No abstract

Stretchable ionic conductors such as hydrogels and ionic‐liquid‐based gels (aka ionogels) have garnered great attention as they enable the development of soft ionotronics. Notably, soft ionotronic devices inevitably operate in humid environments or under mechanical loads. However, many previously reported hydrogels and ionogels, however, are unstable in environments with varying humidity levels owing to hydrophilicity, and their liquid components (i.e., ionic liquid, water) may leak easily from polymer matrices under mechanical loads, causing deterioration of device performance. This work presents novel hydrophobic ionogels with strong ionic liquid retention capability. The ionogels are ambiently and mechanically stable, capable of not absorbing moisture in environments with high relative humidity and almost not losing liquid components during long periods of mechanical loading. Moreover, the ionogels exhibit desirable conductivity (10−4–10−5 S cm−1), large rupturing strain (>2000%), moderate fractocohesive length (0.51–1.03 mm), and wide working temperature range (−60 to 200 °C). An ionic skin is further designed by integrating the concept of sensory artificial skins and triboelectric nanogenerators, which can convert multiple stimuli into various types of signals, including resistance, capacitance, short‐circuit current, and open‐circuit voltage. This work may open new avenues for the development of soft ionotronics with stable performance.

High strength, toughness, and conductivity are among the most sought‐after properties of flexible electronics. However, existing engineering materials find it difficult to achieve both excellent mechanical properties and high conductivity. To address this challenge, this study proposes a facile yet versatile strategy for preparing super‐tough conductive organo‐hydrogels via freeze‐casting assisted solution substitution (FASS). This FASS strategy enables the formation of organo‐hydrogels in one step with exquisite hierarchical anisotropic structures coupled with synergistic strengthening and toughening effects across multiple length scales. As an exemplary material, the prepared polyvinyl alcohol (PVA) organo‐hydrogel with solvent content up to 87 wt% exhibits a combination of high strength (6.5 MPa), high stretchability (1710% in strain), ultra‐high toughness (58.9 MJ m−3), as well as high ionic conductivity up to 6.5 S m−1 with excellent strain sensitivity. The exceptional combination of mechanical properties and conductivity makes the PVA organo‐hydrogel a promising flexible electronics material. In addition, the FASS strategy can also endow hydrogels with multi‐functions, including thermo‐healability, freezing tolerance and shape recoverability, and can be applied to various hydrogel materials, such as carboxymethyl cellulose, sodium alginate, and chitosan. Hence, this work provides an all‐around solution for preparing advanced strong and tough conductive soft materials for a multitude of applications.

Tough natural materials such as nacre, bone, and silk exhibit multiscale hierarchical structures where distinct toughening mechanisms occur at each level of the hierarchy, ranging from molecular uncoiling to microscale fibrillar sliding to macroscale crack deflection. An open question is whether and how the multiscale design motifs of natural materials can be translated to the development of next-generation biomimetic hydrogels. To address this challenge, we fabricate strong and tough hydrogel with architected multiscale hierarchical structures using a freeze-casting–assisted solution substitution strategy. The underlying multiscale multimechanisms are attributed to the gel’s hierarchical structures, including microscale anisotropic honeycomb–structured fiber walls and matrix, with a modulus of 8.96 and 0.73 MPa, respectively; hydrogen bond–enhanced fibers with nanocrystalline domains; and cross-linked strong polyvinyl alcohol chains with chain-connecting ionic bonds. This study establishes a blueprint of structure-performance mechanisms in tough hierarchically structured hydrogels and can inspire advanced design strategies for other promising hierarchical materials.

No abstract