Lowering of Friction in Monolayers of Mixed Alkanes
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Molecular structure and tribological properties of monolayers, formed by pure n-tetracosane (C24H50, hereafter C24), n-octatetracontane (C48H98, C48) and their binary mixture on highly oriented pyrolitic graphite (HOPG), were investigated by scanning tunneling microscopy (STM) and magnetic levitation tribometer (MLT) methods. It has been found that monolayers of pure C24 and C48 have typical smectic lamella-like packing with perpendicular orientation of molecules with respect to the lamella direction, while binary mixture C24 + C48 forms nematic phase with only orientational order. Comparative tribological MLT measurements reveal substantial lowering of friction coefficient μ for monolayers of C24 + C48 in contrast to pure C24 and C48. The lowering of friction is explained in terms of incommensurability between alkyl chain and graphite surface.
Keywordsn-Alkane Graphite Self-assembled monolayers Monolayer instability Sliding force Friction coefficient
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