Controlled Synthesis Of Carbon Nanotubes And Their Application For Artificial Muscles

Carbon nanotubes can be seen as one-dimensional, hollow, cylindrical structures formed by coaxial layers of graphene. The layers are called walls. Based on the number of walls, carbon nanotubes can be divided into single-walled carbon nanotubes and multi-walled carbon nanotubes. Carbon nanotubes have excellent electronic, mechanical, thermal, optical, chemical and electrochemical properties, which enable great potential applications in many related areas. However, there are still some problems that limit their practical application. One of the main problems for single-walled carbon nanotubes is the mixed growth of semiconducting and metallic species, which greatly inhibits their use as high performance electronics. Another specific issue is in the field of artificial muscles. Carbon nanotubes have numerous fundamentally different uses in artificial muscles, however, together with other current techniques in this area, there exist a lot of major limitations, including slow response, low work capacity, short cycle life, huge hysteresis, a reliance on electrolytes, and/or a narrow temperature range for operation. In order to solve these above mentioned problems and help promote the practical application of carbon nanotubes, we have explored the following studies:1. Synthesis of semiconducting SWNTs by arc discharge and their enhancement of water splitting performance with TiO2photocatalyst. A feasible and scalable CO2-assisted arc discharge method was developed to directly synthesize single-walled carbon nanotubes (SWNTs) with largely semiconducting species. Not only was electronic-type selectivity achieved on a large scale, with a semiconducting SWNT (s-SWNT) content of>90%, but also diameter selectivity was obtained, with a majority having diameters of>1.5nm. The photo-catalytic water splitting performance of these SWNTs with different ratios of s-SWNTs to metallic single-walled carbon nanotubes (m-SWNTs) was examined. The results show that, compared with m-SWNTs, s-SWNTs demonstrate a much better photocatalytic effect when used together with the common photo-catalyst TiO2. 2. Electrically, chemically, and photonically powered torsional and tensile actuation of hybrid carbon nanotube yarn muscles. Artificial muscles are of practical interest, but few types have been commercially exploited. Typical problems include slow response, low strain and force generation, short cycle life, use of electrolytes, and low energy efficiency. We have designed guest-filled, twist-spun carbon nanotube yarns as electrolyte-free muscles that provide fast, high-force, large-stroke torsional and tensile actuation. More than a million torsional and tensile actuation cycles are demonstrated, wherein a muscle spins a rotor at an average11,500revolutions/minute or delivers3%tensile contraction at1200cycles/minute. Electrical, chemical, or photonic excitation of hybrid yarns changes guest dimensions and generates torsional rotation and contraction of the yarn host. Demonstrations include torsional motors, contractile muscles, and sensors that capture the energy of the sensing process to mechanically actuate.