Frictional Properties of Carbon Nanotube Films with a Load Range from Micronewton to Millinewton Using mm Size Balls

Abstract

Tribological properties of a vertically aligned carbon nanotube (CNT) film with a thickness of approximately 700 μm under millinewton and micronewton level loads were investigated using a 1 mm radius ball. At the beginning of frictional slidings, friction forces were high, and then decreased and seemed to reach relative steady state values, in both millinewton and micronewton load experiments. After the initial high frictions, top surface CNTs contacting with the counterpart ball on the CNT film were plastically deformed and bundled each other, which were observed to be flat by scanning electron microscopy (SEM). In the relative steady friction states, the friction forces basically increased with increasing loads. Under millinewton level loads, curves of the friction force as a function of the loads seemed to be parabolic. Surprisingly, although no adhesion forces were detected, frictions existed even at zero loads under micronewton loads.