The Mechanical Characterization of Multi-Wall Carbon Nanotubes and Related Interfaces in Nanocomposites

This thesis primarily documents the development and application of a novel technique, which involves the usage of a silicon micro-mechanical device that operates in conjunction with a quantitative nanoindenter within an electron microscope, for the mechanical characterization of nanomaterials and interfaces in composites. The technique was used to conducted tensile tests on individual pristine, nitrogen doped and sidewall fluorinated multi-wall carbon nanotubes (MWNTs), which were found to exhibit varied load-bearing abilities and unique fracture modes. The technique was also used to perform single fiber pullout experiments to study the MWNT/polymer (epoxy) interface. Interfacial failure was found to occur in a brittle fashion, in a manner consistent with the predictions of continuum fracture mechanics models. Although an improvement in the interfacial adhesion was observed upon sidewall fluorination of the MWNT reinforcements, the results of the study essentially highlighted the weak nature of the forces that bind MWNTs to an epoxy matrix

Fracture toughness of the sidewall fluorinated carbon nanotube-epoxy interface

The effects ofﾠcarbon nanotubeﾠ(CNT)ﾠsidewall fluorination on theﾠinterfaceﾠtoughness of theﾠCNTﾠepoxyﾠinterfaceﾠhave been comprehensively investigated. Nanoscale quantitative single-CNT pull-out experiments have been conducted on individual fluorinatedﾠCNTsﾠembedded in an epoxy matrix,ﾠin situ, within aﾠscanning electron microscopeﾠ(SEM)ﾠusing an InSEMﾮﾠnanoindenter assisted micro-device. Equations that were derived using a continuum fracture mechanics model have been applied to compute theﾠinterfacialﾠfracture energy values for the system. Theﾠinterfacialﾠfracture energy values have also been independently computed by modeling the fluorinated graphene-epoxyﾠinterfaceﾠusingﾠmolecular dynamics simulationsﾠandﾠadhesionﾠmechanisms have been proposed

Micromechanical devices for materials characterization

The present disclosure describes micromechanical devices and methods for using such devices for characterizing a material's strength. The micromechanical devices include an anchor pad, a top shuttle platform, a nanoindenter in movable contact with the top shuttle platform and at least two sample stage shuttles. The nanoindenter applies a compression force to the top shuttle platform, and the at least two sample stage shuttles move apart in response to the compression force. Each of the at least two sample stage shuttles is connected to the top shuttle platform and to the anchor pad by at least one inclined beam. Methods for using the devices include connecting a sample between the at least two sample stage shuttles and applying a compression force to the top shuttle platform. Application of the compression force to the top shuttle platform results in a tensile force being applied to the sample. Measuring a tip displacement of the nanoindenter is correlated with the sample's strength. Illustrative materials that can be studied using the micromechanical devices include, for example, nanotubes, nanowires, nanorings, nanocomposites and protein fibrils