The subtle and efficient manufacture of high-quality carbonaceous materials dominates their extensive applications. Meanwhile, revealing the underlying mechanism in the formation of carbonaceous materials is crucial to improving their manufacture efficiency. In the present work, we focus upon the pyrolysis mechanism for four light hydrocarbons including methane, CH4, ethane, C2H6, ethylene, C2H4, and acetylene, C2H2, to carbonaceous materials, combined with reactive molecular dynamics (RMD) simulations. The carbonaceous materials with various morphologies are observed in our simulations, and the morphologies are strongly dependent on the initial reactants; i.e., a disorderly C cluster, a crossed C multilayer, and an orderly C monolayer are made from C2H2, C2H4, and C2H6 and CH4, respectively, as ascertained partly in experiments. Tracing the RMD trajectories, we confirm that the pyrolysis of all four light hydrocarbons undergoes three stages, including the C chain elongation with generation of new small carbonaceous molecules or radicals, the formation and growth of polycyclic aromatic hydrocarbons, and the stable growth of C clusters. The morphologic difference of the final C clusters is attributed to the reactant activity and C growth styles. That is, the higher activity and the faster growth by the C2 addition facilitate the more disorderly arrangement of C atoms, and vice versa. Typically, the dense C2H2 tends to form disorderly C black, while the thin CH4, to orderly C nanotubes. It shows that selecting the reactants in terms of their activities is a key to preparing orderly carbonaceous materials. These findings are expected to be useful to understand the formation mechanism and design techniques for efficiently manufacturing high-quality carbonaceous materials.

Learning the micro-mechanisms of fluorinated polymers during mechanical response is more difficult than that of common polymers due to the unique intrinsic characteristics of the fluorine element. In this paper, we applied molecular dynamics simulations to study deformation mechanisms of poly(vinylidine fluoride-co-chlorotrifluoroethylene) during uniaxial tension. We analyzed the variations of individual energy components and structural distribution curves versus strain in addition to the commonly used stress-strain curves and microstructure evolutions during stretching. The elastic limit is ɛ = 0.02, ɛ = 0.06 is the yield point, ɛ = 0.24 is the termination of the softening, necking occurs at 0.24 < ɛ < 0.5, strain hardening occurs at 0.5 < ɛ < 2.6, and ɛ = 2.6 is the damage or brake point. The elastic behavior of the material does not rely on strain rate, the obvious effect of strain rate can be seen at the yield region and strain softening region, and the stress values are not influenced by strain rates at the softening and hardening stages. Overall, total potential energy is mainly correlated with non-bonded energy, and the proportion of ΔE overwhelms all the others. The energy components are ordered: ΔE > ΔE > > ΔE > ΔE > ΔE. The chain conformation at yield point is almost unchanged compared with the pre-stretching conformation. The chain conformations at the end of strain softening changes more obviously than that at yield point. The molecular chains maintain random coil structure before strain hardening, and switch into a stretch chain conformation gradually during strain hardening. The maximum change in bond angle during the stretching process is F-C-H, the largest change in bond length is the C-Cl bond, and the largest change in dihedral angle is H-C-C-H. The change of non-bonded interaction in the poly(VDF-co-CTFE) system is much larger than the bonding interaction, and the main factor affecting bonding interaction is the change of angles. Graphical abstract Poly(vinylidine fluoride-co-chlorotrifluoroethylene) during tensionᅟ.

Elucidating the mechanical response of diamond is a difficult task due to its ultrahard nature. Here, we applied a molecular dynamics (MD) method to investigate the mechanical response of single-crystal diamond under nanoindentation. There was no obvious "pop in" phenomenon on the load-depth curve, and the elastic modulus deduced from the curve was 1128 GPa, which was similar to the value obtained from experimental measurements. Results from computed tomography (CT) and the coordination number showed that the distribution of the mismatched C atoms around the deformation zone took the form of a 'double cross.' The atoms around the indenter tip could be divided into two zones, a translation zone and a lattice distortion zone, based on their movements. Subsequent first-principles calculations revealed that the C-atom displacement barrier varied significantly with direction, which resulted in shear stress between the two zones and the formation of the double-cross splitting. Graphical Abstract The displacement of the atoms around the indenter tip.