Molecular level insight to solvents

Abstract

With the increasing demand for resources in modern society and the impacts of climate change, there is a growing need for innovative and environmentally friendly solutions. Achieving sustainability in chemistry and materials science is crucial for enhancing human well-being and reducing energy consumption. In this context, solvents and their effects play a vital role in daily life, various chemical processes, as well as many research fields. This thesis focuses on understanding tunable classes of solvents, such as deep eutectic solvents (DES) and ionic liquids (IL) and developing new computational techniques like Hybrid Monte Carlo. These efforts aim to advance the overarching goal of sustainability in chemistry. <br /> Despite the growing number of studies on DESs and ILs their working principles at the molecular level remain not fully understood. Multiscale theoretical approaches combined with suitable analysis tools are essential methods for gaining a more detailed insight into the microscopic behavior of solvents and solvent effects. Therefore, all projects were conducted from a computational chemistry perspective, employing various multiresolution and multiscale simulation methods such as classical molecular dynamics and ab initio molecular dynamics. In addition, a hybrid Monte Carlo method was developed and implemented. Insights into the hydrogen bonding network's dependence on composition and water presence by ab initio molecular dynamics simulations are provided for the deep eutectic solvents mixture. <br /> This study could show that there is no strong dependency on the molecular level interactions on molar stoichiometry. This result implies DES are not be restricted to fixed proportions between the hydrogen bond acceptor and hydrogen bond donor. Based on this finding, the microheterogeneity in deep eutectic solvents and its tunability are investigated revealing the impact of cation size on microheterogeneity and nanostructure in these solvents. Furthermore, solvent effects for CO₂ absorption, cellulose fiber, and titanocene catalyst are investigated. In the context of CO₂ absorption, the choline chloride: ethylene glycol mixture demonstrated potential as a CO₂ absorbent. Ab initio molecular dynamics simulations uncovered the effects of anions, cations, and hydrogen bond donors on CO₂ solvation, emphasizing DESs' advantages over other liquids. The MD simulation of cellulose solvation in DESs highlights the influence of anion interactions on cellulose structure. Theoretical advancements and challenges for investigating titanocene catalysis in ILs are discussed as well, underscoring the importance of selecting an accurate electronic structure method for studying radical species. The complexity of theoretically handling radicals within ILs through ab initio molecular dynamics simulations, necessitates further methodological advancements. <br /> Finally, a hybrid Monte Carlo method with a special focus on investigating phase transition is investigated and developed, specifically the argon fluid solidification. Hybrid Monte Carlo method showed improved sampling compared to conventional molecular dynamics, making them a promising approach for investigating other solvents. <br /> To summarize, this thesis provides new insights into deep eutectic solvents, ionic liquids, and their solvent effects in various applications from a theoretical perspective. Furthermore, effective simulation techniques for these solvents are developed and validated.