Solidification of Ionic Liquids: Theory and Techniques

Anja-Verena Mudring

doi:10.1071/CH10017

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Solidification of Ionic Liquids: Theory and Techniques

Anja-Verena Mudring ^A

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^A Anorganische Chemie I – Festkörperchemie und Materialien, Ruhr-Universität Bochum, D-44780 Bochum, Germany. Email: anja.mudring@rub.de

Anja-Verena Mudring studied chemistry at the Rheinische Friedrich Wilhelms-Universität in Bonn. Her thesis, which was carried out at the Max Planck Institute for Solid-State Research in Stuttgart, focussed on the chemistry of anionic gold (2001). As a Feodor Lynen fellow of the Alexander von Humboldt Foundation she joined, from 2001 to 2003, the research group of John Corbett at Iowa State University and Ames Laboratory where she investigated the chemical bonding in Zintl compounds and reduced rare earth halides. With a Liebig fellowship, she established a young researcher group at the Universität zu Köln in 2003 where she finished her Habilitation on the ‘Chemistry of 6th Period Elements’ in 2006. In 2006, she became a Professor for inorganic and materials chemistry at the Ruhr-Universität Bochum. She was also an Iowa State faculty affiliate from 2005 to 2006 and since 2008, she has been an adjunct professor at the University of Alabama in Tuscaloosa. She is the author of more than 100 publications and has received numerous awards such as the Dozentenstipendium. In 2008, she was awarded an ERC starting grant for the exploration of ionic liquids for materials synthesis.

Australian Journal of Chemistry 63(4) 544-564 https://doi.org/10.1071/CH10017
Submitted: 12 January 2010 Accepted: 15 March 2010 Published: 1 April 2010

Abstract

Ionic liquids (ILs) have become an important class of solvents and soft materials over the past decades. Despite being salts built by discrete cations and anions, many of them are liquid at room temperature and below. They have been used in a wide variety of applications such as electrochemistry, separation science, chemical synthesis and catalysis, for breaking azeotropes, as thermal fluids, lubricants and additives, for gas storage, for cellulose processing, and photovoltaics. It has been realized that the true advantage of ILs is their modular character. Each specific cation–anion combination is characterized by a unique, characteristic set of chemical and physical properties. Although ILs have been known for roughly a century, they are still a novel class of compounds to exploit due to the vast number of possible ion combinations and one fundamental question remains still inadequately answered: why do certain salts like ILs have such a low melting point and do not crystallize readily? This Review aims to give an insight into the liquid–solid phase transition of ILs from the viewpoint of a solid-state chemist and hopes to contribute to a better understanding of this intriguing class of compounds. It will introduce the fundamental theories of liquid–solid-phase transition and crystallization from melt and solution. Aside form the formation of ideal crystals the development of solid phases with disorder and of lower order like plastic crystals and liquid crystals by ionic liquid compounds are addressed. The formation of ionic liquid glasses is discussed and finally practical techniques, strategies and methods for crystallization of ionic liquids are given.

Acknowledgements

A.V.M. wishes to thank the Fonds der Chemischen Industrie for a Dozentenstipendium and the Deutsche Forschungsgemeinschaft for support within the priority program SPP 1191 ‘Ionic Liquids’. Dr Bert Mallick is acknowledged for compiling DSC thermograms from his doctoral thesis and Dr Slawomir Pitula is thanked for taking pictures during the heterogeneous crystallization of [Hmim][Tf₂N].

References

Solidification of Ionic Liquids: Theory and Techniques

Abstract

Acknowledgements

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