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Our Technologies: Low-Cost Nano Materials

    (B) Nano-scaled Graphene Platelets (NGPs) – Low-cost Alternatives to Carbon Nanotubes (CNTs) and Carbon Nano-fibers (CNFs) (Results of a DOE SBIR Project; a portfolio of 12 patents pending or issued)

 e.g., B. Z. Jang and W. C. Huang, “Nano-scaled Graphene Plates,” U.S. Pat. No. 7,071,258 (07/04/2006).

Nanocomposites and Carbon Nanotubes:  Nanocomposites possess unique features and functions unavailable in conventional fiber-reinforced and unreinforced polymers. One revolutionary nano-scaled filler development in recent years is the carbon nanotube (CNT), which is expected to play a significant role in the design and manufacture of nano-structured components, nanocomposites, nano-electro-mechanical systems (NEMS), functional coatings, and substrates for microelectronic devices and structural components.  However, attempts to produce CNT in large quantities have been fraught with overwhelming challenges due to poor yield and costly fabrication and purifying processes. 

Enhancement in strength and stiffness for nanoscale reinforcement is well documented in the literature. The improvement in barrier properties in the nanocomposites derived from layered silicates, or smectite clays, has been well studied in recent years. Unfortunately, nano-clay reinforced polymers do not possess as good electrical conductivity, thermal, and dielectric properties as some functional composites such as carbon black-, metallic powder-, and graphite-containing polymers. A need exists for developing a nanocomposite that contains a minimal filler concentration for reduced costs and weight. Another need exists for processing technologies that are capable of cost-effectively producing nanocomposites with high filler concentrations (hence, high thermal and electrical conductivities).

Nanoscale Graphene Plates (NGPs):  Fabrication of carbon nanotubes (CNTs) is expensive, particularly for the purifying process required to make them useful in applications.  Instead of trying to discover lower cost processes for CNTs, we seek to develop an alternative nanoscale carbon material with comparable properties that can be produced cost-effectively and in larger quantities. This development work has led to the discovery of processes for producing a new class of nano material herein referred to as nanoscale graphene plate (NGP, Fig.3).  An NGP is a nanoscale platelet composed of one or more layers of graphene plane. In a graphene plane, carbon atoms occupy a 2-D hexagonal lattice.  These carbon atoms are bonded together through strong covalent bonds lying on this plane. In the c-axis direction, several graphene planes may be weakly bonded together primarily through van der Waals forces. An NGP may be viewed as a flattened sheet of a CNT. Although NGP and CNT are geometrically different in architecture, our preliminary calculations have indicated very similar mechanical properties (in-plane stiffness and strength) and thermal and electrical conductivities.

NGP-based Nanocomposites: NGP-reinforced composites are also expected to exhibit similar properties compared to CNT-reinforced composites. Anticipated features and benefits of NGP nanocomposites include the following:

(1)   In addition to much lower costs, another major advantage of graphene-based nanocomposites is their capability of forming thin films or coatings for electromagnetic interference (EMI) shielding and electrostatic charge dissipation (ESD) applications if the NGP loading exceeds the percolation threshold so that platelets form a network of electron transport paths. We have demonstrated that a high conductivity value can be achieved with a low NGP loading. Due to the high thermal conductivity of NGPs, a nanocomposite thin film or coating can also be used as a thermal management layer in a densely-packed microelectronic device.

(2)   If a high loading of NGPs (15%-85% by wt.) can be incorporated into a polymer or carbon matrix, the resulting nanocomposite could possess an exceptionally high electrical conductivity for fuel cell bipolar plate, battery separator, and battery electrode applications. The feasibility of incorporating a high percentage of NGPs in a polymer matrix to produce highly conductive bipolar plates on a continuous basis has been demonstrated by researchers at NANOTEK.

(3)  NGP nanocomposites have a good combination of mechanical stiffness, strength, micro-cracking resistance, thermal properties and barrier performance at a minimal filler concentration.

(4)   When the NGP nanocomposite is incorporated as a matrix for forming a continuous fiber reinforced composite, the resulting hybrid composite (containing both the NGP and the continuous fiber as reinforcement phases) is expected to have improved mechanical and physical properties compared to the conventional fiber composite (containing only continuous fiber, no NGP). The improved properties include higher transverse strength and stiffness (with the NGP plane being perpendicular to a lamina plane), greater interlaminar shear strength and micro-cracking resistance (and hence, improved delamination resistance, damage tolerance, and fatigue resistance), improved performance temperature, dimensional stability, and both electrical and thermal conductivities.

We have successfully developed several methods of mass-producing nano-scaled graphene plates of several desired size ranges (e.g., length and width of approximately 0.05 to 10 microns and thickness of approximately 1 to 10 nm) using a combination of thermal, chemical and mechanical treatments (patents pending or issued). The resulting NGPs have an average aspect ratio (length/thickness) in the range of approximately 100 to 1000. The obtained NGPs were mixed with a polymer matrix (e.g., epoxy resin and nylon) to prepare NGP-reinforced epoxy and nylon nanocomposites, respectively. Impressive results have been achieved.