Influence of Waviness on the Elastic Properties of Aligned Carbon Nanotube Polymer Matrix Nanocomposites

TL;DR

This study uses advanced simulations to show that the waviness of aligned carbon nanotubes significantly reduces the elastic modulus of nanocomposites, explaining discrepancies between theory and experiment.

Contribution

It introduces a simulation framework that accounts for realistic waviness in CNTs, revealing its impact on the elastic properties of nanocomposites, which was previously underestimated.

Findings

Waviness causes orders of magnitude over-prediction in elastic modulus models.

Existing models neglect shear deformation and CNT morphology, leading to inaccuracies.

Simulation results align better with experimental data when waviness is included.

Abstract

The promise of enhanced performance has motivated the study of one dimensional nanomaterials, especially aligned carbon nanotubes (A-CNTs), for the reinforcement of polymeric materials. While early work has shown that CNTs have remarkable theoretical properties, more recent work on aligned CNT polymer matrix nanocomposites (A-PNCs) have reported mechanical properties that are orders of magnitude lower than those predicted by rule of mixtures. This large difference primarily originates from the morphology of the CNTs that reinforce the A-PNCs, which have significant local curvature commonly referred to as waviness, but are commonly modeled using the oversimplified straight column geometry. Here we used a simulation framework capable of analyzing 10$^{5}$ wavy CNTs with realistic stochastic morphologies to study the influence of waviness on the compliance contribution of wavy A-CNTs to the effective elastic modulus of A-PNCs, and show that waviness is responsible for the orders of magnitude \textit{over-prediction} of the A-PNC effective modulus by existing theoretical frameworks that both neglect the shear deformation mechanism and do not properly account for the CNT morphpology. Additional work to quantify the morphology of A-PNCs in three dimensions and simulate their full elastic constitutive relations is planned.