Novel Materials Containing Single-Wall Carbon Nanotubes Wrapped in Polymer Molecules
- Wednesday, 01 July 2009
Coating carbon nanotubes in polymer molecules creates a new class of materials with enhanced mechanical properties for printed circuit boards, antenna arrays, and optoelectronics.
In this design, single-wall carbon nanotubes (SWNTs) have been coated in polymer molecules to create a new type of material that has low electrical conductivity, but still contains individual nanotubes, and small ropes of individual nanotubes, which are themselves good electrical conductors and serve as small conducting rods immersed in an electrically insulating matrix. The polymer is attached through weak chemical forces that are primarily non-covalent in nature, caused primarily through polarization rather than the sharing of valence electrons. Therefore, the electronic structure of the SWNT involved is substantially the same as that of free, individual (and small ropes of) SWNT. Their high conductivity makes the individual nanotubes extremely electrically polarizable, and materials containing these individual, highly polarizable molecules exhibit novel electrical properties including a high dielectric constant.
The polymer coating, however, greatly inhibits the Van der Waals attraction normally observed between separate, or small ropes of, SWNT. The polymer coating also interacts with solvents. The combination of the Van der Waals inhibition and the polymer-solvent interaction causes the wrapped nanotubes to be more readily suspended in solvents at high concentrations, which in turn substantially enables the manipulation of SWNT into many kinds of bulk materials including films, fibers, solids, and other types of composites. Also, the polymer-coated SWNT can be treated for the removal of the polymer molecules, restoring the SWNT to a pristine state.
Aggregations of the polymer-coated SWNT are substantially aligned and provide a new form of electrically-conducting rod composite, where the conducting rods have cross sectional dimensions on the nanometer scale and lengths of hundreds of nanometers or more. The electrical properties of the composite are highly anisotropic.