Development of an Ultrastretchable Double-Network Hydrogel for Flexible Strain Sensors
Huijun Li, Han Zheng, Yu Jun Tan, Shu Beng Tor, Kun Zhou
Abstract
The weak mechanical properties of hydrogels due to the inefficient dissipation of energy in the intrinsic structures limit their practical applications. Here, a double-network (DN) hydrogel has been developed by integrating an ionically cross-linked agar network, a covalently cross-linked acrylic acid (AAC) network, and the dynamic and reversible ionically cross-linked coordination between the AAC chains and Fe3+ ions. The proposed model reveals the mechanisms of the improved mechanical performances in the DN agar/AAC–Fe3+ hydrogel. The hydrogen-bond cross-linked double helices of agar and ionic-coordination interactions of AAC–Fe3+ can be temporarily sacrificed during large deformation to readily dissipate the energy, whereas the reversible AAC–Fe3+ interactions can be regenerated after stress relief, which greatly increases the material toughness. The developed DN hydrogel demonstrates a remarkable stretchability with a break strain up to 3174.3%, high strain sensitivity with the gauge factor being 0.83 under a strain of 1000%, and good 3D printability, making the material a desirable candidate for fabricating flexible strain sensors, electronic skin, and soft robots.