Tuning Nanoscale Friction on Pt Nanoparticles with Engineering of Organic Capping Layer

Abstract

Nanoscale friction and adhesion on Pt colloid nanoparticles coated with different organic capping layers were probed with atomic/friction force microscopy. Platinum colloid nanoparticles with four types of capping layers have been synthesized and used as model lubricant systems: TTAB (tetradecyltrimethylammonium bromide), HDA (hexadecylamine), HDT (hexadecylthiol), and PVP (poly(vinylpyrrolidone)). Two-dimensional arrays of colloid nanoparticles were prepared using the Langmuir-Blodgett method. We found that the friction and adhesion properties on colloid nanoparticles are lower than those on a silicon surface. The variation of friction when changing the capping layers is similar to 30%, and it appears that the friction depends on the packing and ordering of the capping layers. Partial removal of the capping layers using ultraviolet light (UV)-ozone surface treatment resulted in increased friction. These results suggest a new method of tuning nanometer scale friction and adhesion by engineering organic capping layers on nanoparticles.