Snapshot of the bulk structure of ethylammonium nitrate from neutron diffraction and computer simulation. Two interpenetrating networks of polar (red) and apolar groups (grey) can be identified.
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Neutron diffraction and computer simulation are used to study the structure of ionic liquids, which are widely used to conduct chemical reactions.
The Greek philosopher Aristotle once suggested 'No reactions in the absence of solvent.' Whilst chemists have long since demonstrated solid and gas-phase transformations, the vast majority of reactions are still conducted in the liquid phase. The choice of solvent can have a profound influence on reaction outcomes (yields, kinetics, etc.) and yet there are relatively few studies which characterize the structural origin of solvent properties.
In this work, we have examined the bulk structure of ionic liquids – a special class of solvents composed entirely of ions – using neutron diffraction and computer simulation. The results show that ionic liquids self-assemble into bicontinuous nanostructures of polar and apolar domains. This solvent ordering is structurally analogous to thermodynamically stable bicontinuous microemulsions (microemulsions of two immiscible liquids stablised by a third component, such as oil and water stabilised by a surfactant), but with characteristic length scales at least an order of magnitude smaller. Interestingly, the nature of the bicontinuous arrangement could be modified via simple variations in ion structure, meaning that, in principle, the solvation properties of ionic liquids can be designed for particular chemical reactions.
R Hayes, R Atkin (University of Newcastle),
GG Warr (University of Sydney), S Imberti (ISIS)
Research date: August 2011
Contact: Dr Rob Atkin, Rob.Atkin@newcastle.edu.au
Further reading: Hayes et al, Phys. Chem. Chem. Phys, 13 (2011) 13544
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