Measurement of Maximum Static Frictional Force Using Vertically-Aligned Carbon Nanotubes

Abstract

According to the law of friction, the maximum static frictional force is proportional to the normal force. A carbon nanotube (CNT) is a nano-size, flexible material. Vertically-aligned (VA)-CNTs, growing with a high density and vertically to the substrate, can yield great friction force because of a large true contact area. To elucidate the property of nanoscale friction, we measured the VA-CNT's friction force. We used two types of VA-CNTs ; grown with Fe and Co as the catalysts. In the small normal force range, coefficient of static friction was higher than that in the bigger force range. This result is different from the law of friction indicating that coefficient of static friction force is constant. The Fe-catalyzed-CNTs yielded greater friction force than the Co-catalyzed-CNTs did. This can be explained by the morphology and crystallinity of those CNTs. Because the Fe-catalyzed-CNTs can contact the substrate surface closely, they can cause greater friction force.