Are Buckminsterfullerenes Molecular Ball Bearings?

Abstract

Buckminsterfullerenes (C 60) are near-spherical 2 molecules which freely rotate at room temper-3 ature in the solid state and when dissolved in 4 solution. An intriguing question arises as to 5 whether C 60 molecules can act as molecular 6 ball bearings, i.e. preventing direct contact 7 between two solid surfaces whilst simultane-8 ously dissipating shear stress through fast ro-9 tation. To explore this, we performed measure-10 ments of friction across a solution of C 60 in the 11 boundary lubrication regime. High resolution 12 shear and normal force measurements between 13 mica sheets separated by the C 60 solution were 14 made using a Surface Force Balance to provide a 15 single-asperity contact and sub-nanometer res-16 olution in lm thickness. We nd that, even 17 at small volume fraction, C 60 forms a solid-like 18 amorphous boundary lm sustaining high nor-19 mal load, suggesting that this system undergoes 20 a glass transition under connement. The C 60 21 lm gives rise to a low friction coecient up 22 to moderate applied loads, and we discuss the 23 possible relevance of the ball bearing eect at 24 the molecular scale. 25 2 Ball bearings, consisting of 40 balls running along a groove (e.g. in an axle 41 assembly), are designed to reduce the friction 42 further by transforming sliding into rolling. It 43

Friction of Ionic Liquid–Glycol Ether Mixtures at Titanium Interfaces: Negative Load Dependence

“…When the interlocking of those ion layers is strongly ordered, the resulted friction force could also be larger than the normal load. [30,31] We attribute larger friction forces observed in high IL concentration systems (75 wt% and 100 wt%) to the high viscosity. Because the main cause of friction in hydrodynamic/elastohydrodynamic regimes is hydrodynamic drag, which is proportional to the lubricant viscosity.…”

Nanolubrication in deep eutectic solvents

“…33 The formation of a robust, low friction surface film has lead to ionic liquids being proposed as a novel lubricant system. [34][35][36] In this work, we apply the surface force balance technique to the deep eutectic solvent ethaline, a 1 : 2 molar mixture of choline chloride and ethylene glycol. We report surface layering consistent with previous AFM measurements, [13][14][15] but with greater force resolution enabling the detection of weaker surface layers than previously reported, and anomalous longranged forces consistent with 'underscreening'.…”

The Influence of Mechanical Deformations on Surface Force Measurements

“…For these two reasons, the mechanical deformations of the confining surfaces are expected to influence the measured force profile also in the case of AFM. Irrespective of the particular system or technique used, it is very important to know the degree of convolution, i.e., whether the solid compression is negligible or dominant compared to the liquid compression, in order to interpret properly the structural force profile regarding the compressibility of the liquid layers [33,70,[75][76][77][78][79]. Indeed, this question of the "elasticity" of a thin liquid film is connected to a strong debate in the community, to understand how a liquid can exhibit a solid-like behaviour in nanoconfinement [8,[80][81][82][83].…”