João A. P. Coutinho
CICECO, Department of Chemistry, University of Aveiro, Portugal
jcoutinho@ua.pt
Keywords
Surface tension, Surface crystallization, Cloud Points, Hydrotropy, Applications.
Many think of ionic liquids as molten salts but, if the nanostructuration is what makes an ionic liquid distinct, they are indeed closer to structured fluids such as surfactants and block copolymers than to molten salts or conventional liquids.
Much can be gained from the study of the surface of ionic liquids, and some interesting phenomena of surface structuration, including surface crystallization, and the production of nanofibers of cellulose by electrospinning by controlling the surface tension of the solvent will be addressed.
If their surface shows a broad range of interesting and unique features, the bulk of these fluids, or their aqueous solutions, can be even more surprising. From the self-assembly in liquid crystals to the interfacial behavior and formation of complex aggregates, alone or in interaction with other surfactants and block copolymers they can produce a rich variety of phase diagrams, and be used to manipulate the CMCs and cloud points of a range of compounds. Yet these surfactant ionic liquids are more than just curiosities, and applications from the superactivation of enzymes to the extraction of biomolecules, such as fluorescent proteins, from biomass will be presented.
As for common surfactants, for which small chain lengths prevent the formation of micelles but allow them to act as solvents and hydrotropes in aqueous solution, the nanostructure, even if incomplete, produces dramatic changes in the properties of their aqueous solutions, allowing the solvation of many different compounds and the appearance of novel mechanisms of dissolution, intermediate between the conventional solvation and micelle dissolution: the poorly understood hydrotropic realm. The action of ionic liquids as hydrotropes will be presented for a variety of molecules, from simple phenolic compounds to alkaloids, complex drugs and polymeric lignin, and the hydrotropic dissolution mechanism discussed phenomenologically, and by Molecular Dynamics and the Kirkwood-Buffer theory.
It is expected that this overview of the work developed in our laboratory, covering from the basic molecular phenomena to applications with industrial potential, may prompt a swerve in the view of ionic liquids from molten salts to ionic structured fluids more akin to surfactants, and instill the desire for novel studies and approaches in the use of ionic liquids.
João A. P. Coutinho is a Full Professor at the Chemistry Department of University of Aveiro, Portugal where he is vice-director of CICECO – Aveiro Institute of Materials. He studied Thermodynamics and Petroleum Technology at Technical University of Denmark where he got his PhD in Chemical Engineering in 1995. Since 1997 he leads a multidisciplinary research team that focuses on a range of different subjects from the petroleum production in non-conventional reservoirs, to the production and formulation of biofuels, and the development of novel separation processes for the biorefinery. Currently he strives to apply ionic liquids to these processes and is trying to better understand their physical-chemical behavior for that purpose.