19. Electrothermally Driven Carbon-Based Materials as EAPs: Fundamentals and Device Configurations

Inserting twist into carbon nanotube fibers has enabled novel actuation mechanisms that result in both rotating and linear translational movement. Heating the carbon nanotube fibers generates a volume increase that drives a partial untwist of the fiber. The process is reversible upon cooling with the aid of a return spring mechanism. The actuation can be magnified by incorporation of a guest material, such as paraffin wax. The torsional stroke and/or torque can be used to perform useful work, such as the rotation of an attached paddle for fluid mixing. Various device configurations are possible and can be modeled by torsion mechanics. Tensile contraction also occurs during fiber untwist and can be greatly magnified by overtwisting the yarns to form spring-like coils. The high conductivity of the carbon nanotube yarns facilitates the convenient electrical heating and control giving high stroke, long-life, and rapid tensile and torsional actuation. This chapter summarizes the methods to produce guest-filled carbon nanotube yarns and the configurations that can be employed to generate either torsional or tensile actuation.