Thu 25 May 2017 3:30pm (Murdoch University, ECL Postgraduate Suite, 460.2.031)
Structure, Solutes and Surfaces in Ionic Liquids
Rob Atkin
School of Molecular Sciences, The University of Western Australia, WA 6009, Australia
Ionic Liquids (ILs) are a subset of molten salts, distinguished by having melting points below 100 °C. Their low melting points are brought about by weakening electrostatic interactions between the ions and hindering their packing into a crystal lattice. Electrostatic forces are reduced by engineering their molecular structure so that at least one of the ions is large and organic, which increases the distance between neighbouring charged centres, and by delocalising the ionic charge over a large molecular volume. Ionic liquids have some unusual and remarkable properties, including pronounced nanostructures, which is one of their unique, yet unifying, characteristicss.
Neutron diffraction measurements modelled with reverse Monte Carlo simulations will be used to show that ILs have a sponge-like (bicontinuous) nanostructure; IL cation alkyl chains and ionic groups are segregated into domains that percolate throughout the bulk liquid.1-3 A snapshot of the simulation box for ethylammonium nitrate (EAN, a protic IL) is shown in Figure 1 (left). Varying the structure of the ions changes way inter-ionic forces are expressed, which leads to changes in nanostructure. The effect of dissolved water, glycerol and octanol on bulk IL nanostructure will be examined.4,5
High resolution amplitude modulated atomic force microscope images (c.f. Figure 1) will be used to demonstrate how IL nanostructure changes at a solid surface with the ion structure, and the effect of dissolved solutes.6-8 A 20 nm × 20 nm topographic AM-AFM images of the 1-Ethyl-3-methylimidazolium bis(trifluoromethyl- sulfonyl) imide – graphite Stern layer is shown in Figure 1 (middle), with the position of the ions shown in the magnified area in Figure 1 (right). The effect of applying a potential to a conducting solid surface on the IL interfacial nanostructure will also be discussed, and recent results for the spontaneous exfoliation of graphene into an ionic liquid will be described.9
Figure 1. (left) Snap shot of simulation box used to fit neutron diffraction data for EAN. (middle and right) AM-AFM image of the 1-Ethyl-3-methylimidazolium bis(trifluoromethyl- sulfonyl) imide – graphite Stern layer.
References
(1) Atkin, R.; Warr, G. G. J. Phys. Chem. B 2008, 112, 4164.
(2) Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. Physical Chemistry Chemical Physics 2011, 13, 3237.
(3) Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. Angewandte Chemie International Edition 2013, 52, 4623.
(4) Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. Angewandte Chemie International Edition 2012, 51, 7468.
(5) Murphy, T.; Hayes, R.; Imberti, S.; Warr, G. G.; Atkin, R. Physical Chemistry Chemical Physics 2014, 16, 13182.
(6) Elbourne, A.; Voitchovsky, K.; Warr, G. G.; Atkin, R. Chemical Science 2015, 6, 527.
(7) Page, A. J.; Elbourne, A.; Stefanovic, R.; Addicoat, M. A.; Warr, G. G.; Voitchovsky, K.; Atkin, R. Nanoscale 2014, 6, 8100.
(8) Elbourne, A.; McDonald, S.; Voïchovsky, K.; Endres, F.; Warr, G. G.; Atkin, R. ACS Nano 2015, 9, 7608.
(9) Elnourne, A.; Mclean, B. D.; Voïchovsky, K.; Warr, G. G.; Atkin, R J. Phys. Chem. Lett., 2016, 7, 3118
Rob Atkin is a Professor of Chemistry at the University of Western Australia. Rob obtained his PhD from the University of Newcastle (Australia) in 2003 under the supervision of Prof Simon Biggs, then joined the group of Prof. Brian Vincent at Bristol University as a postdoctoral fellow, working on polymer microencapsulation. In 2005 he was awarded an Australian Research Council (ARC) Postdoctoral Fellowship to study surfactant self-assembly in ionic liquids at the University of Sydney in collaboration with Prof Greg Warr. He returned to Newcastle in 2007 as a University of Newcastle Research Fellow, was awarded an ARC Future Fellowship in 2012, and promoted to Professor in 2015. In March 2017 Rob moved to his current position at the University of Western Australia. Rob has published 6 book chapters and 130 journal articles and collaborates with groups in Australia and in the UK, Sweden, Germany, the USA, Japan and France.