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Biomimetic Water-Responsive Self-Healing Epoxy with Tunable Properties

Yuan, Dian, Delpierre, Sébastien, Ke, Kai, Raquez, Jean-Marie, Dubois, Philippe, Manas-Zloczower, Ica
ACS applied materials & interfaces 2019 v.11 no.19 pp. 17853-17862
Holothuroidea, adhesion, ambient temperature, biomimetics, crosslinking, electronics, epoxides, health services, humans, mechanical stress, polymers, propylene glycol, rubber, tensile strength
As dynamic cross-linking networks are intrinsically weaker than permanent covalent networks, it is a big challenge to obtain a stiff self-healing polymer using reversible networks. Inspired by the self-healable and mechanically adaptive nature of sea cucumber, we design a water-responsive self-healing polymer system with reversible and permanent covalent networks by cross-linking poly(propylene glycol) with boroxine and epoxy. This double cross-linked structure is self-healing due to the boroxine reversible network as well as showing a room-temperature tensile modulus of 1059 MPa and a tensile stress of 37 MPa, on a par with classic thermosets. The dynamic boroxine bonds provide the self-healing response and enable up to 80% recovery in modulus and tensile strength upon water contact. The system shows superior adhesion to metal substrates by comparison with the commercial epoxy-based structural adhesive. Besides, this system can change modulus from a stiff thermoset to soft rubber (by a factor of 150) upon water stimulus, enabling potential applications of either direct or transform printing for micro/nanofabrication. Moreover, by incorporating conductive nanofillers, it becomes feasible to fabricate self-healing and versatile strain/stress sensors based on a single thermoset, with potential applications in wearable electronics for human healthcare.