On 5 October at 12.15 Karl Karu will defend his doctoral thesis „Computer modeling of ionic liquid properties and behavior at the molecular and interfacial levels“.
Supervisors:
Associate Professor Vladislav Ivaništšev, Institute of Chemistry, University of Tartu Associate Professor Kaija Põhako-Esko, Institute of Chemistry, University of Tartu
Opponent:
Associate Professor Naoya Nishi, Doctor of Engineering, Graduate School of Engineering, Kyoto University, Japan
Summary:
Most familiar liquids are made of neutral molecules. Ionic liquids, by contrast, are salts composed entirely of positively and negatively charged ions that can stay liquid near room temperature. Changing either ion creates an enormous range of possible liquids whose properties can be tuned for a specific task. Because they barely evaporate and can remain stable at high temperatures and voltages, ionic liquids are promising for batteries, supercapacitors, sensors, greener chemical processes and soft actuators. This flexibility also creates a practical problem: testing every possible ion combination in the laboratory would be slow and expensive. This thesis developed computational workflows that serve as virtual screening tools for ionic liquids. Quantum chemical calculations were used to describe how strongly ions interact and how readily they may decompose. Molecular dynamics simulations followed the collective motion of many ions in the liquid and their organization next to charged electrodes. Machine learning models helped extend predictions to larger sets of candidates. Together, these methods estimated melting points, actuator deformation, electrochemical stability and changes in interfacial ion layers. A corrected density functional achieved good accuracy at substantially lower computational cost than demanding reference calculations. A new simulation workflow predicted the melting points of low-toxicity, biodegradable choline-based ionic liquids without requiring their crystal structures. The interfacial analysis showed that, under normal operating conditions, ions near an electrode are more likely to overscreen than to crowd. Finally, combining electrochemical stability with ease of ion motion produced a practical map for identifying promising electrolytes. These tools can reduce the number of laboratory experiments needed and guide the design of safer, more sustainable materials for energy and sensing technologies.
