Ryan Stefanovic


PhD Project: "Bulk & Interfacial Structure in New Classes of Ionic Liquids

My PhD research focuses on molecular simulations of the interfacial structure of various Ionic Liquids (ILs) on solid surfaces using density functional theory and density functional tight binding. ILs are pure salts that are liquid below 100C (although ILs of interest have melting points below room temperature). Due to their ionic nature and interesting interfacial structure, ILs have possible future applications in electrochemistry, in particular as lubricants between electrical contacts. Combining these modelled systems with data retrieved using Atomic Force Microscopy (AFM) has enabled a better understanding of the structuring of ILs at a molecular level, as AFM is only able to determine general lateral structure of a surface, not the particular components that order at the surface.

reline.png

Recent work has been into the relatively new class of solvents, called Deep Eutectic Solvents (DESs). DESs are mixtures composed of two or more components that, in specific ratios, exhibit a significant drop in the melting temperature of the mixture. This phenomenon is most significantly observed in quaternary ammonium salts, in particular the Choline Chloride (ChCl) – Urea system, the focus of my work. Choline Chloride and Urea have melting points of 302C and 133C respectively. However, 1:2 molar ratio of Choline Chloride and Urea has a melting point of 12C. Due to their ionic nature and reduced melting temperature, DESs have properties similar to that of ILs. Unlike ILs however, DESs are composed of cheap, organic constituents which are environmentally friendly and bio-degradable, an important quality for any large scale chemical. Whilst it is believed that this reduced melting temperature is the product of a disruption of the lattice structure, in particular the hydrogen bonding networks formed between Urea-Urea and ChCl-ChCl, very little computational work has been performed in this area. My work has focused on applying DFTB to these systems, to determine how the bulk structure of this eutectic mixture forms allowing for the reduced melting temperature. Further work will be undertaken at a variety of interfaces, including HOPG to determine how, if at all, the overall structure is affected.

Optimised structure of a four-ion-pair choline-chloride urea cluster (“reline”). Red = O, Blue = N, 

White = H, Aqua = C, Green = Cl


Publications

1. Chen, Z., McLean, B., Ludwig, M., Stefanovic, R., Warr, G. G., Webber, G. B., Page, A. J., Atkin, R., “Nanostructure of Deep Eutectic Solvents at the Graphite Electrode Interface as a Function of Potential”, Journal of Physical Chemistry C, 2016, 120, 2225-2233.

2.  McLean, B., Li, H., Stefanovic, R., Wood, R. J., Ueno, K., Watanabe, M., Warr G. G., Page, A. J., Atkin, R., "Nanostructure of [Li(G4)]TFSI and [Li(G4)]NO3 solvate ionic liquids at HOPG and Au(111) electrode interfaces as a function of potential", Physical Chemistry Chemical Physics, 2014, 17, 325-333.

3.  Addicoat, M. A., Stefanovic, R., Webber, G., Atkin, R., Page, A. J., "Assessment of the density functional tight binding method for protic ionic liquids", Journal of Chemical Theory and Computation, 2014, 10, 4633-4643.

4.  Page, A. J., Elbourne, A., Stefanovic, R., Addicoat, M. A., Warr, G., Voitchovsky, K., Atkin, R., "3-dimensional atomic scale structure of the ionic-liquid graphite interface elucidated by combined AM-AFM and quantum chemical simulations", Nanoscale, 2014, 6, 8100-8106

© 2015