Implementing reactivity in molecular dynamics simulations with harmonic force fields
Not provided.
Science & Technology - Other Topics↗
Engineering topics
Damirchi, Behzad
Publications and source records attributed to Damirchi, Behzad.
Molecular Alignment of a Meta-Aramid on Carbon Nanotubes by In Situ Interfacial Polymerization
Molecularly organized nanocomposites of polymers and carbon nanotubes (CNTs) have great promise as high-performance materials; in particular, conformal deposition of polymers can control interfacial properties for mechanical load transfer, electrical or thermal transport, or electro/chemical transduction. However, controllability of polymer-CNT interaction remains a challenge with common processing methods that combine CNTs and polymers in melt or in solution, often leading to nonuniform polymer distribution and CNT aggregation. In this work, we demonstrate CNTs within net-shape sheets can be controllably coated with a conformal coating of meta-aramid by simultaneous capillary infiltration and interfacial polymerization. We determine that π-interaction between the polymer and CNTs results in chain alignment parallel to the CNT outer wall. Subsequent nucleation and growth of the precipitated aramid forms a smooth continuous layered sheath around the CNTs. These findings motivate future investigation of mechanical properties of the resulting composites, and adaptation of the in situ polymerization method to other substrates.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Converting PBO fibers into carbon fibers by ultrafast carbonization
Here, we report an ultrafast transformation of poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibers into car- bon fibers (CFs) by direct carbonization that eliminates high-cost oxidation in traditional CF conversion. Ultrafast heating and cooling render PBO-derived CFs superlative mechanical properties. ReaxFF atomistic-scale reactive molecular dynamics simulations unveil the PBO to CF conversion mechanism in which ultrafast heating suppresses the O-contained gas release, facilitating all-carbon rings alignment during the carbonization of PBO. These results offer new guidelines for identifying and evaluating alternative CF precursors and fresh perspectives on smart manufacturing of CFs.
42 ENGINEERING↗
Atomistic Scale Analysis of the Carbonization Process for C/H/O/N-Based Polymers with the ReaxFF Reactive Force Field
During the carbonization process of raw polymer precursors, graphitic structures can evolve. The presence of these graphitic structures affects mechanical properties of the carbonized carbon fibers. To gain a better understanding of the chemistry behind the evolution of these structures, we performed atomistic-scale simulations using the ReaxFF reactive force field. Three different polymers were considered as a precursor: idealized ladder PAN (polyacrylonitrile), a proposed oxidized PAN, and poly(p-phenylene- 2,6-benzobisoxazole). We determined the underlying molecular details of polymer conversion into a carbon fiber structure. Because these are C/H/O/ N-based polymers, we first developed an improved force field for C/H/O/N chemistry based on the density functional theory data with a particular focus on N2 formation kinetics and its interactions with polymer-associated radicals formed during the carbonization process. Then, using this improved force field, we performed atomistic-scale simulations of the initial stage of the carbonization process for the considered polymers. On the basis of our simulation data, the molecular pathways for the formation of low-molecular-weight gas species and all-carbon ring formation were determined. We also examined the possible alignment of the developed all-carbon 6-membered ring clusters, which is crucial for the further graphitic structure evolution.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗