Theoretical Studies\nfor Improving the Dispersion of\nCarbon Nanotubes in Caprolactam Polymers by Enhancing the Intermolecular\nInteractions with Functionalization: Implications for Reinforced Polymer\nComposites

The inhomogeneous dispersion caused\nby carbon nanotube (CNT) agglomeration\nin composites still needs to be explored, though mechanical properties\nof the polymer materials can be improved significantly if CNTs were\nadded as a reinforcement. In this work, to explore an effective way\nto solve the agglomeration problem of CNTs within polycaprolactam\n(Nylon66), a functionalization strategy to enhance the intermolecular\ninteraction between the caprolactam (CPL) unit molecule and (7,3)\nsingle-walled carbon nanotube (SWCNT) was investigated theoretically\nat the molecular level. Molecular moving behavior and intermolecular\ninteraction energy indicate that the surface functionalization, especially\nwith the –NH<sub>2</sub> group, is an effective way to strengthen\nthe interaction between CPL and (7,3) SWCNTs, which highlights the\nkey role of controlled surface functionalization of CNTs in improving\nits dispersion degree in polycaprolactam. This can be explained by\na small interfacial charge-transfer amount, which occurs from the\noccupied valence band maximum of (7,3) SWCNTs to the occupied highest\noccupied molecular orbital of the CPL molecule. In this case, the\ndipole moment of involved molecules plays an important role in the\ninterfacial interaction strength and then increased intermolecular\ninteraction between CPL and functionalized (7,3) SWCNTs, especially\nincorporating the –NH<sub>2</sub> group with larger dipole\nmoment, can be understood. Our results for the functionalization effects\non the physical adsorption behavior of organic molecules around (7,3)\nSWCNTs can provide more useful information for further design and\noptimization of a SWCNT-based reinforcement.