Mechanism of friction in rotating carbon nanotube bearings

Simulation of friction in carbon nanotube (CNT) bearing systems has been a popular topic, yet many questions remain open. For example, quantitative estimates of friction reported to date range by as much as eight orders of magnitude, and simulation techniques employ a variety of disparate simulation paradigms and parameters. This paper presents a new suite of consistently implemented but complementary and independent molecular simulations of rotary CNT bearing systems, which span the approaches reported to date, yet agree quantitatively within the error margin, or about one order of magnitude. A comparison between these new results, existing simulation results, and one experimental friction datum is presented. Furthermore, quantitative relationships between friction and the system operating parameters are determined. Friction is found to vary linearly with rotating speed and system temperature, while system length and mean diameter do not have a strong effect. Finally, based on phonon energy spectrum computations, we show that friction is a broadband phenomenon, which does not depend strongly on a specific vibrational mode, but rather appears to occur from the aggregate interactions of many modes at different frequencies. This work reports an in-depth analysis of the mechanics of CNT friction and shows that it can be simulated using complementary approaches, while still obtaining the same result. The analysis reveals the underlying mechanism causing friction and how the governing parameters affect its behavior. (C) 2012 Elsevier Ltd. All rights reserved.