Highly stretchable porous composite hydrogels with stable conductivity for strain sensing

Stretchable hydrogels have undergone a rapid development in recent years particularly for wearable strain sensors. However, most of hydrogel-based sensors exhibit poor mechanical properties. Here, we report a highly stretchable porous composite hydrogel that has a tensile strain of 400% and a compressive strain of 80%. The porous hydrogel is composed of polyvinyl alcohol (PVA) and copolymer of N-(3-sulfopropyl)-N-methacroyloxyethyl-N,N-dimethylammonium betaine (SBMA) and acrylamide (AM) prepared via graphene oxide (GO)-stabilized Pickering aqueous foam templates. The pore morphology of the composite hydrogels was observed by field emission scanning electron microscope (FE-SEM). The tensile and compressive curves of porous hydrogels with different GO concentrations were characterized. GO can act as Pickering stabilizer to produce aqueous foams and also construct the physical cross-linking network in porous hydrogels to improve their mechanical strength. In addition, when GO is reduced by L-ascorbic acid, it provides effective electric pathways in porous hydrogels with the conductive percolation of less than 0.40 wt%. The composite hydrogels thus exhibit excellent strain sensitivity and can be used to detect various human motions. The facile preparation process of the porous composite hydrogels with outstanding performance properties facilitates the development of flexible wearable strain sensing materials.