Researchers in Germany have developed novel electrospun nonwovens that exhibit an unusual combination of high electrical conductivity and extremely low thermal conductivity.
- The nonwovens represent a breakthrough in materials research: it has been possible to decouple electrical and thermal conductivity based on a simple-to-implement material concept.
- The nonwovens are made of carbon and silicon-based ceramic via electrospinning process and are attractive for technological applications, for example, in energy technology and electronics.
- These can be manufactured and processed cost-effectively on an industrial scale.
The Research: University of Bayreuth scientists from different research centres collaborated in the development of the new material and the necessary preliminary studies.
- The centres were the Bavarian Polymer Institute (BPI), the Bayreuth Center for Colloids and Interfaces (BZKG), the Bavarian Research Institute of Experimental Geochemistry & Geophysics (BGI), and the Bavarian Center for Battery Technology (BayBatt).
- The research was funded by the German Research Foundation (DFG) as part of a joint research project between the Chair of Ceramic Materials Engineering and the Chair of Macromolecular Chemistry II.
The Science: Normally, high electrical conductivity is associated with high thermal conductivity, and low thermal conductivity goes with low electrical conductivity. However, in many high-tech industries, there is growing interest in multifunctional materials that that combine good electric with low thermal transport.
- Though several strategies have been developed in the materials, like dense inorganic materials, conjugated polymers, and alloys, achieving extremely low thermal conductivity in combination with high electrical conductivity is still a major challenge for flexible, foldable materials.
- The research team at the University of Bayreuth has discovered an innovative concept to address this challenge: new electrospun nonwovens are made of carbon and silicon based ceramic and consist of fibres with a sea-island type nanostructure and with a diameter between 500 and 600 nanometers.
- Every fibre contains a matrix of carbon in which nano-sized ceramic phases are homogeneously distributed. The particles form tiny "islands" in the "sea" of carbon matrix and have opposite, complementary effects.
- The carbon matrix enables the electron transport in the fibres and thus high electrical conductivity, meanwhile the nano-sized silicon-based ceramic, prevent thermal energy from spreading just as easily.
- This is because the interface between the nano-sized ceramic and the carbon matrix is very high, while the pores of the nonwoven are very small.
- As a result, there is a strong scattering of phonons, which is the smallest physical units of vibrations triggered by thermal energy. A continuous directed heat flow does not occur.
- The unusual combination of high electrical and extremely low thermal conductivity now is highlighted by a comparison with more than 3,900 materials of all types, including ceramics, carbons, natural materials, synthetic polymers, metals, glasses, and various composites.
What They Said:
Our electrospun nonwovens combine highly attractive multifunctional properties that are usually distributed among different classes of materials: high electrical conductivity, thermal insulation familiar from polymer foams, and non-flammability and heat resistance characteristic of ceramics. The fibres are based on a simple material concept, and they were made from commercial polymers.
— Dr Xiaojian Liao (first author)
Postdoctoral researcher, macromolecular chemistry
University of Bayreuth
