Debundling and dispersion of carbon nanotubes (CNTs) in polymer solutions play a major role in the preparation of carbon nanofibers due to early effects on interfacial ordering and mechanical properties. A roadblock toward ultrastrong fibers is the difficulty to achieve homogeneous dispersions of CNTs in polyacrylonitrile (PAN) and poly(methyl methacrylate) (PMMA) precursor solutions in solvents such as dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAc), and N,N-dimethylformamide (DMF). In this contribution, molecular dynamics simulations with accurate interatomic potentials for graphitic materials that include virtual π electrons are reported to analyze the interaction of pristine single wall CNTs with the solvents and polymer solutions at 25 °C. The results explain the barriers toward dispersion of SWCNTs and quantify CNT-solvent, polymer-solvent, as well as CNT-polymer interactions in atomic detail. Debundling of CNTs is overall endothermic and unfavorable with dispersion energies of +20 to +30 mJ/m in the pure solvents, + 20 to +40 mJ/m in PAN solutions, and +20 to +60 mJ/m in PMMA solutions. Differences arise due to molecular geometry, polar, van der Waals, and CH-π interactions. Among the pure solvents, DMF restricts CNT dispersion less due to the planar geometry and stronger van der Waals interactions. PAN and PMMA interact favorably with the pure solvents with dissolution energies of -0.7 to -1.1 kcal per mole monomer and -1.5 to -2.2 kcal per mole monomer, respectively. Adsorption of PMMA onto CNTs is stronger than that of PAN in all solvents as the molecular geometry enables more van der Waals contacts between alkyl groups and the CNT surface. Polar side groups in both polymers prefer interactions with the polar solvents. Higher polymer concentrations in solution lead to polymer aggregation via alkyl groups and reduce adsorption onto CNTs. PAN and PMMA solutions in DMSO and dilute solutions in DMF support CNT dispersion more than other combinations whereby the polymers significantly adsorb onto CNTs in DMSO solution. The observations by molecular simulations are consistent with available experimental data and solubility parameters and aid in the design of carbon nanofibers. The methods can be applied to other multiphase graphitic materials.

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REACTER is a heuristic protocol that allows complex, predefined reactions to be modeled in atomistic, fixed-valence molecular dynamics (MD) simulations. The method is applicable to a broad range of chemical reactions and permits much larger and longer reactive simulations than existing approaches. One or more competing multistep reactions or series of reactions can be invoked simultaneously. Special treatment can be applied to neighboring atoms to relax high-energy configurations while the simulation progresses. The original implementation of REACTER, which was included in the open-source LAMMPS simulation package as fix bond/react, was only available for serial simulations. This work describes the expansion of the REACTER protocol for use in parallel simulations, as well as the addition of various new options, including deletion of reaction byproducts, reversible reactions, and custom reaction constraints. The capability of the parallel implementation is demonstrated through large-scale simulations (200000+ atoms) of the polymerization of polystyrene and nylon-6,6. The morphologies of both polymers are analyzed after reaching >99% extent of polymerization. Finally, the newly added reversible reactions feature is demonstrated by rupturing these highly entangled systems under uniaxial strain by defining a chain scission reaction.

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The long‐term stability of direct carbon fuel cells, based on solid oxide fuel cells with molten Sb and Sb–Bi anodes, was examined for operation with activated charcoal, rice starch, and bio‐oil fuels at 973 K. With intermittent stirring of the fuel–metal anode interface, the anode performance was stable, and reasonable power densities (∼250 mW/cm2) were achieved for periods up to 250 h. With Sc‐stabilized zirconia, severe thinning of the electrolyte occurred in regions of high current flow. No electrolyte thinning was observed with yttria‐stabilized zirconia as the electrolyte operating at the same current densities. © 2012 American Institute of Chemical Engineers AIChE J, 59: 3342–3348, 2013