Artificial Muscle Based On Oriented Carbon Nanotube Fibers

Due to the large strain, low density and high mechanical strength, electrically actuated artificial muscles have become one of the hot directions in intelligent materials. It can be widely used in acoustical, optical and electrical fields. However, there remain many challenges for the current artificial materials. For instance, electronic electroactive polymers require high actuated voltage and show low strain, while ionic electroactive polymers exhibit a slow response and work only in electrolyte media. It becomes critically important to design novel artificial muscles with the combined excellent properties. Carbon nanotube (CNT) fiber may become one of the ideal candidates due to the unique one-dimensional structure and remarkable physical properties. This thesis has mainly developed aligned CNT fibers as a new family of artificial muscles.Aligned CNT fibers had been dry-spun from CNT arrays which were synthesized by a typical chemical vapor deposition process. Due to the aligned structure of CNTs, the fibers had well maintained the extraordinary physical properties of individual CNTs, e.g., mechanical strengths on the level of (102-103) MPa and electrical conductivity on the order of (102-103) S/cm. As there were a lot of voids among CNTs, a second phase such as poly(acrylic acid) was incorporated to produce composite fibers with further improved performances. For instance, the strength and conductivity had been increased by2.5and1.2times, respectively.The aligned and helically organized CNT fiber was discovered to convert electrical energy to contraction and torsional mechanical energy. A large contraction strain of2%, high contraction stress of10MPa and high torsional strain of720°had been achieved at a low voltage of5V/cm. In addition, this artificial muscle also exhibited the other excellent properties such as a rapid response (0.2s), high tensile strength (0.8GPa), high conductivity (400S/cm) and low density (0.54g/cm3). The actuation had been produced by directly passing the current along them, without the use of a relatively complex three-electrode electromechanical setup. Ampere’s Law among helically aligned CNTs, explains the simultaneous occurrence of lengthwise contraction and rotary torsion upon applying a low current. The electromechanical torsion of CNT fiber occurred in almost all available environmental media such as air, water, and organic solvents besides electrolytes. The combined excellent properties provide the CNT fiber actuator with promising applications in many fields. The use of torsional fibers for electric motors and rapid release vehicles had been studied as two demonstrations.In summary, as the lengthwise contraction and rotary torsion can occur in almost all available media, this spun CNT fiber may represent a novel artificial muscle material for various fields, particularly, optoelectronc and sensing devices.