Synthesis, self-assembly and liquid structure in deep eutectic solvents

Abstract

Deep eutectic solvents (DES) are a relatively recently reported class of solvent, typically synthesised through the formation of a eutectic mixture between Lewis acidic and Lewis basic components at a particular molar ratio. Over the last two decades, DES have been increasingly investigated as non-aqueous alternative solvents in a wide range of processes. 

In this thesis the synthesis of materials, the self-assembly of surfactant molecules and the liquid structure of DES is explored. The work is presented as three self-contained projects, each related to furthering the understanding of the properties and applications of DES. The possibility of synthesising transition metal oxides and sulfides via a solvothermal synthesis method was first explored, together with some characterisation of the morphology and electrochemical performance of the products. For the synthesis of oxides
in choline chloride:urea, it was shown that reactions typically proceed only when water is added to the DES. The reactions attempted during this project were summarised and the limitations of the solvothermal method were discussed. A polymeric DES based on polyethylene glycol-200 was investigated for the synthesis of mixed Co-Fe sulfides. The catalytic activity of the samples towards the hydrogen evolution reaction (HER) was assessed using a three-electrode electrolytic cell.

In the second part of this project, the self assembly of cationic alkyltrimethylammonium bromide surfactants, which are insoluble in choline chloride:urea, was successfully demonstrated in a three component system comprising choline chloride, urea and glycerol. The physiochemical properties of the three component DES were characterised, and the factors which influence the solubility and micellisation of C₁₆TAB was investigated using small-angle neutron scattering (SANS). It was determined that the degree of elongation in the micelles could be controlled by varying the urea:glycerol ratio in the DES, and this was attributed to the degree of solubility of the surfactant counterion in each solvent composition. The effect of water and metal ion addition on the DES was also discussed. Finally, experiments were also carried out to explore the use of these surfactant/DES mixtures for the synthesis of metal oxide materials.

In the last section of this this thesis, the liquid structure of the ChCl:urea:glycerol DES was investigated using total neutron scattering, in order to characterise the intermolecular interactions present within the system and determine the effect on the structure of varying the component ratio. The effect of water and metal ion addition on the structure was also investigated. Empirical Structure Potential Refinement (EPSR) was used as an analysis method to extract key parameters from the experimental data.

Date of Award	29 Mar 2023
Original language	English
Awarding Institution	University of Bath
Supervisor	Karen Edler (Supervisor), Hannah Leese (Supervisor), Frank Marken (Supervisor) & Salvador Eslava (Supervisor)