![]() ![]() In addition to the gas rectification effect, we found that a sterically constrained space inside the channel induced accelerated laminar flow with strong shear stress near the channel walls, resulting in the spontaneous condensation of floating CNTs along the direction of gas flow. Here we report an FCCVD method for the one-step fabrication of aligned CNT bundles using a gas rectifier (so-called honeycomb ceramic filters), which possesses one-dimensional straight channels for regulating the Reynolds number of a gaseous medium containing a growing CNT aerogel. Accordingly, a key challenge is to achieve flow-directed growth and alignment of CNTs simultaneously, in conjunction with use of the FCCVD method by controlling the fluid properties of the reaction gases. ![]() However the flow-directed growth of CNTs, known as the “kite-mechanism”, has been achieved using a flat surface with immobilized catalytic nanoparticles, maintaining large inter-tube distances to prevent entanglement through van der Waals attraction 27. To control the growth direction of CNTs, fluidics-based engineering plays an important role, such as in the growth of a straight CNT under laminar flow with a low Reynolds number and the growth of a wavy CNT under turbulent flow with a high Reynolds number 25, 26. Among the various synthesis methods of CNTs 20, 21, 22, 23, floating-catalyst chemical vapor deposition (FCCVD) enables the continuous and scalable production of a CNT aerogel (also referred to as an elastic smoke of CNTs) 10, 24. Therefore, a major challenge in developing macroscopic CNT fibers is currently focused on the use of post-processing techniques (dry spinning 9, 10, 11, 12, 13, wet spinning 14, 15, 16, combined dry–wet spinning 17, microcombing 18, and chemical crosslinking 19) to achieve uniaxial alignment and packing of CNTs.ĭespite extensive research on post-processing techniques, little is known about pre-processing techniques such as a direct route for the simultaneous production and alignment of CNT fibers. The structural entanglement incorporated in CNT fibers originates from the experimental difficulty in controlling the parallel alignment and hexagonal stacking of CNTs during the synthesis process. However, their macroscopic counterparts (e.g., assembly into fibers) demonstrate the properties far below than those expected for individual CNTs mainly due to the misorientation and low packing density of individual CNTs and/or CNT bundles, as well as the presence of defects and short length (typically on the order of micrometers) 7, 8. To this end, carbon nanotubes (CNTs), which possess unique cylindrical nanostructures connected with sp 2 C–C bonding, are promising candidates owing to their outstanding electrical 3, mechanical 4, 5, and thermal 6 properties at the nanoscale. ![]() There is an ever-increasing need for robust lightweight materials in a variety of fields on automotive, architectural, and aerospace applications 1, 2. FCCVD coupled with the strong shear stress of the reaction gas is an important pre-processing route for the fabrication of high-performance CNT fibers. The resulting CNT fiber exhibits a tensile strength of 2.1 ± 0.1 N tex −1 with a Young’s modulus of 39 ± 4 N tex −1 and an elongation of 6.3 ± 0.6%. After a wet-process using chlorosulfonic acid, the inter-tube voids inherently observed in as-grown CNT bundles are reduced from 16 to 0.3%. In addition, strong shear stress is induced near the side wall of the channels, resulting in the spontaneous formation of macroscopic CNT bundles aligned along the direction of the gas flow. Our computational fluid dynamics simulation reveals that the narrow channels of the gas rectifier provide steady and accelerated laminar flow of the reaction gas. The gas rectifier consists of one-dimensional straight channels for regulating the Reynolds number of the reaction gas. We report the one-step fabrication of aligned and high-quality carbon nanotubes (CNTs) using floating-catalyst chemical vapor deposition (FCCVD) with controlled fluidic properties assisted by a gas rectifier. ![]()
0 Comments
Leave a Reply. |