DOI: 10.1002/chem.201200682 Ethanol-Assisted, Few Nanometer Water-In-Ionic Liquid Reverse Micelle Formation by a Zwitterionic Surfactant Rewa Rai, [a] Shubha Pandey, [b] Sheila N. Baker, [c] Sambhav Vora, [d] Kamalakanta Behera, [a] Gary A. Baker,* [b] and Siddharth Pandey* [a] Microemulsions—optically isotropic, transparent, and thermodynamically-stable dispersions of two or more immis- cible liquids which are stabilized by an adsorbed surfactant (or emulsifier) layer at the liquid–liquid interface—have nu- merous applications across a number of fields. [1] Depending upon the natures of the components, these specific nano- scale aggregates may comprise oil-in-water (o/w) or water- in-oil (w/o) microemulsions. The o/w microemulsion shares many features of normal micelles in water and thus enjoys similar applications. [1c] The w/o microemulsion, on the other hand, can contain exceptionally high amounts of water within a hydrophobic “oil” phase, with the specific size and shape of the water pools being controlled by the ratio of the water-to-surfactant concentration (w 0 ) and, of course, the identities of the surfactant and the continuous oil phase. [1] Commercially important uses of w/o microemulsions include their use in dry cleaning processes, as floor polishers and cleaners, in personal care products, in pesticide formulations, in cutting oils, and biocatalysis, to name a few. [1] Significant research carried out on w/o systems has been motivated by their potential use in mobilizing petroleum trapped in porous sandstone for enhanced oil recovery even under con- ditions of slow flow or low pressure gradients. [1] Another key industrial application of w/o microemulsions is for the synthesis of polymers; w/o microemulsion polymerization is a complex heterogeneous process in which the particle sta- bility is affected by the amount and type of surfactant as well as the properties of the dispersing medium. [1b] A major problem with conventional w/o microemulsions, however, is that they contain large amounts of organic sol- vent that often contribute detrimental effects to human health and produce significant waste disposal issues. Thus, alternative bulk oil phases that do not share these draw- backs are desirable. Furthermore, the typical organic sol- vents used as the oil phase offer a limited range in physico- chemical properties. These facts understandably restrict the practical application of w/o microemulsions, accounting for the search for alternative solvents, including supercritical carbon dioxide. [2] Due to their reputed environmentally benign nature—a designation not wholly earned—along with several attractive, demonstrated physicochemical prop- erties (e.g., low volatility, high thermal stability, broad liq- uidus, broad electrochemical windows), ionic liquids (ILs) are burgeoning alternatives to traditional organic solvents. [3] Because water-immiscible ILs share certain solvent traits with those of conventional oil phases, they suggest compel- ling suitability for the formation of novel water-in-ionic liquid (w/IL) microemulsions. Given the easily tailored and striking properties of ILs, w/IL microemulsions add another dimension of curiosity and colloidal flexibility in the sense that w/IL microemulsions may demonstrate favorably en- hanced, unusual, or unforeseen properties in comparison to conventional w/o microemulsions. While few in number, re- searchers have begun to explore in earnest w/IL microemul- sions, including their fundamental characterization and varied application. [4] Attempts to form w/IL microemulsions have demonstrat- ed that their formation is generally hindered by the immisci- bility of many conventional surfactants in ILs, [5] and as a result, all reports to date on w/IL microemulsions comprise use of nonionic surfactants, [4] with no report on w/IL micro- ACHTUNGTRENNUNGemulsions utilizing a zwitterionic surfactant. In this Commu- nication, we report the first example of a w/IL microemul- sion generated using a zwitterionic surfactant. Studying the surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propane- sulfonate (commonly known as dodecyl sulfobetaine, SB-12) in two different exemplary water-immiscible ILs systems (1- butyl-3-methylimidazolium hexafluorophosphate, [bmim]- ACHTUNGTRENNUNG[PF 6 ], and 1-ethyl-3-methylimidazolium bis(trifluoromethyl- sulfonyl)imide, [emim]ACHTUNGTRENNUNG[Tf 2 N]; Scheme 1), we found that the addition of a critical amount of ethanol as co-polar phase is [a] R. Rai, Dr. K. Behera, Prof. S. Pandey Department of Chemistry Indian Institute of Technology Delhi, Hauz Khas New Delhi–110016 (India) E-mail: sipandey@chemistry.iitd.ac.in [b] Dr. S. Pandey, Prof. G.A. Baker Department of Chemistry University of Missouri-Columbia Columbia, MO 65211 (USA) [c] Prof. S. N. Baker Department of Chemical Engineering University of Missouri-Columbia Columbia, MO 65211 (USA) [d] Dr. S. Vora Department of Chemistry Sir P. T. Sarvajanik College of Science Athwalines, Surat–395007 (India) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201200682. Chem. Eur. J. 2012, 00,0–0  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! ÞÞ &1& COMMUNICATION