title: Fluorescence correlation spectroscopy evidence for structural heterogeneity in ionic liquids.
abstract: In this work, we provide new experimental evidence for chain length-dependent self-aggregation in room temperature ionic liquids (RTILs) using fluorescence correlation spectroscopy (FCS). In studying a homologous series of N-alkyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide, [C(n)MPy][Tf(2)N] RTILs of varying alkyl chain length (n = 3, 4, 6, 8, and 10), biphasic rhodamine 6G solute diffusion dynamics were observed; both the fast and slow diffusion coefficients decreased with increasing alkyl chain length, with the relative contribution from slower diffusion increasing for longer-chain [C(n)MPy][Tf(2)N]. We propose that the biphasic diffusion dynamics originate from self-aggregation of the nonpolar alkyl chains in the cationic [C(n)MPy](+).
authors.affiliation: Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Jianchang
authors.initials: J
authors.lastname: Guo
authors.forename: Gary A
authors.initials: GA
authors.lastname: Baker
authors.forename: Patrick C
authors.initials: PC
authors.lastname: Hillesheim
authors.forename: Sheng
authors.initials: S
authors.lastname: Dai
authors.forename: Robert W
authors.initials: RW
authors.lastname: Shaw
authors.forename: Shannon M
authors.initials: SM
authors.lastname: Mahurin