Influence of the wetting behavior and surface energy on the dispersibility of multi-wall carbon nanotubes

Carbon nanotubes (CNTs) possess extraordinary particle properties which make them ideal for the development of innovative polymer composite materials. Because of the tendential agglomerate forming of CNTs, their homogenous exfoliation in organic or inorganic phases is often required and can be obtained by mechanical stressing of the agglomerates. However, the CNT-exfoliation is only achievable in few fluids. Therefore, the CNT-functionalization which means the covalent attachment and modification of the particle surface with functional groups or molecules is applied to alter particle interactions and in this way, their dispersing behavior. The poor CNT-dispersibility in fluids and CNT-dispersion strategies as the functionalization show the importance of the characterization of their particle interactions.In order to describe CNT/fluid-interactions the wetting behavior was characterized by contact angle measurements with the capillary liquid penetration method. The CNT-surface energies regarding Owens and Wendt could be estimated from the measured contact angles. Thereby, non-modified CNTs exhibited a good interaction with molecules of longer alkyls and even polar liquids and showed further a significant dispersive and polar fraction of the surface energy. The determined surface energies were used for the explanation and estimation of the CNT-dispersibility in liquids. Successful dispersions could be achieved with fluids of similar dispersive and polar fractions compared with those of the particles. Furthermore, ethylamine-functionalized CNTs possessed an enhanced polar component of their surface energy which demonstrated that the CNT/fluid-interactions can be controlled by covalent CNT-functionalization.