Soft double-network polydimethylsiloxane: fast healing of fracture toughness

Abstract

Solvent-swollen double-network materials containing one dynamic network and one permanent network offer softness, toughness, and fast-healing functionality. However, achieving these multiple functionalities in solvent-free materials remains a challenge. Herein, we develop a soft, solvent-free, double-network polydimethylsiloxane (DN-PDMS) material. A covalent bottlebrush network with low crosslink/entanglement densities provides ultralow stiffness. A dynamic borate network dissipates energy to toughen the material and self-heals to recover toughness from damages/pre-cuts. The high mobility of bottlebrush architecture and fast bond-reforming kinetics of borate network provide fast self-healing without stimuli. A DN-PDMS with an equal weight of each network demonstrates a fracture toughness of 3.8 kJ m⁻² and a failure strain of 15. When cut materials are brought into contact for 10 seconds, the material recovers to a toughness of 1.5 kJ m⁻² and a failure strain of 7. The fast-healing DN-PDMS with softness and toughness offers a significant advance by providing toughness and healing without a solvent.