Conductive Polymeric Nanocomposite Materials

August 1, 2006

AFRL scientists have developed a method for uniformly dispersing carbon nanofibers throughout polymeric materials to increase their conductivity. Engineers will be able to employ the resulting polymeric nanocomposites in conductive paints, coatings, caulks, sealants, adhesives, fibers, thin films, thick sheets, tubes, and large structural components needed for both aerospace and industry applications.

In performing nanoscience research, materials scientists seek to observe and ultimately manipulate materials and their properties on the nanoscale. Nanoscience and technology affords unique opportunities to create revolutionary material combinations. Such combinations enable new properties and exploit the synergism existing between constituent materials only when the materials' morphology and fundamental physics coincide at the nanoscale. Adding carbon nanofibers into a polymeric material enhances the material's dimensional stability, abrasion resistance, electrical and thermal conductivity, and tribological properties (e.g., reduced surface friction).

A scanning electron microscope image of a thermoplastic polyurethane material containing uniformly dispersed nanofibers. The mixing process preserved the nanofibers’ aspect ratio (length to diameter), which is key to the material’s high conductivity.

Scientists from AFRL and the University of Dayton Research Institute (UDRI) initiated an in-house research program with the goal of developing conductive nanocomposites using low-cost, multiwalled nanotubes. This concept held significant promise for a variety of commercial and military applications but was largely unexplored prior to this program. The collaborative effort ultimately yielded a proven process for uniform dispersement of vapor-grown carbon nanofibers throughout a wide variety of polymer matrices (see figure on previous page). The method combines nanofibers with a solvent to form a solution and then introduces a polymer to the original solution to form another, nearly homogeneous mixture. Evaporation or coagulation subsequently removes the solvent from the mixture.

The researchers found that the polymers best suited for this process reside in the polyurethane, polyimide, epoxy resin, silicone polymer, and aromatic heterocyclic rigid-rod and ladder polymer groups. Likewise, their results indicate that the most successful solvents for this process come from the group consisting of dimethyl sulfoxide; tetrahydrofuran; acetone; methanesulfonic acid; polyphosphoric acid; and N,N-dimethyl acetamide. Their experiments also suggest that both the polymer and the solvent should be somewhat polar.

UDRI filed the patent application, and the Air Force subsequently transitioned the methodology to PRCDeSoto International, Inc. UDRI is now pursuing commercial application of the technology, and NanoSperse, LLC (Beavercreek, Ohio), has developed and prepared master batches of conductive nanocomposites for technology transfer. AFRL is currently conducting follow-on research to investigate the development of a metalcoated nanotube for use in nanocomposites. This material would provide improved conductivity for applications such as signal wire shielding, where reduced thickness and increased conductivity are imperative.

Materials scientists will ultimately use this patented process to develop a wide variety of commercial and military applications for aerospace, electronics, automotive, and chemical markets. Some of the specific technology areas that will benefit from conductive nanocomposite materials are electromagnetic interference shielding and pulse hardening; electrical signal transfer; electrostatic painting; electrostatic discharge; and various electrooptical devices, such as photovoltaic cells.

Dr. Max D. Alexander and Mr. Tim Anderl (Anteon Corporation), of the Air Force Research Laboratory's Materials and Manufacturing Directorate, wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at http://www.afrl.af.mil/techconn_index.asp . Reference document ML-H-05-10.