Molecularly-Thin Precursor Films of Imidazolium-Based Ionic Liquids on Mica

Beattie, David A.; Espinosa‐Marzal, Rosa M.; Ho, Tracey T. M.; Popescu, M. N.; Ralston, John; Richard, Céline J. E.; Sellapperumage, Pasindu M. F.; Krasowska, Marta

doi:10.1021/jp4062863

Cited by 49 publications

(51 citation statements)

References 82 publications

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“…This enable us to model both partial wetting and full wetting states. We recall that experiments with imidazolium salts and mica have reported both states [22][23][24] . Increasing the IL-surface interaction to ε ILS,2 induces 1) a shift in the maximum of the "volcano" curve towards lower surface charges, and 2) a significant increase in the friction at low surface charge density (see Figure 8).…”

Section: Dependence Of Friction With Surface Chargementioning

confidence: 92%

Electrotunable lubricity with ionic liquids: the influence of nanoscale roughness

et al. 2017

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The properties of ionic liquids can be modified by applying an external electrostatic potential, providing a route to control their performance in nanolubrication applications. Most computational studies to date have focused on the investigation of smooth surfaces. Real surfaces are generally inhomogeneous and feature roughness of different length scales. We report here a study of the possible effects that surface roughness may have on electrotunable lubricity with ionic liquids, performed here by means of non-equilibrium molecular dynamics simulations. In order to advance our understanding of the interplay of friction and substrate structure we investigate coarse grained models of ionic liquids confined in model surfaces with nanometer roughness. The friction is shown to depend on the roughness of the substrate and the direction of shear. For the investigated systems, the friction coefficient is found to increase with roughness. These results are in contrast with previous studies, where roughness induced reduction of friction was reported, and they highlight the strong sensitivity of the friction process to the structure of the surfaces. The friction force features a maximum at a specific surface charge density. This behaviour is reminiscent of the one reported in ionic liquids confined by flat surfaces, showing the generality of this physical effect in confined ionic liquids. We find that an increase of the substrate-liquid dispersion interactions shifts the maximum to lower surface charges. This effect opens a route to control electrotunable friction phenomena by tuning both the electrostatic potential and the composition of the confining surfaces.

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Section: Dependence Of Friction With Surface Chargementioning

confidence: 92%

Electrotunable lubricity with ionic liquids: the influence of nanoscale roughness

et al. 2017

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“…18,23 Squeezout phenomena and layering necessarily involve intimate features of the liquidsolid plate interface, not disconnected with those determining the plate wettability. Thus, it is important to monitor the plate wetting habit of our IL models.…”

Section: Wetting Propertiesmentioning

confidence: 99%

Squeezout phenomena and boundary layer formation of a model ionic liquid under confinement and charging

Capozza

Vanossi

Benassi

et al. 2015

The Journal of Chemical Physics

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Electrical charging of parallel plates confining a model ionic liquid down to nanoscale distances yields a variety of charge-induced changes in the structural features of the confined film. That includes even-odd switching of the structural layering and charging-induced solidification and melting, with important changes of local ordering between and within layers, and of squeezout behavior. By means of molecular dynamics simulations, we explore this variety of phenomena in the simplest charged Lennard-Jones coarse-grained model including or excluding the effect a neutral tail giving an anisotropic shape to one of the model ions. Using these models and open conditions permitting the flow of ions in and out of the interplate gap, we simulate the liquid squeezout to obtain the distance dependent structure and forces between the plates during their adiabatic approach under load. Simulations at fixed applied force illustrate an effective electrical pumping of the ionic liquid, from a thick nearly solid film that withstands the interplate pressure for high plate charge to complete squeezout following melting near zero charge. Effective enthalpy curves obtained by integration of interplate forces versus distance show the local minima that correspond to layering and predict the switching between one minimum and another under squeezing and charging.

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“…[27,[30][31][32][33] Due to their low vapor pressure, ILs are candidates for precursor film studies and the first study of precursor films spreading ahead of macroscopic droplets of imidazolium-based ILs (on smooth mica surfaces) was carriedo ut by Beattie et al [34] Additionally,i nr ecent literature reports there are several publications dedicated to interfacial tension studies, including the measuremento fc ontact anglesf ormed by various ILs on different solid substrates. [27,[30][31][32][33] Due to their low vapor pressure, ILs are candidates for precursor film studies and the first study of precursor films spreading ahead of macroscopic droplets of imidazolium-based ILs (on smooth mica surfaces) was carriedo ut by Beattie et al [34] Additionally,i nr ecent literature reports there are several publications dedicated to interfacial tension studies, including the measuremento fc ontact anglesf ormed by various ILs on different solid substrates.…”

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confidence: 99%

Morphology of Imidazolium‐Based Ionic Liquids as Deposited by Vapor Deposition: Micro‐/Nanodroplets and Thin Films

2016

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The morphology of micro-and nanodroplets and thin films of ionic liquids (ILs) prepared through physical vapor deposition is presented. The morphology of droplets deposited on indium-tin-oxide-coated glass is presented for the extended 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([CnC1im][Ntf2]; n= 1-8) series, and the results show the nano-structuration of ILs. The use of in-vacuum energetic particles enhances/increases the nanodroplets mobility/coalescence mechanisms and can be a pathway to the fabrication of thin IL films. Ionic liquids (ILs) are a family of materials that offer a range of properties that can be adjusted to optimize their performance in a diversity of technological applications. [1-3] ILs share common characteristics, such as ionic conductivity, good thermal stability, and extremely low vapor pressure at room temperature. [4-6] In recent years, extensive studies of the thermo-physical properties of ILs have shown that almost none of these properties are shared across the IL range due to structural/nanostructural modifications. [7-9] ILs are becoming particularly attractive for many applications, such as solvents for electro-chemistry (electrically conducting fluids, electrolytes), sealants, chemical industry, gas handling, pharmaceuticals, cellulose processing, dye-sensitized solar cells, waste recycling, batteries, dispersion of nanomaterials, and electrode-electrolyte interfaces in high-vacuum systems. [10-15] Recently, the liquid/vacuum and liquid/solid interfaces of ILs have been of great relevance for most of the above-mentioned applications, and model surface studies and molecular orientation/ordering investigations of ILs have been performed on surfaces with different chemical properties: Au, Ni, silica, graphene, alumina, glass, and mica. [16-20] In some cases, thin films of ILs have been prepared by using impregnation techniques with solutions of ILs in volatile solvents, followed by solvent removal by evaporation. Thus, nanostructures of ILs can be prepared by spin/dip-coating methods and the films have low thicknesses and exceptional lubrication characteristics. [20] In recent years, the focus has been on physical vapor deposition (PVD) of ILs on different surfaces [16, 18, 19]

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Molecularly-Thin Precursor Films of Imidazolium-Based Ionic Liquids on Mica

Cited by 49 publications

References 82 publications

Electrotunable lubricity with ionic liquids: the influence of nanoscale roughness

Electrotunable lubricity with ionic liquids: the influence of nanoscale roughness

Squeezout phenomena and boundary layer formation of a model ionic liquid under confinement and charging

Morphology of Imidazolium‐Based Ionic Liquids as Deposited by Vapor Deposition: Micro‐/Nanodroplets and Thin Films

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