Unidirectional freeze casting of compressible metallic aerogel composed of freeze-dried cellulose nanofibers and silver nanowires

Abstract

Metallic aerogels have attracted tremendous interest because of their superior properties, such as low density, high electrical conductivity, and large specific surface area. However, extremely brittle connections in their 3D networks remain a challenge. In this study, compressible aerogels with microporous fiber-like structure consisting of freeze-dried cellulose nanofibers (CNFs) and silver nanowires (AgNWs) were fabricated by unidirectional freeze-casting process. To improve the robustness, elasticity, and deformability of the aerogel, freeze-dried microfiber-structured CNFs assembled with AgNWs were used. The freeze-dried CNF/AgNW-based aerogels exhibited a low density (8.51–13.5 mg/cm³) and high porosity (up to 98.2%). Furthermore, these aerogels demonstrated impressive mechanical properties with high compressive strength (up to 4.85 kPa at 70% strain), elastic modulus (up to 16.3 kPa), and yield strength (up to 2 kPa). Additionally, the aerogels exhibited reversible deformability up to a 10% strain and maintained their durability over 200 cycles of compressive strain at 10%. The fabricated aerogels also showed a low electrical resistivity (< 8.65 mΩ·m) in addition to robust and compressible mechanical properties. These aerogels are expected to be useful in a wide range of applications that require characteristics such as light weight, high compressive strength, high elasticity, and low electrical resistivity.