the potential to use their novel, tunable, physical and chemical properties in the design of new functional materials for a wide range of applications has fueled the interest in ILs. As a result, there has been a great deal of progress to date in IL design; however, much of that progress has been achieved through an empirical approach to property modification. The vast number of possible cation-anion combinations makes it vitally important to be able to rationally predict IL properties based on their constituents. Thus, there is considerable incentive to develop an accurate tool for designing task-specific ILs based upon a physical understanding of the structure and interactions within ILs. The goal of our work is to address this important need through the development of a molecular-based theoretical framework with which to study the thermodynamic properties of ILs. The complex nature of the interactions present in ILs makes their study using computational tools a fundamentally challenging subject. The overall goal is to develop a framework with which to accurately model IL systems and their mixtures with other molecular species, and enable the prediction of their thermodynamic properties. In this work we will focus on developing a molecular-based model for pure ILs, which will lay the foundation for future work on modeling mixtures of ILs and molecular solutes/solvents and the predictive design of task-specific ILs. The approach developed will be optimized against experimental data and ab initio calculations and will enable the prediction of IL properties from the chemical composition, thus eliminating guess work in determining the properties of a given combination of ions and, ultimately, their mixture behavior with molecular species. Specifically, the project e will create a theoretical tool to describe ILs built on the SAFT framework for modeling fluid phase behavior. SAFT, in contrast to the various engineering based equations of state available in the literature, provides a molecular-based approach and is truly unparalleled in its ability to capture the effects of molecular shape, size and interactions into an analytical equation of state. In order to describe the thermodynamic properties of ILs with the molecular-based model outlined above, the PI will develop a theoretical framework for IL systems that combines analytical solutions from integral equation theory (that accurately describe the structure of dipolar and ionic fluids) with the molecular framework of the SAFT-VR approach. The centerpiece of the proposed approach will be the hetero-segmented SAFT model developed by the PI,12 which contrasts with SAFT models that are based on a homo-segmented approach(i.e., each segment in the model chain has the same size and energy of interactionparameters). Intellectual Merit of the Proposed Research - The proposed work will lead to new methods to map properties obtained from quantum chemistry calculations and molecular simulations onto the parameters needed in statistical-mechanics-based models and new developments in liquid state theory. The work will lay the foundation for a significant advance in molecular thermodynamics by providing a predictive IL design methodology based upon a deep physical understanding of IL structure and interactions.Broader Impact of the Proposed Research - The integration of the proposed researchwith the PIs educational activities will ensure that students at Vanderbilt are exposed to, and participate in, the frontiers of molecular modeling and molecular thermodynamics. Participation of minorities will be sought through the NSF TLSAMP4 program at Vanderbilt and high school teachers involved through the PIs participation in a School of Engineering RET site program.Overall plan - AIM 1: A molecular-based model for pure ILsAIM 2: A molecular-based model for mixtures of ILs and molecular solvents/solutesAIM 3: Predictive design of task-specific ILsThe PI will limit the scope of this revised exploratory project to aim one, a molecular-based model for pure ILs since it represents the most challenging and novel part of the work. The work will focused on (1) the derivation and application of new developments in liquid state theory to describe the combined effects of electrostatic interactions, charge delocalization, and polarity in ILs; (2) the development of new methods to map quantum chemistry calculations and molecular simulation results onto the parameters in the underlying theoretical models; and (3) application of these new developments to experimental IL systems.