Effect of structural transitions of n-hexadecane in nanoscale confinement on atomic friction

Load‐Dependent Friction Hysteresis for Graphitic Surfaces in n‐Hexadecane

“…The molecular organization of liquids in the vicinity of a surface impacts several interfacial phenomena, including adsorption, electrochemical, transport, and friction properties. [1][2][3][4][5] The complexity of the structural arrangement of liquids is further enhanced in the presence of a 2D material. [1,2,6,7] Graphene, the 2D form of graphite, shows tremendous promise as the nextgeneration additive in liquid-based lubrication, especially when suspended in solvents such as water, [4,8] oils, [1] or ionic liquids.…”

“…[1][2][3][4][5] The complexity of the structural arrangement of liquids is further enhanced in the presence of a 2D material. [1,2,6,7] Graphene, the 2D form of graphite, shows tremendous promise as the nextgeneration additive in liquid-based lubrication, especially when suspended in solvents such as water, [4,8] oils, [1] or ionic liquids. [4,9] Initial studies have shown that solvent structuring on the substrate-supported 2D layer(s) has a direct impact on friction.…”

“…[4,9] Initial studies have shown that solvent structuring on the substrate-supported 2D layer(s) has a direct impact on friction. [1,8,10] Solvent structuring can also impact other complex friction interlayer binding (exfoliation) energy of graphite. A friction hysteresis with a negative coefficient of friction during unloading was observed when surface layers from the bulk separate locally (and reversibly), leading to energy loss associated with the displacement of the deformed region.…”

“…[26,27] Further, when sheared, the confined hexadecane layers closest to the interface displayed increased shear viscosity by at least two to three times than the bulk [28] and enhanced molecular ordering of alkanes with the sliding history [29] or at the vicinity of defects, [30] etc. The non-DLVO (Derjaguin, Landau, Verwey, and Overbeek) oscillatory force profiles (solvation forces) measured on graphite, [1,2,4,31] show structural commensurability of alkanes with the graphitic surface, leading to their preferential adsorption. In addition, the high dispersive interactions among alkane chains and between alkane-hydrophobic graphitic surfaces lead to a highly packed, parallel-lying configuration of n-hexadecane molecules at the surface.…”

“…[8,9] A similar structural layering of alkanes was observed on supported graphene, and the molecular packing was shown to be highly susceptible to the flexibility of graphene (upon liquid intercalation), affecting the shear forces. [1,2] In this paper, systematic load-dependent friction measurements are conducted on HOPG and supported FL-graphene immersed in the n-hexadecane solution using AFM and molecular dynamics (MD) simulations. Adhesion, solvation layering, and atomic length scale friction loops were measured using AFM as a function of loading history.…”