Switchable Solvents & Surfactants
"Switchable" (adj.) to be able to reversibly switch "on" and "off", or switch between one property and another, when a trigger is applied. Imagine a solvent that could switch reversibly from one kind of liquid to a very different kind of liquid, upon command. We have found three classes of switchable solvents, as shown below.
Switchable-Polarity Solvents
These have low polarity until they are exposed to an atmosphere of CO2, at which point they change into high-polarity ionic liquids. The polarity difference is large enough that many solutes are soluble in only one form of the solvent. The process is reversed by removal of the CO2 from solution. These liquids are also extremely efficient greenhouse gas-capture agents.
Further Reading (Switchable Solvents)
» P. G. Jessop, D. J. Heldebrant, L. Xiaowang, C. A. Eckert, C. L. Liotta, Nature, 2005, 436, 1102.
» L. Phan, J. R. Andreatta, L. K. Horvey, C. F. Edie, A.-L. Luco, A. Mirchandi, D. J. Darensbourg, P. G. Jessop, J. Org. Chem., 2008, 73, 127.
» L. Phan, X. Li, D. J. Heldebrant, R. Wang, D. Chiu, E. John, H. Huttenhower, P. Pollet, C. A. Eckert, C. L. Liotta, P. G. Jessop, Ind. Eng. Chem. Res., 2008, 47, 539.
Further Reading (Gas Capture)
» D. J. Heldebrant, C. R. Yonker, P. G. Jessop, L. Phan, "Reversible Uptake of COS, CS2 and SO2: Ionic liquids with O-alkylxanthate, O-alkylthiocarbonyl and O-alkylsulfite Anions", Chem. Eur. J., 2009, 15, 7619-7627.
» D. J. Heldebrant, C. R. Yonker, P. G. Jessop, L. Phan, "Organic liquid CO2 Capture Agents with High Gravimetric CO2 Capacity," Energy & Environ. Science, 2008, 1, 487-493.
Switchable-Hydrophobicity Solvents
These are liquid solvents that are normally so hydrophobic that they have very little miscibility with water and form a biphasic mixture when mixed with water. However, when exposed to CO2, these solvents become very hydrophilic and completely miscible with water. Therefore these solvents can behave like hexane but be easily removed, by extraction with carbonated water, without distillation.
Further Reading
» P. G. Jessop, L. Phan, A. Carrier, S. Robinson, C. J. Dürr and J. R. Harjani, "A Solvent having Switchable Hydrophilicity", Green Chemistry, 2010, 12, 809-814.
Switchable Water
An aqueous solution of an uncharged additive has an ionic strength of zero and is miscible with an organic liquid such as THF. However, after CO2 is introduced, the additive changes to a salt, raising the ionic strength, and forcing the THF out of solution. Removal of the CO2 by air or heat reverses the process. This represents a reversible method for “salting-out” of organic compounds from water.
Further Reading
Switchable Surfactants
Imagine a surfactant that stabilizes emulsions but could switch reversibly to a demulsifier, upon command. Emulsions could be stabilized while they are wanted and then destabilized when the emulsion is no longer wanted. We have found a surfactant that is stable in the presence of CO2 but converts to a demulsifier if the CO2 is flushed away with air. The initial results were published in the journal Science (2006, 313, 958). This technology has great potential for applications in the energy industry, cleaning, fine chemical manufacture, polymers, coatings, and many other areas.
Further Reading
» M. Mihara, M. Cunningham, and P. G. Jessop "Redispersible Polymer Colloids using Carbon Dioxide as an External Stimulus", Macromolecules, 2011, 44, 3688-3693.
» C. I. Fowler, C. Muchemu, R. E. Miller, L. Phan, O'Neill, C., M. F. Cunningham, and P. G. Jessop "Emulsion Polymerization of Styrene and Methyl Methacrylate using Cationic Switchable Surfactants", Macromolecules, 2011, 44, 2501-2509.
» J. R. Harjani, C. Liang, P. G. Jessop, "A Synthesis of Acetamidines", J. Org. Chem., 2011, 76, 1683-1691.
» Y. Liu, P. G. Jessop, M. Cunningham, C. A. Eckert, C. L. Liotta, "Switchable Surfactants," Science, 2006, 313, 958-960.
