Nanotube actuators for nanomechanics

Carbon nanotubes are unique nanostructures with interesting properties that suit them to a range of diverse applications including nanoscale electronics, use in composites, as gas storage media and scanning probe tips. An exciting property of carbon nanotubes is their ability to efficiently convert electrical energy into mechanical energy (actuation). Nanotube actuation is caused by the geometrical expansion of the carbon–carbon covalent bond caused by charge transfer into the nanotube [Abstract American Chemical Society 22 (1999); Abstract American Chemical Society 20 (2000)]. This ability to actuate, in addition to their high strength (∼1 TPa), makes macro-scale sheets of nanotubes termed `bucky paperʹ, ideal for artificial muscles [Science 284 (1999) 1340]. Carbon nanotube actuators based on bucky paper have been shown to generate an order of magnitude higher stresses than those observed for natural muscle. These promising results suggest that carbon nanotube actuators based on a single (or a few hundred) nanotubes will also lead to enhanced applications on the micro- or nano-scale in the biomedical or electronic fields. This paper provides an overview of carbon nanotube actuators, their exceptional properties, current research ideas and possibilities for future applications.