Instant-healing double-network polydimethylsiloxane with low stiffness and high toughness

The double-network mechanism is a key advance that has led to soft and tough materials. Solvent-swollen double-network materials containing a dynamic network have exhibited additional fast healing functionality. However, achieving similar performance in solvent-free materials is a challenge. This work develops a tough and soft double-network polydimethylsiloxane (DN-PDMS) material that instantly heals in seconds. The DN-PDMS comprises a bottlebrush network and a dynamic borate PDMS. The DN-PDMS with an equal weight of each network demonstrates high fracture toughness of 3.8kJ/m2, high failure strain of 15, and flaw-insensitivity to a centimeter-long notch. When the material is cut and brought back in contact, 40% of the initial toughness and 50% of the initial failure strain are recovered in ten seconds at room temperature. The dynamic mechanical analysis demonstrates fast kinetics of physical interactions in the timescale of seconds, enabling fast healing. We anticipate that this development paves a path to designing soft materials that can bear repeated mechanical loads.