Anisotropic interfacial friction of inclined multiwall carbon nanotube array surface

Anisotropic interfacial friction of an inclined, multiwalled carbon nanotube (MWCNT) array surface fabricated on a commercial electrostatic adsorption film substrate has been experimentally studied. As a typical case, the friction force of steel ball/inclined MWCNT along the inclined direction is 40% larger than that against the inclined direction. The significant interfacial friction anisotropy remains stable even after nearly 4000 sliding cycles. While the tilt of MWCNT close to the top surface layer significantly affected the interfacial friction, the underlying nanotubes only has limited effects. Based on the van der Waals interaction between the MWCNT and the steel ball, the achieved anisotropic interfacial friction at different sliding directions is quantitatively modeled and explained. The interplay between the lateral friction and normal adhesion force has also been found during the unloading process of friction test.