Layered structure of room temperature ionic liquids in microemulsions by multinuclear NMR spectroscopic studies.

R DARIO FALCONE; B. BARUAH; E. GAIDAMAUSKAS; C. R. RITHNER; N. MARIANO CORREA; JUANA J. SILBER; DEBBIE C . CRANS; NANCY E. LEVINGER

CHEMISTRY-A EUROPEAN JOURNAL

WILEY-V C H VERLAG GMBH

Año: 2011 vol. 17 p. 6837 - 6846

0947-6539

Microemulsions form in mixtures of polar, nonpolar and amphiphilic molecules. Typical microemulsions employ water as the polar phase. However, microemulsions can form with a polar phase other than water, which hold promise to diversify the range of properties, and hence utility, of microemulsions. Here microemulsions formed using a room temperature ionic liquid (RTIL) as the polar phase are created and characterized using multinuclear NMR spectroscopy. 1H, 11B and 19F NMR are applied to explore differences between microemulsions formed using 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim+][BF4-]) as the polar phase with a cationic surfactant benzylhexadecyldimethylammonium chloride (BHDC) and a nonionic surfactant Triton X-100 (TX-100). NMR spectroscopy shows distinct differences in the behavior of the RTIL as the charge of the surfactant head group varies in the different microemulsion environments. Minor changes in the chemical shifts were observed for the [bmim+] and [BF4-] system in the presence of TX-100 suggesting the surfactant and the ionic liquid are separated in the microemulsion .  The large changes in spectroscopic parameters observed are consistent with microstructure formation with layering of [bmim+] and [BF4-] and migration of Cl- within the BHDC microemulsions.  Comparisons to NMR results for related ionic compounds in organic and aqueous environments as well as literature studies assist the development of a simple organizational model for these microstructures.