ReaxFF Reactive Force Field Study of Polymerization of a Polymer Matrix in a Carbon Nanotube-Composite System

Human transport to Mars and deep-space explorations demand the development of new materials with extraordinarily high performance-to-mass ratios. Promising candidates to fulfill these requirements are ultrahigh-strength lightweight materials, which consist of polymer matrices fortified by pristine carbon nanotubes (CNTs). Previous investigations have showed that with an increase in the CNT diameter, its preferred configuration changes from a circular form to a flattened shape that can be obtained under high pressure or tension conditions. The ReaxFF reactive force field can reveal detailed chemical interactions at the atomistic scale. To enable ReaxFF simulations on CNT/polymer interfaces, we trained force-field parameters to capture the proper structure of flattened CNTs (flCNTs), i.e., dumbbell-like shape CNTs, against available polymer consistent force field-interface force field data, which have good proximity to density functional theory data. In this study, we used accelerated ReaxFF molecular dynamics simulation using the optimized force field to study the polymerization of diglycidyl ether of bisphenol F and diethyltoluenediamine molecules in the vicinity of circular and flCNTs. Our results indicate that the flat regions of flCNTs are more favorable spots for the polymers to settle compared to the curved regions due to the higher binding energies. Moreover, higher dimer generation around flCNTs results in more effective coating of the nanotube, which leads to higher load transfer when compared to circular CNTs. According to our results, there is high alignment between polymers and the nanotube surface, which is due to the strong p-p interactions of aromatic carbon rings in the polymers and nanotubes. These atomistic ReaxFF simulations indicate the capability of this method to simultaneously observe the polymerization of monomers along with their interactions with CNTs.