Adding nanodiamonds to rubber can make energy harvesting more attractive

The energy need is constantly growing, and so does the concern about the climate changes. In recent decades, much research has been focused on the development of the alternative energy technologies and their promotion. One of the solutions allowing to obtain a sustainable fossil-free electricity is energy harvesting from ambient sources. Did you know that rubbers can be used for harvesting energy from the renewable sources, such as waves, pressure, human motion? Such harvesters are light-weight, compact, not prone to corrosion and are expected to require less maintenance at service compared to the steel-based converters. These rubber-based harvesters are known as dielectric elastomer generators, DEGs in short, and they are believed to have high potential in the production of the renewable energy. For instance, energy harvesting from ocean waves can be available throughout a year without disruptions in many places around the globe. However, being a comparably new technology, electricity produced by DEGs is more expensive than, for example, solar energy.

How the energy cost of the DEG harvester can be lowered

One of the reasons for the high energy cost is a low efficiency of the existing DEGs, meaning that most of the available energy is lost during the transformation of mechanical energy into electricity. The reduction of the losses, which are always present in any energy harvesting process, should increase the efficiency of such harvesters and, therefore, make DEGs economically feasible. Surprisingly, very little attention has been paid by the researchers to the rubber and its losses in DEGs. This study aimed to close the knowledge gap and study how different rubber types (natural rubber, silicone, acrylic) and compositions (e.g. addition of nanodiamonds) dissipate mechanical and electric energy and find some simple and affordable methods of lowering material losses. That’s why understanding how a rubber type, the presence of natural impurities, compounding ingredients and fillers contribute to the losses is so crucial. Furthermore, an interesting twist of the research is that rubber composites with low losses are not only expected to increase the attractiveness of the wave energy generators and the renewable energy in general, but also can be applied in other industrial areas. For example, they may enhance the performance of variable capacitors, which are used as stretchable sensors applied in sports garments, biomedical field and robotics. Moreover, tire industry can benefit from the reduced dynamic mechanical losses in rubbers, which can lead to less fuel consumption.

The addition of small amounts of nanodiamonds is viewed as an opportunity of achieving the low-loss rubber

Indeed, dielectric and mechanical losses can be reduced when nanodiamonds are added to silicones. This effect may be related to ability of nanodiamonds to interact with polymer chains. When nanodiamonds are chemically modified, their interaction with the rubber matrix can be adjusted, which results in the change of the losses. That’s why chemical modification of a nanodiamond filler was one important aspect of the study. Among others, an efficient and simple modification reaction was introduced for the nanodiamonds allowing to attach a variety of desirable chemical groups to its surface. As a result, the addition of chemically modified nanodiamonds to the studied rubbers showed a clear reduction of mechanical losses, especially in the silicones. More information is available in the open-access article “Influence of Surface Modified Nanodiamonds on Dielectric and Mechanical Properties of Silicone Composites” in Polymers.

Alexandra Shakun received a half year grant from The Finnish Foundation for Technology Promotion in 2019. She received her PhD from the University of Tampere in 2020.