Dispersion of Single-Walled Carbon Nanotubes with Oligo(p-phenylene ethynylene)s: A DFT Study

Abstract

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(p-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.

The role of the solvent and the size of the nanotube in the non-covalent dispersion of carbon nanotubes with short organic oligomers – a DFT study

“…With regard to the applicability of the present, short model compound study, to the previous larger model 23,24 investigations, we make the following comment. In Table 3 in ref.…”

“…1) and two segments of (6,5) and 8,7SWCNTs are considered in this study. These molecules are fragments of the OPE and DPF oligomers used in previous computational 23,24 and experimental 20,22 works.…”

“…Although this work concentrates on studying the effect of solvation and nanotube's size on the interactions between the oligomers and SWCNTs, the effect of D-DFT method and basis set is also briey investigated. It is clear from our previous works, 23,24,[30][31][32] that B97D and B3LYP-D3 methods are the most recommended for investigating properties of organic combinations at the interfacial region since they gave results that were consistent with experimental observations and/or trends. In this work, we have primarily employed the B97D method since it is less computationally intensive than the B3LYP-D3 (or wB97xD).…”

“…As in our previous works, 23,24 to assess the strength of molecule/nanotube interactions, the binding energies (E b ) between studied molecules and SWCNTs are computed,…”

“…22). Our previous computations, 23,24 which involved pairs consisting of an OPE or DPF oligomer and a sizable segments of (6,5) SWCNT (diameter ¼ $0.75 nm), are very intensive and take a very long time to carry out even with 6-31-G(d) basis set.…”