Mechanisms of Single-Walled Carbon Nanotube Network Formation and Its Configuration in Polymer-Based Nanocomposites

Alen Oseli,Lidija Slemenik Perše,Ema Žagar,Alenka Vesel

doi:10.1021/acs.macromol.0c02763

Abstract

The reinforcing and conductive performance of carbon nanotube polymer-based nanocomposites depends on the established network and its configuration. Within this study, we report on the underlying mechanisms of such network formation utilizing single-walled carbon nanotubes (SWCNTs) in low- and high-density polyethylene matrices. Mechanisms were theoretically evaluated through Doi–Edwards theory and experimentally confirmed through plasma etching coupled with electron microscopy as well as rheological flow tests. Results showed that the established network is constructed from SWCNT bundles, which geometrically entangle at a critical volume fraction Φv,crit (number of rods: β ≈ 30). Below Φv,crit, the bundles behave as individual units and may align in the flow direction. Above Φv,crit, the rotation of bundles is constrained by neighboring units, leading to a random network configuration. Moreover, the theory successfully explains SWCNT bundle behavior as a Brownian entity and predicts network formation through diminishing thermo- and hydro-dynamically driven diffusion, which can be manipulated during the production to enhance reinforcing/conductive functionality of such materials.

Highlights

The anisotropic nature allows carbon nanotubes (CNTs) to establish a randomly connected web in polymer matrices, which can be utilized as mechanical reinforcement or a conducting pathway in numerous present and future emerging technologies, from multi-functional structural elements to flexible electronic devices, sensors, and so forth.[1,2] the functional performance of CNT−polymer nanocomposites primarily depends on the established network and its configuration driven by nanofiller geometry, content, and various mechanisms during nanocomposite production
scanning electron microscopy (SEM) micrographs were obtained on plasma-etched LDPE and HDPE nanocomposites, which revealed the single-walled carbon nanotubes (SWCNTs) network and its properties
The results showed that the Doi−Edwards theory successfully explains SWCNT bundle behavior as stiff rodlike particles in high-viscosity systems and predicts subsequent network formation, its configuration, and growth through diminishing thermo- and hydro-dynamically driven diffusion

Summary

Introduction

The anisotropic nature allows carbon nanotubes (CNTs) to establish a randomly connected web (network) in polymer matrices, which can be utilized as mechanical reinforcement or a conducting pathway in numerous present and future emerging technologies, from multi-functional structural elements to flexible electronic devices, sensors, and so forth.[1,2] the functional performance of CNT−polymer nanocomposites primarily depends on the established network and its configuration (dispersed high reinforcement and aggregated high conductivity) driven by nanofiller geometry, content, and various mechanisms during nanocomposite production (rupture, erosion, diffusion, clustering, etc.). For the ideal rod-like particle systems suspended in a medium, the establishment of the network is usually associated with geometrical entanglements of such particles known as geometrical percolation threshold, either observed through rheological (rheological threshold) or to a certain extent electrical (electrical threshold) measurements.[3,4] At low particle content (below geometrical percolation) in dilute regime, such anisotropic particles can rotate freely about their center mass, mainly acting on the surrounding medium, where no particle−particle interactions are observed. By increasing the particle content (above the percolation threshold), in a semi-dilute regime, particles establish a randomly connected web. Within this region, particle movement is severely constrained by the adjacent particles.

Methods

Results

Conclusion