Energy harvesting from ocean waves has a high potential and, unlike wind- or solar- energy, wave energy harvesting can be available throughout a year without disruptions. Some of the existing wave energy harvester prototypes are made of steel, and the others are based on polymers, namely, rubbers. The latter ones are light-weight, not prone to corrosion and are expected to require less maintenance at service compared to the steel wave converters. Such rubber-based harvesters are known as dielectric elastomer generators, or DEGs in short, and they are believed to have high potential in the production of the renewable energy. However, being a comparably new technology, electricity produced by DEGs is more expensive than, for example, solar energy. One of the reasons for the high cost is a low efficiency of the current DEGs, meaning that most of the available energy is lost during the transformation of mechanical energy into electricity. Hence, the reduction of the losses should increase the efficiency of such harvesters and, therefore, make DEGs economically feasible.
Despite an active research on the field of rubber-based energy harvesters and the loss reduction efforts, very little attention has been paid to the rubber itself and its losses. For example, the rubber type most often used in DEGs suffer from high mechanical and dielectric losses and have poor mechanical properties.
“Any significant improvement in the efficiency of DEGs is possible only by developing a high performance elastomer – silicone, natural rubber, or other,” believes Alexandra Shakun.
The use of tailor-made high-performance rubber materials is expected to reduce the energy costs down to the cost of solar energy, thus making rubber-based harvesters more attractive.
The present doctoral research is focusing solely on the material-related losses of the selected rubbers, which are expected to be used in DEGs. It is important to understand the contribution of a rubber type, the presence of natural impurities, compounding ingredients and fillers to the losses. For instance, 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 is most probably 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. Therefore, chemical modification of a nanodiamond filler was one important aspect of the study. As a result, the addition of chemically modified nanodiamondss showed a clear reduction of mechanical losses, especially in the silicone composites.
Although the wave energy harvesters are selected as a potential application for the studied rubbers, low-loss rubber films can be used 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 doctoral dissertation of MSc (Tech) Alexandra Shakun in the field of materials science titled Low-Loss Energy Harvesting Materials from Rubber-Nanodiamond Composites will be publicly examined in the Faculty of Engineering and Natural Sciences at Tampere University at 12 o’clock on Tuesday 23.6.2020 in the auditorium FA032 (Pieni sali 1) of the Festia building, Korkeakoulunkatu 8, Tampere. The Opponents will be Professor James Busfield from Queen Mary University of London, United Kingdom, and Professor Dariusz M. Bieliński from Lodz University of Technology, Poland. The Custos will be Assistant Professor Essi Sarlin from the Faculty of Engineering and Natural Sciences, Tampere University, Finland.
Due to the coronavirus situation, the public defence is also available via digital platform.
The dissertation is available online at the http://urn.fi/URN:ISBN:978-952-03-1606-8
Photo: Irina Mironova