Defect-free surface modification methods for solubility-tunable carbon nanotubes

Although carbon nanotubes (CNTs) have outstanding physical properties, there are still challenging issues such as poor dispersibility and miscibility between organic polymers and CNTs for polymer nanocomposites. Chemical modifications (e.g., strong acid based oxidation, carboxylation, etc.) can improve dispersion properties and compatibility, but such surface modification methods often lead to damage to the pristine CNT structure and also deteriorate the mechanical properties of CNTs. Here we demonstrate a simple, defect-free and scalable method for well-dispersed CNTs in common organic solvents, using dopamine and amine-terminated polyethylene glycol derivatives. This method makes it possible to prepare solubility-tunable CNTs without any severe structural deformation. As-modified CNTs were successfully characterized by thermal gravimetric analysis (TGA), Fourier-transformed infrared spectroscope (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscope (TEM). The surface modified-CNTs were well-dispersed in polar and/or non-polar common solvents. The well-dispersed CNTs can be used in a nanofiller in commercial polymers such as thermoplastic polyurethane (TPU) polymer. The CNT/TPU composite showed improved tensile strength without sacrificing elongation at break relative to those of pristine TPU.