Versatile and efficient – CNTs offer enormous potential

BYK carries out basic research in the area of carbon nanotubes (CNTs). Dr. Michael Berkei, Product Group Manager Nanotechnology, in conversation about the new material, and the challenges and enormous potential it offers. 

Dr. Berkei, carbon nanotubes (CNTs) were first discovered at the start of the 1990s and are therefore still a relatively unresearched field. Can you describe for us what kinds of CNTs there are, and where the unique properties of this recent material are to be found? 

Carbon nanotubes can be described as tubes of rolled up sheets of graphene. A distinction is made between single-wall carbon nanotubes, double-wall carbon nanotubes, and multi-wall carbon nanotubes. The carbons are sp2-hybridized and, through their delocalized π-electrons, provide excellent electrical and thermal conductivity – similar to that of metals. Their mechanical strength with a simultaneously very low density also characterizes carbon nanotubes as a unique material. 

The best properties are attributed to the single-wall carbon nanotubes; however, their synthesis is still very elaborate and involves sizeable costs, with the result that the industrial focus is primarily on the significantly cheaper multi-wall carbon nanotubes. 

It is the even distribution of the CNTs and their, in many cases, inadequate bonding with the surrounding matrix that creates significant technological challenges for CNT applications. Where is the difficulty? 

Because of the manufacturing process, carbon nanotubes tend to be present in powder form as strongly entangled agglomerates. This effect is also encouraged by the extremely high aspect ratio of up to 1,000. To make best use of the special properties of the carbon nanotubes, they should be dispersed in the matrix as homogenously as possible. In the case of thermal or electrical conductivity, network formation should also be achieved to facilitate percolation. With applications that rely on mechanical reinforcement by carbon nanotubes, bonding with the matrix is desirable – as practiced today with other fillers. 

Where does the expertise of BYK come into play? Why is it BYK that is carrying out basic research in the area of CNTs? 

To distribute the carbon nanotubes as finely as possible and, at the same time, to keep the aspect ratio as large as possible, special wetting and dispersing additives are required. These additives are tailored to the surface chemistry of the carbon nanotubes and thus facilitate homogenous distribution in the respective matrices. Also, in many cases, it is possible to achieve a bonding of the carbon nanotubes with the surrounding matrix, which will positively affect the mechanical properties. If one were simply to use only high shear forces for the dispersion, the CNT agglomerates would certainly be dissipated – but at the cost of the length of the carbon nanotubes and thus with a loss of the special properties that are associated with a high aspect ratio. 

BYK sees great potential in carbon nanotubes for various applications and, accordingly, has set itself the challenge of developing tailored wetting and dispersing additives for carbon nanotubes and thus making the most of the material.