Surface structures of binary mixtures of imidazolium-based ionic liquids using high-resolution Rutherford backscattering spectroscopy and time of flight secondary ion mass spectroscopy

Kaoru Nakajima; Motoki Miyashita; Motofumi Suzuki; Kenji Kimura

doi:10.1063/1.4838376

Surface structures of binary mixtures of imidazolium-based ionic liquids using high-resolution Rutherford backscattering spectroscopy and time of flight secondary ion mass spectroscopy

J Chem Phys. 2013 Dec 14;139(22):224701. doi: 10.1063/1.4838376.

Authors

Kaoru Nakajima¹, Motoki Miyashita¹, Motofumi Suzuki¹, Kenji Kimura¹

Affiliation

¹ Department of Micro Engineering, Kyoto University, Kyoto-daigaku-Katsura, Nishikyo, Kyoto 615-8549, Japan.

PMID: 24329076
DOI: 10.1063/1.4838376

Abstract

Surface structures of binary mixtures of imidazolium-based ionic liquids having a common anion (bis(trifluoromethanesulfonyl)imide ([TFSI]), namely [C2MIM]1-x[C10MIM]x[TFSI] (x = 0.5 and 0.1), are studied using high-resolution Rutherford backscattering spectroscopy (HRBS) and time of flight secondary ion mass spectroscopy (TOF-SIMS). Although both measurements show surface segregation of [C10MIM] the degrees of the segregation are different. The surface fraction xsurf of [C10MIM] is estimated to be 0.6 ± 0.05 and 0.18 ± 0.02 by HRBS for x = 0.5 and 0.1, respectively. On the other hand, TOF-SIMS indicates much stronger surface segregation, namely xsurf = 0.83 ± 0.03 and 0.42 ± 0.04 for x = 0.5 and 0.1, respectively. The observed discrepancy can be attributed to the difference in the probing depth between HRBS and TOF-SIMS. The observed surface segregation can be roughly explained in terms of surface tension.