Effect of Hydrogen Concentration on the Growth of Carbon Nanotube Arrays for Gecko-Inspired Adhesive Applications

Yang Li,Yali Duan,Keju Ji,Zhendong Dai,Guiyun Meng

doi:10.3390/coatings7120221

Yang Li, Yali Duan + Show 3 more

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https://doi.org/10.3390/coatings7120221

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Journal: Coatings	Publication Date: Dec 5, 2017
Citations: 20	License type: CC BY 4.0

Affiliation: Nanjing University of Aeronautics and Astronautics

Abstract

Vertically-aligned carbon nanotubes (VACNTs) have extraordinary structural and mechanical properties, and have been considered as potential candidates for creating dry adhesives inspired by adhesive structures in nature. Catalytic chemical vapor deposition is widely used to grow VACNTs; however, the influential mechanism of VACNT preparation parameters (such as H2 concentration) on its adhesion property is not clear, making accurate control over the structure of VACNTs adhesive an ongoing challenge. In this article, we use electron beam-deposited SiO2/Al2O3 as a support layer, Fe as catalyst, and C2H4/H2 gas mixtures as a feed gas to prepare VACNTs, while varying the ratio of the reducing atmosphere (H2) from 0% to 35%. VACNTs synthesized at a 15% H2 concentration (5 mm × 5 mm in size) can support a maximal weight of 856 g, which indicates a macroscopic shear adhesive strength of 34 N/cm2. We propose a hydrogen-concentration-dependent model for the shear adhesive performance of VACNTs. By adjusting the amount of hydrogen present during the reaction, the morphology and quality of the prepared VACNTs can be precisely controlled, which significantly influences its shear adhesive performance. These results are advantageous for the application of carbon nanotubes as dry adhesives.

Highlights

Geckos contain millions of microscopic beta keratin hairs on their feet, which allow them to exhibit controllable adhesion and detachment of their feet from a surface
The surface morphology of vertically-aligned carbon nanotubes (VACNTs) is very important for their application as dry adhesive materials
SEM images of VACNTs prepared under different hydrogen conditions are presented in Figure 1, and show typical side profiles and top surfaces of VACNTs

Summary

Introduction

Geckos contain millions of microscopic beta keratin hairs on their feet, which allow them to exhibit controllable adhesion and detachment of their feet from a surface The ends of these hairs are split into nanoscale spatula-like structures, which come in close contact with the target surface to induce accumulated van der Waals forces (~10 N/cm2 ) and form strong bonds [1,2]. This unique adhesive capability of geckos has led to the development of advanced adhesives, including dry adhesives, which unlike chemical adhesives, leave no residue [3].

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