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.
This innovation can be made compatible with matrices of other materials to facilitate fabrication of composites. Composite materials with polymer-coated SWNTs suspended in a polymer matrix have a novel structure of a suspended nanotube being smaller in its cross-sectional dimensions than the typical scale length of the individual polymer molecules in the matrix. This microscopic, dimensional compatibility minimizes the propensity of the composite to fail mechanically at the interface between the matrix and the SWNT, producing a composite material with enhanced properties such as strain-to-failure, toughness, and resistance to mechanical fatigue. These materials also serve as the active element for a range of transducers because they can change their physical dimensions in response to applied electric and magnetic fields. If treated with certain chemicals, the material can also change dimensionally and electronically in response to adsorption of chemicals on the nanotube surface, and can serve as chemical sensors and transducers.
This work was done by Richard E. Smalley and Michael J. O’Connell of Rice University and Kenneth Smith and Daniel T. Colbert of Carbon Nanotechnologies, Inc. for Johnson Space Center. For further information, contact the JSC Innovation Partnerships Office at (281) 483-3809.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
William M. Rice University
Office of Technology Transfer
6100 Main Street
Houston, TX 77005
Phone No.: (713) 348-6188
Refer to MSC-24070-1, volume and number of this NASA Tech Briefs issue, and the page number.