Surface segregation in a binary mixture of ionic liquids: Comparison between high-resolution RBS measurements and moleculardynamics simulations

Abstract

Surface structure of equimolar mixture of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([CCIm][TfN]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([CCIm][BF]) is studied using high-resolution Rutherford backscattering spectroscopy (HRBS) and molecular dynamics (MD) simulations. Both HRBS and MD simulations show enrichment of [TfN] in the first molecular layer although the degree of enrichment observed by HRBS is more pronounced than that predicted by the MD simulation. In the subsurface region, MD simulation shows a small depletion of [TfN] while HRBS shows a small enrichment here. This discrepancy is partially attributed to the artifact of the MD simulations. Since the number of each ion is fixed in a finite-size simulation box, surface enrichment of particular ion results in its artificial depletion in the subsurface region.

Determining the composition of the vacuum–liquid interface in ionic-liquid mixtures

“…Only an isolated report using ARXPS has suggested an absence of non-stoichiometry surface segregation for related mixed long and short chain systems. 13 However, this may not solely be the result of an intrinsic larger penetration depth for the ARXPS, with the interpretation of the data having been questioned by Nakajima et al 29 N H'B" cation), 28 and independent LEIS measurements by Lovelock on related mixed-anion systems, 30 More subtly, Fig. 10 also implies that the [C12mim] + cations are oriented towards vacuum, because sites further from the Nterminus are found at progressively larger distances on average.…”

“…These are attractive for potential applications because the properties can be fine-tuned by simply varying the mixing ratio, rather than having to synthesize a large number of chemically distinct compounds. Their surface properties have begun to be examined by direct techniques, 13,15,[27][28][29][30] but the data remain relatively sparse. In particular, there have been no systematic attempts to investigate the relationships between these direct measures and the more-established but indirect measurement of surface tensions.…”

Temperature‐Dependent Surface Enrichment Effects in Binary Mixtures of Fluorinated and Non‐Fluorinated Ionic Liquids

“…Therefore, investigations of the topmost layers of IL mixtures are getting more into the focus of research. A variety of studies has been performed, using reactive‐atom scattering with laser‐induced fluorescence detection (RAS‐LIF), neutron scattering, small‐angle X‐ray scattering and X‐ray reflectivity, time of flight secondary ion mass spectrometry (TOF‐SIMS), Rutherford backscattering spectroscopy (RBS), low‐energy ion scattering (LEIS), X‐ray photoelectron spectroscopy (XPS) and molecular dynamics (MD) simulations …”

Surface Enrichment in Equimolar Mixtures of Non‐Functionalized and Functionalized Imidazolium‐Based Ionic Liquids

“…The surface composition of binary IL mixtures with non‐functionalized imidazolium‐based ILs was investigated using various surface science techniques such as time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS),21,22 low‐energy ion scattering (LEIS),23,24 Rutherford backscattering (RBS),22,25, 26, 27 angle‐resolved X‐ray photoelectron spectroscopy (ARXPS),28, 29, 30 reactive atom scattering‐laser‐induced fluorescence (RAS‐LIF),20,31 and by simulations 20,26,32,33…”