Evaluating the forces generated during carbon nanotube forest growth and self-assembly

Abstract

The time-resolved reaction forces generated by actively growing and interacting carbon nanotube (CNT) forests are investigated using a mechanical finite element model. The CNT–CNT interaction forces are transmitted to the CNT catalyst particle residing at the base of each CNT, which may alter catalyst kinetics and modulate CNT growth rate. The simulation shows that CNTs growing at a rate greater than the population average transmit compressive force to the catalyst particle, while those growing at a slower rate transmitted tensile force. The magnitude of force for CNTs growing at a rate that was +/− 10% of the population average was on the order of 100′s of nanonewtons, corresponding to stress on the order of GPa. When using an Arrhenius-like kinetic model to modulate CNT growth rates, the growth rate of slower CNTs was enhanced by tensile forces, while the growth rate of faster growing CNTs was decreased by compressive forces. The net result of the force-modulation kinetics was a reaction force reduction of approximately an order of magnitude. Understanding how the growth parameters of an individual CNT are related to the mechanical forces it experiences during CNT forest assembly and the overall CNT morphology is expected to improve the control of CNT forest morphology and ensemble forest properties.