Dense Hydrogen-Bonding Network Boosts Ionic Conductive Hydrogels with Extremely High Toughness, Rapid Self-Recovery, and Autonomous Adhesion for Human-Motion Detection

The construction of ionic conductive hydrogels with high transparency, excellent mechanical robustness, high toughness, and rapid self-recovery is highly desired yet challenging. Herein, a hydrogen-bonding network densification strategy is presented for preparing a highly stretchable and transparent poly(ionic liquid) hydrogel (PAM-r-MVIC) from the perspective of random copolymerization of 1-methyl-3-(4-vinylbenzyl) imidazolium chloride and acrylamide in water. Ascribing to the formation of a dense hydrogen-bonding network, the resultant PAM-r-MVIC exhibited an intrinsically high stretchability (>1000%) and compressibility (90%), fast self-recovery with high toughness (2950 kJ m⁻³), and excellent fatigue resistance with no deviation for 100 cycles. Dissipative particle dynamics simulations revealed that the orientation of hydrogen bonds along the stretching direction boosted mechanical strength and toughness, which were further proved by the restriction of molecular chain movements ascribing to the formation of a dense hydrogen-bonding network from mean square displacement calculations. Combining with high ionic conductivity over a wide temperature range and autonomous adhesion on various surfaces with tailored adhesive strength, the PAM-r-MVIC can readily work as a highly stretchable and healable ionic conductor for a capacitive/resistive bimodal sensor with self-adhesion, high sensitivity, excellent linearity, and great durability. This study might provide a new path of designing and fabricating ionic conductive hydrogels with high mechanical elasticity, high toughness, and excellent fatigue resilience for skin-inspired ionic sensors in detecting complex human motions.

Viscoelasticity of Nanosheet-Filled Polymer Composites: Three Regimes in the Enhancement of Moduli

We employed nonequilibrium molecular dynamics simulations to elucidate the viscoelastic properties of nanosheet (NS)-filled polymer composites. The effects of NS loadings and NS-polymer interaction on viscoelasticity were examined. The simulation results show that the NS-filled polymer composites exhibit an enhanced storage modulus and loss modulus as the NSs are loaded. There are three regimes of the enhanced process based on the NS loadings. At lower NS loadings, the motion of polymers slows down owing to the interaction between NSs and polymers, and the polymer chains generally follow the Rouse dynamics. As the NS loadings increase, the polymer chains are confined between NSs, leading to a substantial increment in dynamic moduli. At higher NS loadings, a transient network is formed, which strengthens the dynamic moduli further. In addition, the attractive NS-polymer interaction can improve the dispersion of NSs and increase the storage and loss moduli. The present work could provide essential information for designing high-performance hybrid polymeric materials.