Researchers at the University of Bayreuth (Germany; www.uni-bayreuth.de) have developed nonwoven materials that exhibit an unusual combination of high electrical conductivity and extremely low thermal conductivity. These composites of carbon and silicon-based ceramic can be manufactured and processed cost-effectively by an electrospinning process, and have potential for applications in energy management, battery-powered electromobility, smart textiles or aerospace.
Normally, high electrical conductivity is associated with high thermal conductivity, and vise versa. However, there is growing interest in multifunctional materials that combine good electrical conductivity with low thermal transport. Although several strategies have been developed in materials such as 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.
As described in a recent issue of Science Advances, the new electrospun nonwovens (photos) consist of fibers with a diameter between 500 and 600 nm. Each fiber 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 properties. The carbon matrix enables the electron transport in the fibers and thus high electrical conductivity, while the nano-sized silicon-based ceramic prevent thermal energy from spreading. This is because the interface between the nano-sized ceramic and the carbon matrix is very large, while the pores of the nonwoven are very small. As a result, there is a strong scattering of phonons — the smallest physical units of vibrations triggered by thermal energy — and thus a continuous, directed-heat flow does not occur.
In comparison with more than 3,900 different materials (ceramics, carbons, natural materials, synthetic polymers, metals, glasses and various composite materials), the electron transport and thermal insulation was more coupled with the new nonwovens.
Bayreuth scientists from different research centers collaborated in the development of the new material and the necessary preliminary studies: the Bavarian Polymer Institute (BPI), the Bayreuth Center for Colloids and Interfaces (BZKG), the Bavarian Geoinstitute (BGI) and the Bavarian Center for Battery Technology (BayBatt).