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Scientific Unit
Single layer graphene induces load-bearing molecular layering at the hexadecane-steel interface
(2019)
The influence of a single layer graphene on the interface between a polished steel surface and the model lubricant hexadecane is explored by high-resolution force microscopy. Nanometer-scale friction is reduced by a factor of three on graphene compared to the steel substrate, with an ordered layer of hexadecane adsorbed on the graphene. Graphene furthermore induces a molecular ordering in the confined lubricant with an average range of 4–5 layers and with a strongly increased load-bearing capacity compared to the lubricant on the bare steel substrate.
Fingertip friction and the related shear of skin are key mechanical mechanisms in tactile perception, but the perception of friction itself is rarely explored except for the flat surfaces of tactile displays. We investigated the perception of friction for tactile exploaration of a unique set of samples whose fabric-like surfaces are equpped with regular arrays of flexible micropillars.The measured fingertip friction increases with decreasing bending stiffness, where the latter is controlled by radius (20-75 µm) an aspect ration of the micropillars. In forced-choice tasks, participants noticed relative differences in friction as small as 0.2, and even smaller when a sample with less than 100µm distance between pillars is omitted from the analysis. In an affective ranking of sample upon active touch, the perception of pleasantness is anticorrelated with the measured friction. Our results offer insights towards a rational design of materials with well-controlled surface microstructure which elicit a dedicated tactile appeal.
