Extremely low thermal conductivity and high electrical conductivity of sustainable carbon-ceramic electrospun nonwoven materials.

Materials with an extremely low thermal and high electrical conductivity that are easy to process, foldable, and nonflammable are required for sustainable applications, notably in energy converters, miniaturized electronics, and high-temperature fuel cells. Given the inherent correlation between high thermal and high electrical conductivity, innovative design concepts that decouple phonon and electron transport are necessary. We achieved this unique combination of thermal conductivity 19.8 ± 7.8 mW/m/K (cross-plane) and 31.8 ± 11.8 mW/m/K (in-plane); electrical conductivity 4.2 S/cm in-plane in electrospun nonwovens comprising carbon as the matrix and silicon-based ceramics as nano-sized inclusions with a sea-island nanostructure. The carbon phase modulates electronic transport for high electrical conductivity, and the ceramic phase induces phonon scattering for low thermal conductivity by excessive boundary scattering. Our strategy can be used to fabricate the unique nonwoven materials for real-world applications and will inspire the design of materials made from carbon and ceramic.

Ultralight, Structurally Stable Electrospun Sponges with Tailored Hydrophilicity as a Novel Material Platform.

Sponges based on short electrospun fibers have received significant attention due to their ultrahigh porosity, lightweight, and multifunctional characteristics. In particular, polyimide (PI) sponges have been researched due to their exceptional mechanical properties and thermal stability. Nevertheless, a number of sponges, including PI, are usually hydrophobic and synthesized in toxic, nonwater solvents (e.g., 1,4-dioxane). Conversely, hydrophilic sponges disintegrate upon contact with water. Here, we suggest a new strategy to fabricate PI sponges in water by introducing a suitable surfactant, sodium dodecylbenzenesulfonate (SDBS) (sPI sponges). With less than 1 wt % of SDBS with respect to PI short fibers, they can be homogeneously dispersed in water and mixed well with poly(amic acid) (PAA) solution. The synthesized sponge, depending on the concentration of SDBS, showed hydrophilic properties and substantial water uptake above 5000%. The hydrophilic properties of the sponges, which are not common, and the preparation from aqueous solution introduce new research opportunities. Such hydrophilic sponges are particularly special because they do not swell in contact with water, which makes them dimensionally stable. The methods presented here can serve as a milestone for the future development of various kinds of hydrophilic sponges applied for various applications, ranging from tissue engineering to oil/water separation.