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Title: Mixtures of ionic liquids
Author: Niedermeyer, Heiko Jannes
ISNI:       0000 0004 2741 4908
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2012
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Ionic liquids have gained a reputation as ‘designer solvents’ due to the wide range of properties that are accessible and the fine degree of ‘tuning’ allowed by varying the constituting ions. To further widen the parameter space, yet allow the prediction of properties, mixtures of ionic liquids are analysed in this project. An extensive literature review is performed, covering the full range of available publications on this subject at the time of writing. The available literature is extended by original research on mixtures covering a range of structurally different anions and cations that have not been reported in mixtures before. Chemical and physical properties such as conductivity, viscosity, density and solvent properties are evaluated. The physical properties are found to behave largely ideally with few exceptions, while the solvent properties of mixtures are found to behave in a systematic manner according to simple equilibrium laws. A potential explanation for the dependence of the H-bond acidity of ionic liquid cations on the basicity of the corresponding anion based on multiple available acidic protons of the cation is discussed and evaluated. Computational methods to predict the acidity and basicity parameters α and β of pure ionic liquids are developed and evaluated. For the H-bond acidity α the electrostatic potential, complex formation with NCH and electronic excitations of the complex with Reichardt’s Dye are found successful. For β, properties of the complex with HF are found to correlate well with the H-bond basicity. The properties of a siloxane substituted cation are analysed by DFT calculations to explain the low viscosity of the corresponding ionic liquids. The cation is found to form intramolecular interactions and have lowered barriers for the movement of the substituent, thus minimising cation–cation interactions, increasing entropy and facilitating the movement of anions.
Supervisor: Welton, Tom ; Hunt, Patricia Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral