Sturdy and conductive polyacrylamide/sodium alginate dual-network hydrogels improved via refreezing assisted metal...

The rapid growth of flexible hydrogels provides a fresh way forward for wearable electronics. However, insufficient mechanical strength and low conductivity still hinder their further applications. This work puts forward a simple and efficient refreezing assisted metal complexation (RAMC) strategy to synergistically enhance the mechanical and electrochemical properties of the metal-based polyacrylamide/sodium alginate (PAM/SA) dual-network hydrogels. Through RAMC strategy, the free water is removed in form of an ice shell, and the functional groups on the chain form multiple can coordinate with the transition metal (Cu, Zn, Fe, Co, and Ni), which increases the strength of the network. The resultant F₂-0.50Cu/PAM/SA hydrogels exhibit mechanical tensile strength of 2.201 MPa and high stretchability of nearly 250 %, showing a notable improvement compared to the PAM/SA hydrogels. Concurrently, the transition metal exerted an important influence on the conductivity of the hydrogel, so that the ionic conductivity of the 0.50Ni/PAM/SA hydrogels with sensing properties reached 134.11 mS cm^-1. In addition, the density functional theory (DFT) calculations and LAMMPS simulations are employed to elucidate the interactions and changes of components in the hydrogel systems towards the observed alterations of mechanical properties. Further, some targeted human movements are designed to describe the different graphic signals of hydrogels in response to different deformations, demonstrating the high potential in wearable applications.