Research paper of the month
October 2014 - Electric Field-Modulated Non-Ohmic Behavior of Carbon Nanotube Fibers in Polar Liquids
We describe a, previously unseen, electro-structural phenomenon in carbon nanotube (CNT) fibres, produced in the Department by a direct spinning process, which may find applications in future sensing and actuation technologies. When immersed in penetrating polar liquids, the fibres' electrical resistance is modulated by the applied probe current in a direct-current four point circuit: decreasing at higher currents and increasing at lower ones. The change in resistance is non-instantaneous and the rate of change correlates with the viscosity of the immersion medium. Supported by synchrotron small-angle x-ray scattering and impedance spectroscopy, we propose a model in which the gap distance, and thus the conductance, of capacitive junctions between CNT bundles is controlled by the applied electric field. This non-ohmic behaviour is ultimately a manifestation of nanoscale effects detectable on a macroscopic length scale. Although CNT fibres are the first example known to us where such behaviour is due to changes in structure on meso- and nanoscales, we anticipate that our results will apply to a variety of emerging hierarchical structures made up of other nano-building blocks assembled into macroscopic materials, such as graphene fibres, nanowire membranes, and various other macroscopic hybrid materials.
Figure: Graphical abstract as published in ACS Nano. The open junctions between nanotube bundles in the CNT network behave as leaky capacitors. The applied electric field pulls the bundles closer together and improves the conductivity of the fibres.
Jeronimo Terrones, James A. Elliott, Juan J. Vilatela, and Alan H. Windle, "Electric Field-Modulated Non-ohmic Behavior of Carbon Nanotube Fibers in Polar Liquids", ACS Nano, Article ASAP (2014).