In Last week’s post we discussed the many forms in which carbon nanotubes (CNTs) can be incorporated into commercial products. In addition to starting with a high quality source of raw CNT materials, we emphasized that we can best optimize the potential of CNTs by aligning them into fibers/films and use these formats further to construct advanced 3D structures. DexMat's process maintains the high strength, electrical/ thermal conductivity, and low density of the CNT’s to create new opportunities in high-performance applications. In this post, we explore some CNT applications that require superior CNT material performance, including applications in biomedical, resource manufacturing, aerospace, industrial goods, and electrical energy storage and distribution sectors.
Biomedical Applications
Biomedical engineering is a perfect example of an area in which multifunctional materials, such as aligned CNT fibers and films, vertically aligned arrays, and 3D scaffolds, can lead to new applications that might not have been possible with conventional materials. Solid CNT materials tend to have very high surface area (since they are made from many thin overlapping cylinders with micro- or nano-scale pores between them) and therefore have low electrochemical impedance; that is, they can form a good electrical connection with electrolytic fluids, such as saline or other fluids in the body. The low electrochemical impedance of CNT materials, coupled with the fact that they can be soft, flexible, and durable, makes them useful as electrodes which can be implanted in the body. In terms of pure available surface area, low-density CNT structures such as vertically aligned arrays have an edge over very highly aligned and well-packed CNT structures; the latter are still filled with nano-scale pores, but these may be difficult for electrolyte fluids to access if the CNTs are slightly hydrophobic. However, highly aligned CNT structures have an edge in terms of mechanical strength and durability, and they still have surface areas, flexibility, and flexural tolerances far greater than those of metal electrodes. Well-packed CNT structures, held together by strong van der Waals forces, are also less likely to allow CNTs to shed from their surfaces or break apart from one another compared to low-density arrays or disordered mats. For all of these reasons, aligned CNT structures have great potential to one day be commercialized as durable medical electrodes, either for implantation in the body or for “dry” contact with the skin. CNT electrodes combined with smart clothing can potentially be used to make wearable sensors that monitor health data continuously.
Air & Water Purification
Carbon nanotubes (CNTs) have a combination of properties that make them quite useful for air and water filtration. Their cylindrical structure and strong carbon-carbon bonds make them stiff and durable, which allows them to form stable overlapping networks with extremely high porosity and surface area, perfect for the construction of filter materials. The electrical conductivity of CNT networks also allows them to be used for active filtration, which cannot be achieved with glass, plastic, or paper filters. It is possible that the further development of CNT filters might lead to advances in the flexibility, portability, and longevity of air and water purification devices; we detail the challenges and needs of air filtration and water filtration devices in these past blog posts.
Aerospace & Transportation
The strength, electrical conductivity, and low density of aligned CNT materials make them ideal for electronics applications in which weight reduction is a priority. Compared to a copper wire or sheet with similar dimensions, a DexMat CNT fiber or film has 6 times the strength, at least 25 times higher flexure tolerance, and only 1/6 the density, all of which are essential qualities for conductive wires in aerospace applications. Shielding sensitive electronic equipment from electromagnetic interference requires metallic layers that add significant weight to aircraft or spacecraft; aligned CNT products such as fibers and films are a promising solution for reducing the weight of EMI shielding without sacrificing current standards. One of our past blog posts has information about prototype data cables we have made with this application in mind. These assembled cables provided a 50% weight reduction and a decrease in diameter compared to state-of-the-art cables with comparable shielding power. We have found that application of CNT film onto wires as a shielding layer can also be faster than the process of manufacturing braided copper shielding procedures, and our finished cable was able to survive 1000’s of flex cycles due to the increased flexibility and overall cable diameter reduction.
Consumer and Industrial Goods
DexMat CNT yarn is conductive, durable, flexible, and lightweight, which makes it a perfect fit for the emerging field of wearable electronics. Because CNT yarn can be handled like a textile thread, it can potentially be combined together with conventional yarns to make clothing that has complex electronic functionality without sacrificing comfort or weight; at the same time, CNT yarn has a conductivity that is similar to metals, exceeding that of stainless steel thread (one of the primary materials used for high conductivity wearable electronics). More information on typical e-textile yarns is available here. CNT yarn is also more resistant to oxidation than stainless steel, so it should maintain its properties and durability through laundering and daily use. CNT yarns might be used to create wearable devices that range from heating elements in clothing, to power generation and feedback for our mobile devices, to wearable skin contacting monitors to keep track of our health and wellness.
CNT yarns can also be woven into a standalone cloth or fabric, such as the prototype shown above. This woven fabric can take the place of durable clothing fabrics, with the added benefit of electronic interfacing. A material of this kind might be used to add capacitive touch sensing pads, like the one demonstrated here; this could be used to fabricate clothing with built-in buttons or even keyboards which operate with the touch of a finger. Other applications might exploit the purely mechanical properties of aligned CNT yarn fabric, such as cut resistant gloves and lightweight, flexible bulletproof clothing.
Electrical Energy Production and Distribution
Aligned CNT fibers and yarns are gaining the attention of the electric motor and power generation industries since they offer a flexible, strong, and lightweight option for motor and generator winding constructions (see article here). The flexibility of CNT fibers is vastly superior to metallic conductors such as copper, and is more comparable to that of a textile thread with the ability to survive millions of flex cycles. Combined with its high strength, this level of flexibility can allow for an increase in packing efficiency of motor windings and enable faster, more reliable installation methods to create improved magnet wire constructions. CNT fibers and yarns are also by far the lightest option for motor and generator winding options. If the conductivity of CNT yarns can be increased further through technology and process improvements, then this material may be the next big innovation in magnet wire for lightweight, highly efficient motors and generators.
Limitations
One of the primary drawbacks to using highly aligned CNT yarns and films is the cost of the finished material; these fibers are currently one of the higher priced alternatives to similar solutions. We will devote an entire blog post to the topic of CNT material costs in the future. In short, this cost is partly due to the effort required to process raw CNTs into a highly ordered state, and partly due to the cost of the high-quality and high-purity CNTs that are required for that process to work. Fortunately, the production volume of high-quality CNTs continues to increase in response to the demand for CNT materials in various applications. As advances in production techniques evolve, the cost of carbon nanotubes fibers and films will start to come down considerably, and these extraordinary materials will be viable for a wide plethora of commercial applications.