A relationship between the force curve measured by atomic force microscopy in an ionic liquid and its density distribution on a substrate

Amano, Ken-ichi; Yokota, Yasuyuki; Ichii, Takashi; Yoshida, Norio; Nishi, Naoya; Katakura, Seiji; Imanishi, Akihito; Fukui, Ken–ichi; Sakka, Tetsuo

doi:10.1039/c7cp06948k

Cited by 24 publications

(25 citation statements)

References 42 publications

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“…These jumps are strongly dependent on the charging of the system. In the case that the tip or surface is not charged, the measured thicknesses of the layers correspond to the dimension of the anion or cation, respectively, but when a charged surface is investigated with a charged tip, the observed jumps correlate with the dimension of an ion pair [81]. In this manner, detailed information about mechanical properties and the thicknesses of the interface layers of ionic liquids can be collected with sub-nN and sub-nm resolution.…”

Section: Principles Of Atomic Force Spectroscopymentioning

confidence: 99%

Atomic Force Spectroscopy on Ionic Liquids

2019

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Ionic liquids have become of significant relevance in chemistry, as they can serve as environmentally-friendly solvents, electrolytes, and lubricants with bespoke properties. In particular for electrochemical applications, an understanding of the interface structure between the ionic liquid and an electrified interface is needed to model and optimize the reactions taking place on the solid surface. As with ionic liquids, the interplay between electrostatic forces and steric effects leads to an intrinsic heterogeneity, as the structure of the ionic liquid above an electrified interface cannot be described by the classical electrical double layer model. Instead, a layered solvation layer is present with a structure that depends on the material combination of the ionic liquid and substrate. In order to experimentally monitor this structure, atomic force spectroscopy (AFS) has become the method of choice. By measuring the force acting on a sharp microfabricated tip while approaching the surface in an ionic liquid, it has become possible to map the solvation layers with sub-nanometer resolution. In this review, we provide an overview of the AFS studies on ionic liquids published in recent years that illustrate how the interface is formed and how it can be modified by applying electrical potential or by adding impurities and solvents.

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Section: Principles Of Atomic Force Spectroscopymentioning

confidence: 99%

Atomic Force Spectroscopy on Ionic Liquids

2019

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“…3,4 At the solid interface of ILs, the ionic multilayer structure has been revealed by an atomic force microscopy (AFM). [5][6][7][8] When the solid substrate is highly charged, the ionic multilayers consist of alternating layers of cations and anions as found by molecular dynamics (MD) simulations, 9,10 theories, 11,12 and X-ray reflectometry. 10,13 Using MD simulation, Ivaništšev et al showed 9,10 that the density oscillation of alternating layers increases as the electric double layer (EDL) is charged up, but a further charge up causes the attenuation of the oscillation.…”

Section: Introductionmentioning

confidence: 98%

Surface Structure of Quaternary Ammonium-Based Ionic Liquids Studied Using Molecular Dynamics Simulation: Effect of Switching the Length of Alkyl Chains

et al. 2019

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Electric double layer structure at the electrode interface has been studied by using molecular dynamics simulation on four quaternary ammonium-based ionic liquids (QaILs) to investigate the effect of switching the alkyl chain length of the Qa cation. These four QaILs are composed of a common anion, bis(trifluoromethanesulfonyl)amide (TFSA −) and different cations: butyltrimethylammonium (N + 1114 , k = 1), dibutyldimethylammonium (N + 1144 , k = 2), tributylmethylammonium (N + 1444 , k = 3), and tetrabutylammonium (N + 4444 , k = 4), where k represents the number of butyl chains. The difference in k affects the potential dependence for the composition of the first ionic layer and the orientation of butyl chains in the layer. For the case of k = 1, 2, 3, the butyl chains parallel to the interface increases as the potential becomes negative, but further negative potential results in the increase in perpendicular ones. In the case of k = 1, all the cations in the first ionic layer show the perpendicular orientation at the negative potentials, forming a honeycomb lattice consisting of only cations. On the other hand, in the case of k = 4, no change in orientation has been observed due to the geometrical restrictions. The difference in k also affects the differential capacitance. The potential dependence of differential capacitance shows bell shape for the smaller two (k = 1, 2) and camel shape for the larger two (k = 3, 4). The camel shape for larger IL cations agrees with the prediction from the mean-field lattice gas model and recent experimental results. The differential capacitance at negative potentials deviated to the values higher than the model prediction and the discrepancy becomes greater for smaller k. The results indicate that the potential dependence of ionic orientation significantly affects the differential capacitance. Even for k = 4, which does not show the orientational change, the discrepancy has been observed, indicating that not only the orientational change but also the densification of ions in the first ionic layer are the factors we should take into account beyond the lattice gas model.

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“…These multiple peaks can be attributed to the surfactant molecules solvated on the surface in a fluid-like micelle, where the observation mechanism of the oscillatory peaks seems to be similar to that of room-temperature ionic liquids. 45 In our previous study, we already reported the observation of solvation layers inside the micelle, 28 but only two layers were observed. This result demonstrated that FM-AFM has an advantage of acquiring the solvation measurement over SM-AFM.…”

Section: Resultsmentioning

confidence: 95%

“…liquids. 45 In our previous study, we already reported the observation of solvation layers inside the micelle, 28 but only two layers were observed. This result demonstrated that FM-AFM has an advantage of acquiring the solvation measurement over SM-AFM.…”

Section: Disruption Process Of Micellesmentioning

confidence: 95%