Synergic enhancement of hydrogel upon multi-level hydrogen bonds via macromolecular design for dual-mode electronic skin

Acrylamide (AM) derivative polymer hydrogels were widely used due to their excellent mechanical performances and the ease to be further functionalized, while there are significant differences in both microstructure and performances along with the variation of substituent groups. So far, the intrinsic reason for this is never revealed. In this paper, double network hydrogels with three AM derivative monomers as the first polymer network: AM, N,N-dimethylacrylamide (DMAA) and N-hydroxymethylacrylamide (NMA), and methyl cellulose (MC) as the second network, were prepared. Compared with PAM based hydrogel, the elasticity and toughness of PDMAA based hydrogel increased by two times. The results from molecular dynamics simulation, FT-IR and XRD demonstrate that intermolecular force among polymer networks in hydrogels increased with AM derivative polymers achieved from primary amine to tertiary amine (DMAA), stemmed from the variation of substituent groups on N atom of AM derivative monomers. The PDMAA based hydrogel was finally employed to construct a dual-mode electronic skin, in a wearable sensor with the fastest response of 0.1 s and a self-powered device with a capacitance of 438.27 mF/cm2. This work provided an in-depth understanding for the optimization of PAM based hydrogels and a novel way for the construction of flexible devices.