Alrawashdeh Ahmad I, Lagowski Jolanta B
Department of Physics and Physical Oceanography, Memorial University of Newfoundland St. John's NL Canada A1B 3X7
RSC Adv. 2018 Aug 29;8(53):30520-30529. doi: 10.1039/c8ra02460j. eCollection 2018 Aug 24.
Among different dispersants of single-walled carbon nanotubes (SWCNTs), conjugated organic oligomers have the ability to interact strongly with SWCNTs and allow for effective dispersion in several organic solvents. Recently, we have carried out two computational investigations on the intermolecular interactions between conjugated organic oligomers and SWCNTs in order to gain insight into an important process of the non-covalent dispersion of carbon nanotubes with short oligomers. These studies highlighted the fact that two additional factors, namely, the effects of the solvent and the carbon nanotube's size on these interactions need further investigation. In this work, with the help of model compounds (which are molecular fragments of the short oligomers used in our previous investigations), we analyze the significance of these two factors. We employ three dispersion corrected density functional theory (D-DFT) approximations (B97D, wB97XD, and B3LYP-D3) to assess the effect of the DFT method, and two basis sets (6-31G(d) and 6-31++G(d,p)) to assess the importance of using a higher basis set in our computations. The main focus of this work is to assess the effect of solvation and nanotube's size on the structure, electronic properties, and binding energies of the respective pairs of model compounds and segments of carbon nanotubes. No significant differences are found between the results of (6,5) and (8,7) SWCNTs in either the geometrical parameters of interacting oligomers or the general tendency of wrapping of their long side chains (SCs) around the nanotubes. However, we find that the binding energies per atom between nanotubes and model compounds are larger for nanotubes with the smaller diameter. The results of electronic properties also show that all model compounds interact more strongly with the (6,5) SWCNT than with the (8,7) SWCNT. Polar solvents such as chloroform show lower binding energies relative to those obtained without a solvent or with non-polar solvents such as hexane. It appears that the presence of a solvent weakens the oligomer/nanotube interactions and, presumably, strengthens the oligomer/solvent and nanotube/solvent interactions to facilitate dispersion of SWCNTs.
在单壁碳纳米管（SWCNT）的不同分散剂中，共轭有机低聚物能够与SWCNT发生强烈相互作用，并能在几种有机溶剂中有效分散。最近，我们对共轭有机低聚物与SWCNT之间的分子间相互作用进行了两项计算研究，以便深入了解碳纳米管与短低聚物非共价分散的一个重要过程。这些研究突出了两个额外因素，即溶剂和碳纳米管尺寸对这些相互作用的影响需要进一步研究。在这项工作中，借助模型化合物（它们是我们之前研究中使用的短低聚物的分子片段），我们分析了这两个因素的重要性。我们采用三种色散校正密度泛函理论（D-DFT）近似方法（B97D、wB97XD和B3LYP-D3）来评估DFT方法的效果，并使用两个基组（6-31G(d)和6-31++G(d,p)）来评估在我们的计算中使用更高基组的重要性。这项工作的主要重点是评估溶剂化和纳米管尺寸对模型化合物与碳纳米管各对之间的结构、电子性质和结合能的影响。在相互作用的低聚物的几何参数或其长侧链（SC）围绕纳米管缠绕的一般趋势方面，(6,5)和(8,7) SWCNT的结果之间未发现显著差异。然而，我们发现，对于直径较小的纳米管，纳米管与模型化合物之间的每原子结合能更大。电子性质的结果还表明，所有模型化合物与(6,5) SWCNT的相互作用都比与(8,7) SWCNT的相互作用更强。相对于无溶剂或使用己烷等非极性溶剂时获得的结合能，氯仿等极性溶剂显示出较低的结合能。似乎溶剂的存在会削弱低聚物/纳米管相互作用，并且大概会增强低聚物/溶剂和纳米管/溶剂相互作用，以促进SWCNT的分散。
