From Collisions to Bundles: An Adaptive Coarse-Grained Model for the Aggregation of High-Aspect-Ratio Carbon Nanotubes

Abstract

We present an adaptive mesoscale model for carbon nanotube (CNT) systems. In our model, CNTs are represented as a chain of nodes connected by tensile and torsion springs to describe stretching and bending of the chain with intermolecular interactions being calculated using a mesoscopic Lennard-Jones potential. Computational adaptivity was achieved by dynamically adjusting node spacing and number during the simulation to optimise the number of simulated particles and lower computational effort. Adaptive simulations were up to five times faster than non-adaptive ones whilst quantitatively preserving all system dynamics. In particular, the model enables the study of the timescale of CNT bundling that leads to the formation of dilute CNT networks, so-called aerogels. These aerogels constitute the first step in the direct spinning of CNT fibres from chemical vapour deposition synthesis. Understanding the factors governing CNT bundling and network formation is key to controlling CNT fibre microstructure, and therefore optimising their properties. Using the model, we simulated the bundling dynamics of two CNTs with an initial point contact at varying angles for CNT lengths of up to 10 µm. We find that bundling times are an increasing function of initial collision angle and follow a power law with increasing CNT length that range from 10 −1 to 10 3 ns. We postulate that when this bundling time becomes of the same order as the CNT bundle collision time, the aerogel will form.

Synthesis of Carbon Nanotubes by Floating Catalyst Chemical Vapor Deposition and Their Applications

“…It was demonstrated that the time scale for CNT collision and bundle formation is 0.3-42 s. Recently, they proposed an adaptive mesoscale model for CNTs in a FCCVD system. [155] This model provides a tool to study the bundling dynamics and to show the aggregation state of CNTs. Also, they systematically investigated the formation process of nanoparticles and the supply of carbon source during continuous synthesis of CNT aerogel.…”

Densification of single-walled carbon nanotube films: Mesoscopic distinct element method simulations and experimental validation

“…Although mDEM has the necessary accuracy, developing faithful computational models for the CNT films described in Section 3 is still challenging. In addition to the difficulties associated with identifying the three-dimensionality of the film structure from the SEM and TEM images, we recognize that the multiscale structure observed by electron microscopy is the result of the vdW-driven CNT coagulation during synthesis, which involves direct CNT-CNT collisions in the gas phase, 21 and during and after the collection onto the filter substrate. While the former involves zipping of individual CNTs, the later stage is likely dominated by the bundle-bundle interaction processes.…”

“…Currently, the dynamical simulations of CNT films rely on numerical approaches, which are still under development and validation. In this respect, a recent theme in the development of numerical models is based on the idea of coarse-graining, [19][20][21][22] where the goal is to develop computationally tractable models of reduced complexity, while preserving a set of target properties to a sufficient accuracy. One of the first developed models was based on the simple bead-and-spring (B&S) polymeric chain model, 19 which is usually trained to reproduce elastic and adhesion properties of CNTs.…”

Highly Oriented Direct-Spun Carbon Nanotube Textiles Aligned by In Situ Radio-Frequency Fields

“…The CNT median diameters were analyzed to be 16.4, 18.9, and 25.4 nm for field intensities of 0.23, 0.35, and 0.75 kV cm –1 , respectively. Our recent study on collision rates between CNTs 54 and the alignment of CNTs into bundles 55 has shown few parameters with which to vary the number of CNTs per bundle and, thus, alter the fundamental aerogel structure. We hypothesize, on the basis of our previous work, that the characteristic collision time for aligned tubes increases (i.e., longer time between collisions) as the collision cross-section of two parallel linear structures is smaller.…”