Influence of electric potentials on friction of sliding contacts lubricated by an ionic liquid

Dold, Christian; Amann, Tobias; Kailer, Andreas

doi:10.1039/c4cp05965d

Cited by 38 publications

(41 citation statements)

References 41 publications

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“…Then it may prove to be important to prefer hydrophobic RTILs in order to take full advantage of such a mechanical response. Furthermore, future work may also explore the capabilities of RTILs as active lubricant, via the control of interfacial properties thanks to surface electric polarization [18,[37][38][39] The ionic liquid used is BmimBF4 and presents a typical ion pair size l ≈ 0.8 nm. This liquid exhibits a viscosity around 100 mPa s at room temperature [23] and a bulk freezing temperature T B ¼ −71°C [16].…”

Section: Discussionmentioning

confidence: 99%

Nanotribology of Ionic Liquids: Transition to Yielding Response in Nanometric Confinement with Metallic Surfaces

et al. 2020

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Room-temperature ionic liquids (RTILs) are molten salts which exhibit unique physical and chemical properties, commonly harnessed for lubrication and energy applications. The pure ionic nature of RTIL leads to strong electrostatic interactions among the liquid, furthermore exalted in the presence of interfaces and confinement. In this work, we use a tuning-fork-based dynamic surface force tribometer, which allows probing both the rheological and the tribological properties of RTIL films confined between a millimetric sphere and a surface, over a wide range of confinements. When the RTIL is confined between metallic surfaces, we see evidence of an abrupt change of its rheological properties below a threshold confinement. This is reminiscent of a recently reported confinement-induced capillary freezing, here observed with a wide contact area. In parallel, we probe the tribological response of the film under imposed nanometric shear deformation and unveil a yielding behavior of the interfacial solid phase below this threshold confinement. This is characterized by a transition from an elastic to a plastic regime, exhibiting striking similarities with the response of glassy materials. This transition to yielding of the RTIL in metallic confinement leads overall to a reduction in friction and offers a self-healing protection of the surfaces avoiding direct contact, with obvious applications in tribology.

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Section: Discussionmentioning

confidence: 99%

Nanotribology of Ionic Liquids: Transition to Yielding Response in Nanometric Confinement with Metallic Surfaces

et al. 2020

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“…However, a similarly strong friction drop occurred at positive bias upon sliding a sharp AFM tip on highly oriented pyrolytic graphite immersed in a [HM Im]F AP IL [9]. This diversity of behavior, reflecting the variety of ILs and the different nature of the confining and sliding sur-arXiv:1508.04801v1 [cond-mat.mtrl-sci] 19 Aug 2015 faces, suggests some flexibility in the corresponding theoretical modeling, aimed at a broad exploration of how some of this variety of behavior could be addressed with a handful of model parameters, rather than describing in details one or another particular case. The minimal IL model and a natural first choice is a simple molten salt, such as liquid NaCl.…”

Section: Introductionmentioning

confidence: 99%

Electrical charging effects on the sliding friction of a model nano-confined ionic liquid

Capozza

Benassi

Vanossi

et al. 2015

The Journal of Chemical Physics

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Recent measurements suggest the possibility to exploit ionic liquids (ILs) as smart lubricants for nano-contacts, tuning their tribological and rheological properties by charging the sliding interfaces. Following our earlier theoretical study of charging effects on nanoscale confinement and squeezout of a model IL, we present here molecular dynamics simulations of the frictional and lubrication properties of that model under charging conditions. First, we describe the case when two equally charged plates slide while being held together to a confinement distance of a few molecular layers. The shear sliding stress is found to rise strongly and discontinuously as the number of IL layers decreases stepwise. However, the shear stress shows, within each given number of layers, only a weak dependence upon the precise value of the normal load, a result in agreement with data extracted from recent experiments. We subsequently describe the case of opposite charging of the sliding plates and follow the shear stress when the charging is slowly and adiabatically reversed in the course of time, under fixed load. Despite the fixed load, the number and structure of the confined IL layers change with changing charge, and that in turn drives strong friction variations. The latter involves first of all charging-induced freezing of the IL film, followed by a discharging-induced melting, both made possible by the nanoscale confinement. Another mechanism for charging-induced frictional changes is a shift of the plane of maximum shear from mid-film to the plate-film interface, and vice versa. While these occurrences and results invariably depend upon the parameters of the model IL and upon its specific interaction with the plates, the present study helps identifying a variety of possible behavior, obtained under very simple assumptions, while connecting it to an underlying equilibrium thermodynamics picture.

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“…In a chloride environment for example there is a rapid passive film breakdown due to hydrolysis [48,49]. Recently published own work using ILs [50], aqueous solutions of ILs [51], and sodium chloride [52,53], we showed how strongly electrochemical potentials, applied in a three-electrode configuration [54], can improve friction, wear, and reduce tribocorrosive reactions. The Effect of potential in tribocorrosion of passive materials such as stainless steel has been previously studied and some degradation mechanisms have been already proposed [55,56].…”

Section: Introductionmentioning

confidence: 94%

Galvanically induced potentials to enable minimal tribochemical wear of stainless steel lubricated with sodium chloride and ionic liquid aqueous solution

et al. 2018

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The effect of galvanically induced potentials on the friction and wear behavior of a 1RK91 stainless steel regarding to tribocorrosion was investigated using an oscillating ball-on-disk tribometer equipped with an electrochemical cell. The aim of this investigation is to develop a water-based lubricant. Therefore 1 molar sodium chloride (NaCl) and 1% 1-ethyl-3-methylimidazolium chloride [C 2 mim][Cl] water solutions were used. Tribological performance at two galvanically induced potentials was compared with the non-polarized state: cathodic potential-coupling with pure aluminum-and anodic potential-coupling with pure copper. Frictional and electrochemical response was recorded during the tests. In addition, wear morphology and chemical composition of the steel were analyzed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. The galvanically induced cathodic polarization of the stainless steel surface results in electrochemical corrosion protection and the formation of a tribolayer. Cations from the electrolyte (sodium Na + and 1-ethyl-3-methylimidazolium [C 2 mim] +) interact and adhere on the surface. These chemical interactions lead to considerably reduced wear using 1 NaCl (86%) and 1% 1-ethyl-3-methylimidazolium chloride [C 2 mim][Cl] (74%) compared to the nonpolarized system. In addition, mechanical and corrosive part of wear was identified using this electrochemical technique. Therefore this method describes a promising method to develop water-based lubricants for technical applications.

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Influence of electric potentials on friction of sliding contacts lubricated by an ionic liquid

Cited by 38 publications

References 41 publications

Nanotribology of Ionic Liquids: Transition to Yielding Response in Nanometric Confinement with Metallic Surfaces

Nanotribology of Ionic Liquids: Transition to Yielding Response in Nanometric Confinement with Metallic Surfaces

Electrical charging effects on the sliding friction of a model nano-confined ionic liquid

Galvanically induced potentials to enable minimal tribochemical wear of stainless steel lubricated with sodium chloride and ionic liquid aqueous solution

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