It is well-known that the fluid-like cushioning layer of solvated polymer brushes effectively reduces friction. The lubrication mechanism relies on the repulsive force of osmotic and steric origin that efficiently separates the two counter-surfaces, thereby hindering polymer chain overlap. As a consequence, a thin film of solvent remains between the two polymer chains providing a plane that is easy to shear, which reduces friction. To fully leverage the lubricating behavior of polymer brushes, a very good solvent is needed to stretch the anchored polymer chains. Ionic liquids (ILs) are considered outstanding solvents, and thus, they could potentially serve as the swelling agent for neutral polymers, and polyelectrolytes. Moreover, they have a low vapor pressure, high viscosity and thermal stability, and higher conductivity and electrochemical stability than other aqueous and non-aqueous solvents, which provides a route to design novel lubricant systems with improved properties for a greater field of applications.<br/>Ionic liquids are known to absorb on many surfaces and to form multi-layer boundary films at the solid-liquid interface. In the absence of tribochemistry, this behavior has been shown to promote low friction compared to lubricant oils under similar conditions. However, thermal fluctuations at soft interfaces, like in case of polymer brushes, are known to disturb the layering of boundary films, and hence, different mechanisms are responsible for the lubrication provided by these films. Based on our studies at the molecular scale, we propose various mechanisms underlying the shear behavior of binary systems composed of polymer films and ionic liquids.

Molecular insight into polymer-ionic liquid mediated lubrication

254th National Meeting (2017)

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