The Inherent Thermal Effect of Substrates on the Growth of Ultralong Carbon Nanotubes

Abstract

Ultralong carbon nanotubes (CNTs) are believed to be ideal candidates for various high-end applications because of their macroscale lengths, perfect structures, and excellent mechanical and electrical properties. The key to the wide application of ultralong CNTs is their controlled synthesis and mass production. Ultralong CNTs usually follow a flying kite-like growth mechanism, during which process there exists a thermal buoyancy that keeps ultralong CNTs floating in the gas flow. However, it remains vague for a long time about the origin of this thermal buoyancy. Herein, a simple and quantitative heat balance model is proposed to describe the inherent thermal effect of substrates, which explains the origin of the temperature difference between the substrate and the gas flow. The inherent thermal effect is found to be positively correlated with the emissivity of the substrates. Then, the local temperature gradient induced by the inherent thermal effect is found to result in both natural convection and thermophoresis. Thermophoretic force is proven to be the dominant driving force for lifting the ultralong CNTs up from the substrates. By utilizing the inherent thermal effect and designing the local temperature distribution, the areal density and orientation of ultralong CNT arrays are modulated.

High-Performance Airflow Sensors Based on Suspended Ultralong Carbon Nanotube Crossed Networks

“…First, ultralong CNTs, following the flying kite-like growth mechanism, were grown in the first direction via SIDS and they formed suspended CNT noncrossed networks (SCNT-nCNs) over the hole (Figure S2). Then, the substrate was rotated 90° and used for the growth of ultralong CNTs in another direction, resulting in the formation of SCNT-CNs under the self-assembling effect of strong van der Waals forces between two layers of ultralong CNTs. We also performed the smoke-assisted optical visualization to realize the direct observation of SCNT-CNs under optical microscopes .…”

Fluidization and Application of Carbon Nano Agglomerations

“…Reproduced with permission. [ 119 ] Copyright 2022, Wiley‐VCH. b) Schematic illustration of the in situ fabrication of CNT bundles by the GFF method.…”

“…To understand the structural control issues in HACNTs, it is imperative first to analyze their growth process. HACNTs, [119] Copyright 2022, Wiley-VCH. b) Schematic illustration of the in situ fabrication of CNT bundles by the GFF method.…”

“…[118] Under the combined influence of airflow drag, viscosity, gravity, and thermal buoyancy, HACNTs exist in a floating state (Figure 8a). [119] With vapor-assisted growth conditions, HACNTs can quickly reach decimeter-level lengths and achieve an ultrafast growth rate of 80-90 μm s −1 . [120,121] Because the gas-solid two-phase reaction experienced by HACNTs is based on horizontal flow, the force differs from that of the vertically aligned CNTs in the vertically fluidized bed.…”

“…Figure 8. a) Schematic illustration of the kite-flying growth mechanism of ULCNTs. Reproduced with permission [119]. Copyright 2022, Wiley-VCH.…”