Evolution of Glassy Carbon Derived from Pyrolysis of Furan Resin.

Glassy carbon (GC) material derived from pyrolyzed furan resin was modeled by using reactive molecular dynamics (MD) simulations. The MD polymerization simulation protocols to cure the furan resin precursor material are validated via comparison of the predicted density and Young's modulus with experimental values. The MD pyrolysis simulations protocols to pyrolyze the furan resin precursor is validated by comparison of calculated density, Young's modulus, carbon content, sp carbon content, the in-plane crystallite size, out-of-plane crystallite stacking height, and interplanar crystallite spacing with experimental results from the literature for furan resin derived GC.

Voxelized Atomic Structure Potentials: Predicting Atomic Forces with the Accuracy of Quantum Mechanics Using Convolutional Neural Networks.

This paper introduces voxelized atomic structure (VASt) potentials as a machine learning (ML) framework for developing interatomic potentials. The VASt framework utilizes a voxelized representation of the atomic structure directly as the input to a convolutional neural network (CNN). This allows for high-fidelity representations of highly complex and diverse spatial arrangements of the atomic environments of interest.

Simulating the effects of carbon nanotube continuity and interfacial bonding on composite strength and stiffness.

Molecular dynamics simulations of carbon nanotube (CNT) composites, in which the CNTs are continuous across the periodic boundary, overestimate the experimentally measured mechanical properties of CNT composites along the fiber direction. Since the CNTs in these composites are much shorter than the composite dimensions, load must be transferred either directly between CNTs or through the matrix, a mechanism that is absent in simulations of effectively continuous CNTs. In this study, the elastic and fracture properties of high volume fraction discontinuous carbon nanotube/amorphous carbon composite systems were compared to those of otherwise equivalent continuous CNT composites using ReaxFF reactive molecular dynamics simulations.

Chemical Reactions in Classical Molecular Dynamics.

An algorithm capable of incorporating multi-step reaction mechanisms into atomistic molecular dynamics (MD) simulations using traditional fixed valence force fields is proposed and implemented within the framework of LAMMPS (Large-scale Atomic Molecular Massively Parallel Simulator). This extension, referred to as , enables bonding topology modifications during a running MD simulation using pre- and post-reaction bonding templates to carry out a pre-specified reaction. Candidate reactants are first identified by interatomic separation, followed by the application of a generalized topology matching algorithm to confirm they match the pre-reaction template.

Multifunctional Electroactive Nanocomposites Based on Piezoelectric Boron Nitride Nanotubes.

Space exploration missions require sensors and devices capable of stable operation in harsh environments such as those that include high thermal fluctuation, atomic oxygen, and high-energy ionizing radiation. However, conventional or state-of-the-art electroactive materials like lead zirconate titanate, poly(vinylidene fluoride), and carbon nanotube (CNT)-doped polyimides have limitations on use in those extreme applications. Theoretical studies have shown that boron nitride nanotubes (BNNTs) have strength-to-weight ratios comparable to those of CNTs, excellent high-temperature stability (to 800 °C in air), large electroactive characteristics, and excellent neutron radiation shielding capability.

Simulation of the Elastic and Ultimate Tensile Properties of Diamond, Graphene, Carbon Nanotubes, and Amorphous Carbon Using a Revised ReaxFF Parametrization.

In light of the enduring interest in using nanostructured carbon materials as reinforcing elements in composite materials, there is a significant need for a reliable computational tool capable to predict the mechanical properties, both elastic properties and properties at the point of fracture, in large-scale atomistic simulations. A revised version of the ReaxFF reactive force field parametrization for carbon, ReaxFFC-2013, was recently published and is notable because of the inclusion of density functional theory (DFT)-derived mechanical data for diamond and graphite in the fitting set. The purpose of the present work is to assess the accuracy of this new force field for predicting the mechanical properties for several allotropes of carbon, both in the elastic regime and during fracture.

The effect of time step, thermostat, and strain rate on ReaxFF simulations of mechanical failure in diamond, graphene, and carbon nanotube.

As the sophistication of reactive force fields for molecular modeling continues to increase, their use and applicability has also expanded, sometimes beyond the scope of their original development. Reax Force Field (ReaxFF), for example, was originally developed to model chemical reactions, but is a promising candidate for modeling fracture because of its ability to treat covalent bond cleavage. Performing reliable simulations of a complex process like fracture, however, requires an understanding of the effects that various modeling parameters have on the behavior of the system.

Toward high performance thermoset/carbon nanotube sheet nanocomposites via resistive heating assisted infiltration and cure.

Thermoset/carbon nanotube (CNT) sheet nanocomposites were successfully fabricated by resistive heating assisted infiltration and cure (RHAIC) of the polymer matrix resin. Resistive heating takes advantage of the electrical and thermal conductivity of CNTs to rapidly and uniformly introduce heat into the CNT sheet. Heating the CNT sheet reduces the viscosity of the polymer resin due to localized temperature rise in close proximity to the resin, which enhances resin flow, penetration, and wetting of the CNT reinforcement.

Polyaniline/carbon nanotube sheet nanocomposites: fabrication and characterization.

Practical approaches are needed to take advantage of the nanometer-scale mechanical properties of carbon nanotubes (CNTs) at the macroscopic scale. This study was conducted to elucidate the salient factors that can maximize the mechanical properties of nanocomposites fabricated from commercially available CNT sheets. The CNT sheets were modified by stretching to improve CNT alignment and in situ polymerization using polyaniline (PANI), a π-conjugated conductive polymer, as a binder.

Parametric Study of ReaxFF Simulation Parameters for Molecular Dynamics Modeling of Reactive Carbon Gases.

The development of innovative carbon-based materials can be greatly facilitated by molecular modeling techniques. Although the Reax Force Field (ReaxFF) can be used to simulate the chemical behavior of carbon-based systems, the simulation settings required for accurate predictions have not been fully explored. Using the ReaxFF, molecular dynamics (MD) simulations are used to simulate the chemical behavior of pure carbon and hydrocarbon reactive gases that are involved in the formation of carbon structures such as graphite, buckyballs, amorphous carbon, and carbon nanotubes.

In situ mechanical property measurements of amorphous carbon-boron nitride nanotube nanostructures.

To understand the mechanical properties of amorphous carbon (a-C)/boron nitride nanotube (BNNT) nanostructures, in situ mechanical tests are conducted inside a transmission electron microscope equipped with an integrated atomic force microscope system. The nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation. We demonstrate multiple in situ tensile, compressive, and lap shear tests with a-C/BNNT hybrid nanostructures.

Ultrafast dynamics of single-walled carbon nanotubes dispersed in polymer films.

Wavelength-resolved femtosecond transient absorption spectroscopy is used to follow the electronic dynamics of single-walled carbon nanotubes in polymers following visible photoexcitation. Electron-hole (e-h) pairs give rise to sharp features in the transient spectra that decay in amplitude and exhibit rapid spectral shifts. The decay reflects (e-h) recombination on both short (1.