Metadynamics Simulations of Vinyl Polymer-Assisted Carbon Nanotube Dispersion for Next-Generation Batteries

Molecular dynamics simulations with enhanced sampling methods (metadynamics) are used to probe the mechanism of vinyl polymer-assisted carbon nanotube (CNT) dispersion in N-methyl-2-pyrrolidone (NMP). The polymer dispersants studied are polyvinylpyrrolidone (PVP), hydrogenated nitrile butadiene rubber (HNBR), and polystyrene (PS). It is determined how variations in the nature of the polymer side groups affect their mode of adsorption onto the CNT surface and, consequently, their effectiveness in dispersing CNTs. This correlation is established by comparing the free energy as a function of the distance between two parallel CNTs with and without added polymer. It is found that the adsorption of the pyrrolidone rings in PVP onto the CNT surface and the partial adsorption of the small polar nitrile groups in HNBR each result in disordered polymer layers that penetrate far into the solvent, and the interactions of the dangling polymer parts ensure that these extended protrusions translate to improved steric stabilization as compared to PS. This study not only presents a comprehensive methodology for assessing the effectiveness of polymer-assisted CNT dispersion but also establishes universal design principles for polymers with optimized performance.