Control of friction and wear is a ubiquitous challenge in numerous machined interfaces ranging from biomedical implants, to engines, to nano- and micro-scaled electromechanical systems (MEMS) devices. Central to developing boundary lubrication schemes for such applications is how to reduce wear at the rough surfaces of such surfaces, where nanoscaled asperities dominate the interfacial contacts that can lead to wear. The robust mechanical properties and general chemical inertness of two-dimensional (2D) nanomaterials, such as graphene and MoS2, has made them of interest as friction modifiers. While single layer graphene and MoS2 can readily adapt to surface structure on the atomic scale, when deposited on substrates with nanoscopic roughness of ~ 10 nm rms (as is common in many machined interfaces) a conformal coating generally cannot be fully formed, due to competition between adhesion to the substrate nanoscopic asperities and the bending rigidity of the material. This often leaves a mixture of supported and unsupported regions which respond differently to applied load, with spatial variations in mechanical properties and chemical bonding. Increased strain in these materials on rough surfaces has also been seen to increase their chemical reactivity. Here, we describe a combination of AFM nanomechanical, confocal Raman microspectroscopic and near field IR scattering studies of graphene and MoS2 on silica surfaces with controlled nanoscopic roughness, to examine the how this impacts their frictional properties, and alters their electronic properties and chemical reactivity, where strain dependent reactions can be driven by applied forces. Studies of MoS2 on metal surfaces, such as Au(111) will also be described, where even within single layer MoS2, varying phases of the MoS2 are found to occur.

Friction and mechanochemical reactivity of 2D nanomaterials

2019 Fall National Meeting

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