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

CBET-0829062 McCabeIonic liquids（IL）是完全由熔点等于或低于室温的离子组成的液体，将它们与高温熔融盐区分开来。离子液体由于其可忽略的挥发性而处于替代和绿色溶剂使用的最前沿，与传统有机溶剂相比，这种挥发性最大限度地减少了大气污染的风险并减少了相关的健康问题。离子液体在从催化和生物催化到分离和光化学电池的广泛应用中显示出前景。对IL的兴趣源于其独特的物理性质，其延伸超出正常分子溶剂的范围，并且可以包括（除了无挥发性或低挥发性之外）热稳定性、它们为液体的宽范围温度以及溶解各种有机和无机材料（包括大分子）的能力。离子液体通常由大的有机阳离子和弱配位的无机或有机阴离子组成，这阻碍了堆积并降低了熔点。阳离子和阴离子各自赋予IL不同的生理化学性质，并且可以被取代以获得所需的性质，并且如果需要，可以被官能化以提供进一步的控制。虽然最初对离子液体的兴趣主要集中在它们的溶剂性质上，但最近在设计用于广泛应用的新功能材料中使用它们的新颖的、可调节的物理和化学性质的潜力已经激发了对离子液体的兴趣。因此，迄今为止在IL设计方面已经取得了很大的进展;然而，大部分进展是通过对属性修改的经验方法实现的。大量可能的阳离子-阴离子组合使得能够基于其成分合理地预测IL性质变得至关重要。因此，有相当大的动机，开发一个准确的工具，设计特定任务的离子液体的基础上的物理理解的结构和内部的离子液体的相互作用。我们工作的目标是通过发展一个以分子为基础的理论框架来研究离子液体的热力学性质，以满足这一重要需求。离子液体中存在的相互作用的复杂性质使得使用计算工具进行研究成为一个具有根本挑战性的课题。总体目标是开发一个框架，准确地模拟IL系统及其与其他分子物种的混合物，并能够预测其热力学性质。在这项工作中，我们将专注于开发一个基于分子的纯离子液体的模型，这将奠定基础，为未来的工作建模的离子液体和分子溶质/溶剂的混合物和特定任务的离子液体的预测设计。开发的方法将针对实验数据和从头计算进行优化，并将能够从化学组成预测IL属性，从而消除了在确定给定离子组合的属性时的猜测工作，并最终确定它们与分子物种的混合物行为。具体来说，项目e将创建一个理论工具来描述建立在SAFT框架上的离子液体，用于模拟流体相行为。SAFT与文献中的各种基于工程的状态方程相反，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分析状态方程中的能力方面确实无与伦比。 为了用上述基于分子的模型描述离子液体的热力学性质，PI将开发一个离子液体系统的理论框架，该框架将积分方程理论的分析解（准确描述偶极和离子液体的结构）与SAFT-VR方法的分子框架相结合。所提出的方法的核心将是由PI开发的异质分段SAFT模型，12这与基于同质分段方法的SAFT模型（即，模型链中的每个段具有相同的尺寸和相互作用能量参数）。拟议研究的智力价值-拟议的工作将导致新的方法来映射从量子化学计算和分子模拟获得的属性到基于物理力学的模型和液态理论的新发展所需的参数。这项工作将奠定基础，为一个显着的进步，在分子热力学通过提供一个预测IL设计方法的基础上，深入的物理理解IL结构和interaction.Broader影响的拟议研究-拟议的研究与PI教育活动的整合将确保学生在范德比尔特接触，并参与，分子建模和分子热力学的前沿。少数民族的参与将通过范德比尔特的NSF TLSAMP 4项目寻求，高中教师将通过PI参与工程学院的RET现场项目寻求。总体计划- AIM 1：纯IL的分子模型AIM 2：IL和分子溶剂/溶质混合物的分子模型AIM 3：特定任务ILs的预测设计PI将把这个修订后的探索性项目的范围限制在目标一，纯ILs的分子模型，因为它代表了工作中最具挑战性和新颖性的部分。工作重点是：（1）推导和应用液态理论的新发展来描述离子液体中静电相互作用、电荷离域和极性的综合效应;（2）发展新的方法来将量子化学计算和分子模拟结果映射到基础理论模型中的参数上;以及（3）这些新发展在实验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.