(750f) An Accurate Force Field for Graphitic Materials Including Virtual Pi Electrons and Applications to Understand Carbon Nanotube Dispersion in Solvents and Polymer Solutions

A new, compatible all-atom force field for graphene, graphite, carbon nanotubes and related materials is introduced as part of the Interface force field (IFF) that enables improvements in the reproduction of surface energies, hydration energies, contact angles, cation-pi interactions, and prediction of multiphase assembly by an order of magnitude compared to earlier models. The models are compatible with IFF, PCFF, CVFF, CHARMM, and several other force fields. Molecular dynamics simulations with these interatomic potentials that include virtual π electrons are reported to explain the interaction of pristine single wall CNTs with solvents and polymer solutions at 25 °C. Debundling and dispersion of carbon nanotubes (CNTs) in polymer solutions plays 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). The results quantify CNT-solvent, polymer-solvent, as well as CNT-polymer interactions in atomic detail, including wrapping of PMMA around CNTs which remarkably changes interfacial properties. Quantitative comparisons with solubility parameters and experimental data are reported. See details in: Pramanik et al. ACS Nano 2017, 11, 12805-12816.