Surface Modifications of Single-Wall Carbon Nanotubes

摘要

In order to manufacture high performance nanocomposites comprising single-wall carbon nanotubes (SWNT) in organic matrices that take advantage of the unique mechanical and physical properties of the nanotubes, two major hurdles must first be overcome. These are 1) the strong Vander Waals forces that cause SWNTs to agglomerate in bundles (called ropes) and 2) smooth nanotube surfaces that interact only weakly with polymeric matrices. If surface modification techniques are developed that can enhance SWNT dispersion and interaction with organic matrices, the truly revolutionary properties of carbon nanotubes can be harnessed for nanocomposite reinforcement. Early nanotube research focused on functionalization through the carboxylic acid SWNT end groups, but modification of the SWNT ends groups alone will not provide sufficient compatibilization to allow significant load transfer from organic matrices into the body of the SWNTs. Sidewall functionalization performed by different methods, including fluorination followed by alkyl-lithiation, and free- radical reaction, has also been employed for surface modification and should lead to enhanced load transfer. This approach may enhance mechanical properties of SWNT composites, but it modifies the SWNT electronic structure and disrupts their electrical conductivity. It is therefore not indicated for applications that depend upon the thermal and electrical conductivity of the nanotube filler. Surface compatiblization shows the highest promise as a method for increasing dispersion and load transfer for such applications. Previous work has achieved marked improvement in de-agglomeration of SWNT ropes, but known compatiblizers work primarily in water and do not lend themselves to transfer into organic matrices. Foster-Miller and Carbon Nanotechnologies, Inc. are currently extending this work to the study of polymeric dispersants for use in organic solvents. A brief review of the state of the art and a summary of the current work are included in this paper.