Control of friction is a widely recognized problem that covers a broad range of materials from medical implants, to engines, to micro- and nano-scaled machine technologies. A ubiquitous challenge in many of these applications is how to control the wear that occurs in sliding contacts, which are dominated by the interactions between nanoscaled surface asperities, where the high pressures and shear forces that are experienced can result in increased friction and ultimately lead to device failure. Obtaining an atomic/molecular scale understanding of the interactions and energy dissipation mechanisms in asperity-asperity contacts at such interfaces is paramount for the rational design of new materials or lubrication schemes. We have developed a model platform to investigate true nanoscaled asperity-asperity contacts using silica nanoparticles deposited on a Si support to form surfaces with asperities of controlled radius of curvature (ca. 5 � 20 nm), matching those found in most machined interfaces. Friction, adhesion and wear at these surfaces are then explored using AFM where the AFM tip, acting as a single mobile asperity, allows us to probe asperity-asperity contacts. Molecular adlayers on silica, such as self-assembled monolayers (SAMs) can dramatically reduce friction in such interfaces, however they can be easily damaged during impact and shear. A challenge with these molecular adlayers is that nanoscale surface roughness impacts both the formation and quality of the SAMs, as compared to those formed on atomically smooth surfaces, decreasing film stability. Using AFM, IR spectroscopy and MD simulations, we have explored how the interplay of high pressure, surface curvature and molecular forces come together to control friction at the atomic/molecular level in asperity-asperity silica contacts. New approaches for friction modification of interfaces, including the deposition of single and few-layer graphene and graphene-SAM composites have also been examined and will be described.

Tuning the frictional properties of surfaces with nanoscale roughness using SAMs and graphene-SAM composites

248th National Meeting (2014)

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