Title: Experimental and analytical study of frictional anisotropy of nanotubes

The frictional properties of Carbon and Boron Nitride nanotubes (NTs) are very important in a variety of applications, including composite materials, carbon fibers, and micro/nano-electromechanical systems. Atomic force microscopy (AFM) is a powerful tool to investigate with nanoscale resolution the frictional properties of individual NTs.~Here, we report on an experimental study of the frictional properties of~different types of~supported~nanotubes~by AFM. We also~propose a~quantitative model to describe and then predict the frictional properties of nanotubes sliding on a substrate along (longitudinal friction) or perpendicular (transverse friction) their axis. This model provides a simple but general analytical relationship that well describes~the~acquired experimental~data.~As an example of potential applications, this~experimental method combined with the~proposed~model can guide to design better~NTs-ceramic composites, or to self-assemble the nanotubes on a surface in a given direction.