High-Saline-Enabled Hydrophobic Homogeneous Cross-Linking for Extremely Soft, Tough, and Stretchable Conductive Hydrogels as High-Sensitive Strain Sensors.

Design of admirable conductive hydrogels combining robust toughness, soft flexibility, desirable conductivity, and freezing resistance remains daunting challenges for meeting the customized and critical demands of flexible and wearable electronics. Herein, a promising and facile strategy to prepare hydrogels tailored to these anticipated demands is proposed, which is prepared in one step by homogeneous cross-linking of acrylamide using hydrophobic divinylbenzene stabilized by micelles under saturated high-saline solutions. The influence of high-saline environments on the hydrogel topology and mechanical performance is investigated. The high-saline environments suppress the size of hydrophobic cross-linkers in micelles during hydrogel polymerization, which weaken the dynamic hydrophobic associations to soften the hydrogels. Nevertheless, the homogeneous cross-linked networks ensure antifracture during ultralarge deformations. The obtained hydrogels show special mechanical performance combining extremely soft deformability and antifracture features (Young's modulus, 5 kPa; stretchability, 10200%; toughness, 134 kJ m-2; and excellent anticrack propagation). The saturated-saline environments also endow the hydrogels with desirable ion conductivity (106 mS cm-1) and freezing resistance (<20 °C). These comprehensive properties of the obtained hydrogels are quite suitable for flexible electronic applications, which is demonstrated by the high sensitivity and durability of the derived strain sensors.

An Anti-Fracture and Super Deformable Soft Hydrogel Network Insensitive to Extremely Harsh Environments.

Design of hydrogels with superior flexible deformability, anti-fracture toughness, and reliable environment adaption is fundamentally and practically important for diverse hydrogel-based flexible devices. However, these features can hardly be compatible even in elaborately designed hydrogels. Herein soft hydrogel networks with superior anti-fracture and deformability are proposed, which show good adaption to extremely harsh saline or alkaline environments. The hydrogel network is one-step constructed via hydrophobic homogenous cross-linking of poly (sodium acrylate), which is expected to provide hydrophobic associations and homogeneous cross-linking for energy dissipation. The obtained hydrogels are quite soft and deformable (tensile modulus: ≈20 kPa, stretchability: 3700%), but show excellent anti-fracture toughness (10.6 kJ m-2 ). The energy dissipation mechanism can be further intensified under saline or alkaline environments. The mechanical performance of the hydrophobic cross-linking topology is inspired rather than weakened by extremely saline or alkaline environments (stretchability: 3900% and 5100%, toughness: 16.1 and 17.1 kJ m-2 under saturated NaCl and 6 mol L-1 NaOH environments, respectively). The hydrogel network also shows good performance in reversible deformations, ion conductivity, sensing strain, monitoring human motions, and freezing resistance under high-saline environments. The hydrogel network show unique mechanical performance and robust environment adaption, which is quite promising for diverse applications.