Ionic multilayers at the free surface of an ionic liquid, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide, probed by x-ray reflectivity measurements

The presence of ionic multilayers at the free surface of an ionic liquid, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide ([TOMA(+)][C4C4N-)], extending into the bulk from the surface to the depth of similar to 60 angstrom has been probed by x-ray reflectivity measurements. The reflectivity versus momentum transfer (Q) plot shows a broad peak at Q similar to 0.4 angstrom(-1), implying the presence of ionic layers at the [TOMA(+)][C4C4N-] surface. The analysis using model fittings revealed that at least four layers are formed with the interlayer distance of 16 angstrom. TOMA(+) and C4C4N- are suggested not to be segregated as alternating cationic and anionic layers at the [TOMA(+)][C4C4N-] surface. It is likely that the detection of the ionic multilayers with x-ray reflectivity has been realized by virtue of the greater size of TOMA(+) and C4C4N- and the high critical temperature of [TOMA(+)] [C4C4N-]. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3398029]