Dispersion of Single-Walled Carbon Nanotubes with Oligo(<i>p</i>‑phenylene ethynylene)s: A DFT Study

Pure carbon nanotubes (CNT) and CNT–polymer composites have many useful properties, ranging from electrical conductivity to superior mechanical strength. However, the full potential of using CNTs as reinforcements (in a polymer matrix, for example) has been severely limited because of complications associated with the dispersion of CNTs. CNTs tend to entangle with each other, forming materials with properties that fall short of expectations. One of the effective ways of dispersing CNTs is the use of short π-conjugated oligomers like oligo­(<i>p</i>-phenylene ethynylene)­s (OPEs) as dispersants. In this study, we provide a comprehensive investigation of the interactions between single-walled CNTs (SWCNTs) and OPEs with two different end groups; aldehyde (ALD) and dithiafulvene (DTF). The hybrid B3LYP and the dispersion (D)- and/or the long-range (LR)-corrected density functional theory (DFT) methods such as B97D, wB97XD, and CAM-B3LYP with the 6-31G­(d) basis set are employed in obtaining electronic structure information (dipole moments and energy levels) for the gas-phase (single) oligomers and the (6,5) SWCNT and their combinations. In addition, the D- and/or LR-corrected DFT methods are used in determining binding energies and intermolecular distances for the OPE/SWCNT combinations. We focus on understanding the roles of oligomer’s end groups and side chains in the dispersion of SWCNTs. In agreement with the experimental observations, the electronic structure and the binding energy results show that OPE-DTF interacts more strongly with the SWCNT than OPE-ALD. This work also provides insight into why OPEs end-capped with DTFs are much more effective in the dispersion of CNTs than OPEs end-capped with ALDs. Furthermore, this computational analysis can be of use in choosing an appropriate D- and/or LR-corrected DFT method when studying properties of systems containing CNTs