Measurement of Flexural Rigidity of Multi-Walled Carbon Nanotubes by Dynamic Scanning Electron Microscopy

Renata Fortini,Dominic Kehren,Ulrich Gernert,Heinz Sturm,Asmus Meyer-Plath,Leonardo Agudo Jácome

doi:10.3390/fib8050031

Abstract

In this work the flexural rigidity of individual large diameter multi-walled carbon nanotubes (MWCNTs) was investigated. The bending modulus were obtained by detecting the resonance frequencies of mechanically excited cantilevered carbon nanotubes using the so-called dynamic scanning electron microscopy technique, and applying the Euler–Bernoulli beam theory. For the nanotubes studied, we determined a modulus of up to 160 GPa. This agrees with values reported by other authors for MWCNTs produced by catalytic chemical vapor deposition, however, it is 6-8 times smaller than values reported for single and multi-walled carbon nanotubes produced by arc-discharge synthesis. Toxicological studies with carbon nanotubes have been showing that inhaled airborne nanofibers that reach the deep airways of the respiratory system may lead to serious, asbestos-like lung diseases. These studies suggested that their toxicity critically depends on the fiber flexural rigidity, with high rigidity causing cell lesions. To complement the correlation between observed toxicological effects and fiber rigidities, reliable and routinely applicable measurement techniques for the flexural rigidity of nanofibers are required.

Highlights

Carbon nanotubes (CNTs) are materials that, depending on the structural order and degree of functionalization, may combine a number of exceptional properties including low material density, high chemical inertness, high electrical and thermal conductivity as well as very high tensile strength.These properties, some of them superior even to that of steel, have initiated a broad spectrum of fundamental materials research as well as application development activities
Lower bending modulus values were observed for multi-walled carbon nanotubes (MWCNTs) synthesized by chemical vapor deposition (cCVD) tested with atomic force microscopy, SEM and laser Doppler vibrometry
The nanotubes studied in this work exhibited bending modulus from 15 to 161 GPa, which are in the range of bending modulus values reported by other authors for MWCNTs synthesized by cCVD

Summary

Introduction

Carbon nanotubes (CNTs) are materials that, depending on the structural order and degree of functionalization, may combine a number of exceptional properties including low material density, high chemical inertness, high electrical and thermal conductivity as well as very high tensile strength. These properties, some of them superior even to that of steel, have initiated a broad spectrum of fundamental materials research as well as application development activities. Catalytic CVD is the most-frequently applied method for large-scale manufacturing of CNTs [1,2]. During CNT synthesis and handling, initial processes like product collection and reactor cleaning, as well as secondary processes like CNT powder milling and mixing, product

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