Thermally insulating and electroactive cellular nanocellulose composite cryogels from hybrid nanofiber networks

Cellulose-based xerogels, cryogels and aerogels have been proposed to deliver the functions required by next-generation wearable electronics and energy materials. However, such systems often lack functionality and present limited mechanical resilience. Herein, we introduce a simple strategy to synthesize high-performance cryogels that combine cellulose and silica nanofibers that form ice-templated cellular architectures. Specifically, dual networks are produced by incorporating organic (cellulose) and inorganic (silica) nanofibers to form highly interconnected and vertically-aligned channels. Hence, ultralight structures (7.37 mg cm−3 in density and porosity of 99.37%) are produced with high mechanical strength, compressibility (dimensional recovery of up to 90%) and fatigue resistance (1000 loading cycles) along with low thermal conductivity (29.65 mW m−1K−1). Electrical responsiveness is supplemented by in situ polymerization of pyrrole, ensuing operation in a wide load range (0–18 kPa with sensitivity of 6.63 kPa−1 during > 1000 cycles). The obtained thermal insulating and electroactive materials are demonstrated for operation under extreme conditions (solvent and temperature). Overall, our dual network system provides a universal, multifunctional platform that can substitute state-of-the-art carbonized or carbon-based light-weight materials.