Building Carbon Nanotubes with Ceramic Scaffolding
Scientists from Kiel University and the University of Trento are using ceramic scaffolding in the development of new composite material made of carbon nanotubes.
Extremely lightweight, electrically highly conductive and more stable than steel: due to their unique properties, carbon nanotubes (CNTs) would be ideal for applications ranging from ultra-lightweight batteries to high-performance plastics and medical implants. However, it has been difficult for science and industry to transfer CNTs’ extraordinary characteristics at the nano-scale into a functional industrial application. The CNTs either cannot be combined adequately with other materials, or if they can be combined, they then lose their beneficial properties.
Scientists from the Functional Nanomaterials working group at Kiel University (CAU) and the University of Trento have developed an alternative method, with which the tiny tubes can be combined with other materials so that they retain their characteristic properties. As such, they “felt” the thread-like tubes into a stable 3D network that is able to withstand extreme forces. The research results have been published in Nature Communications.1
Zinc Oxide Scaffolding
Industry and science have been intensively researching the significantly less than 100-nm-wide CNTs in order to make use of the extraordinary properties of rolled graphene. Yet much still remains simply theory.
“Although carbon nanotubes are flexible like fiber strands, they are also very sensitive to changes,” said Professor Rainer Adelung, head of the Functional Nanomaterials working group at the CAU. “With previous attempts to chemically connect them with other materials, their molecular structure also changed. This, however, made their properties deteriorate—mostly drastically.”
In contrast, the approach of the research team from Kiel and Trento is based on a simple wet chemical infiltration process. The CNTs are mixed with water and dripped into an extremely porous ceramic material made of zinc oxide, which absorbs the liquid like a sponge. The dripped thread-like CNTs attach themselves to the ceramic scaffolding and automatically form a stable layer together, similar to a felt. The ceramic scaffolding is coated with nanotubes, so to speak, resulting in fascinating effects for both the scaffolding and the coating of nanotubes.
On the one hand, the stability of the ceramic scaffold increases so massively that it can bear 100,000 times its own weight. “With the CNT coating, the ceramic material can hold around 7.5 kg, and without it just 50 g—as if we had fitted it with a close-fitting pullover made of carbon nanotubes, which provide mechanical support,” said Fabian Schütt, lead author. “The pressure on the material is absorbed by the tensile strength of the CNT felt. Compressive forces are transformed into tensile forces.”
The principle behind this is comparable to bamboo buildings, such as those that are widespread in Asia. Here, bamboo stems are bound so tightly with a simple rope that the lightweight material can form extremely stable scaffolding, and even entire buildings. “We do the same at the nano-scale with the CNT threads, which wrap themselves around the ceramic material—only much, much smaller,” said Helge Krüger, co-author.
The materials scientists were able to demonstrate another major advantage of their process. In a second step, they dissolved the ceramic scaffolding using a chemical etching process. The remaining fine 3D network of tubes each consists of a layer of tiny CNT tubes. In this way, the researchers were able to greatly increase the felt surface and thus create more opportunities for reactions.
“We basically pack the surface of an entire beach volleyball field into a 1-cm cube,” said Schütt. The huge hollow spaces inside the three-dimensional structure can then be filled with a polymer. As such, CNTs can be connected mechanically with plastics, without their molecular structure (and thus their properties) being modified.
“We can specifically arrange the CNTs and manufacture an electrically conductive composite material,” said Schütt. “To do so only requires a fraction of the usual quantity of CNTs in order to achieve the same conductivity.”
Simple Procedure for Many Applications
Potential applications range from battery and filter technology as a filling material for conductive plastics to implants for regenerative medicine and sensors and electronic components at the nano-scale. The good electrical conductivity of the tear-resistant material could also be interesting for future flexible electronics applications, in functional clothing or in the field of medical technology.
“Creating a plastic which, for example, stimulates bone or heart cells to grow is conceivable,” said Adelung. Due to its simplicity, the scientists agree that the process could also be transferred to network structures made of other nanomaterials, which will further expand the range of possible applications.
This work was supported by the German Research Foundation (DFG) and the European Commission in the framework of the Graphene FET Flagship project. For more information, visit www.uni-kiel.de.
1. Schütt, Fabian; Signetti, Stefano; Krüger, Helge; Röder, Sarah; Smazna, Daria; Kaps, Sören; Gorb, Stanislav N.; Kumar Mishra, Yogendra; Pugno Nicola M.; and Adelung, Rainer, “Hierarchical Self-Entangled Carbon Nanotube Tube Networks,” Nature Communications, 8, 1215 (2017),