Surface modification methods and mechanisms in carbon nanotubes dispersion

Carbon nanotubes (CNTs) as functional materials have aroused great interest among researchers due to their remarkable mechanical, electrical, thermal, and other photoelectric properties. However, CNTs tend to agglomerate into crystalline bundles because of the strong Van der Waals attraction force, adversely affecting their properties. This tendency to self-aggregate has been an important barrier to their chemical and physical manipulation and thus to their practical applications. To overcome this barrier, advances in the maximum-effective dispersion (denoted as mono-dispersion) of CNTs in the liquid phase (water and organic solvent) or solid remain critical to realizing many important commercial applications. Herein we summarize recent breakthroughs in the strategies of CNTs dispersion and highlight the key ongoing research challenges. Studies for currently understanding the aggregation and dispersion kinetics of CNTs are mainly consisting of two aspects, covalent or non-covalent bonding functionalization, which are usually introduced to nullify or reduce their Van der Waals force, thus improving their self-assembling characteristics. In particular, the roles of non-covalent bonding modifications, including electrostatic interaction, π-π stacking interaction, dipole interactions, Van der Waals interactions, hydrogen bond, and coordination, are more attractive in CNTs dispersion without disturbing their internal electronic structure. The surface modification techniques and potential applications are also highlighted.