Soft ionic conductors, such as hydrogels and ionogels, have enabled stretchable and transparent ionotronics, but they suffer from key limitations inherent to the liquid components, which may leak and evaporate. Here, novel liquid‐free ionic conductive elastomers (ICE) that are copolymer networks hosting lithium cations and associated anions via lithium bonds and hydrogen bonds are demonstrated, such that they are intrinsically immune from leakage and evaporation. The ICEs show extraordinary mechanical versatility including excellent stretchability, high strength and toughness, self‐healing, quick self‐recovery, and 3D‐printability. More intriguingly, the ICEs can defeat the conflict of strength versus toughness—a compromise well recognized in mechanics and material science—and simultaneously overcome the conflict between ionic conductivity and mechanical properties, which is common for ionogels. Several liquid‐free ionotronics based on the ICE are further developed, including resistive force sensors, multifunctional ionic skins, and triboelectric nanogenerators (TENGs), which are not subject to limitations of previous gel‐based devices, such as leakage, evaporation, and weak hydrogel–elastomer interfaces. Also, the 3D printability of the ICEs is demonstrated by printing a series of structures with fine features. The findings offer promise for a variety of ionotronics requiring environmental stability and durability.
Novel liquid‐free ionic conductive elastomers are fabricated by the polymerization of acrylic acid (AA) in polymerizable deep eutectic solvent (PDES). Liquid metal (LM) nanodroplets are used to initiate and further cross‐link polyacrylic acid (PAA) chains into a liquid‐free polymeric network without any extra initiators and cross‐linkers. The resulting liquid‐free ionic conductive elastomers exhibit high transparency (94.1%), ultra‐stretchability (2600%), and autonomous self‐healing. Spin trapping electron paramagnetic resonance and dye fading experiments reveal the generation of free radicals. UV–visible spectrometry and viscosity tests demonstrate the cross‐linking effect of Ga3+. The gelation time is much shorter than that of the conventional ammonium persulfate thermal initiation process. Furthermore, this liquid‐free polymer material is intrinsically resistant to freezing and drying, enabling it to operate under harsh conditions. In consideration of transparency, self‐healing, ultra‐stretchability, moldability, and sensory features, the resulting elastomeric conductor may hold promise for industrial applications in wearable devices, force mapping, and flexible electroluminescent devices.
Synthetic
hydrogels with hydrophobic interactions, which show excellent
mechanical performance and good anti-swelling ability in saltwater,
have great potential in various industries, such as soft robots, 3D
printing, and wearable sensors. Normally, hydrophobic molecules inside
a hydrophobic hydrogel tend to aggregate to form a large hydrophobic
domain, leading to a phase separation phenomenon because water is
a poor solvent of the hydrophobic domain. This aggregation, however,
inhibits the adhesion of the hydrophobic hydrogel to various dry materials
and thus limits its application in device and sensor industries. In
this study, we report the synthesis of hybrid hydrogels with ionically
and hydrophobically cross-linked networks. This novel hybrid hydrogel
can strongly adhere to various substrates, such as glass, polypropylene,
silicone, wood, and polytetrafluoroethylene, with a maximum adhesion
strength measured to be 100 kPa. Meanwhile, this hybrid hydrogel can
be stretched beyond 8–10 times of its initial length. We attribute
this observed strong adhesion and high toughness properties to the
synergy of electrostatic interactions and hydrophobic associations.
With the strong adhesion and excellent tensile performance, these
hydrogels may serve as a model system to explore the strong adhesion
mechanism of hydrophobic hydrogels and expand the scope of hydrogel
applications.
Hydrogel-based
electronics have received growing attention because
of their great flexibility and stretchability. However, the fabrication
of conductive hydrogels with high stretchability, excellent toughness,
outstanding sensitivity, and low-temperature stability still remains
a great challenge. In this study, a type of conductive hydrogels consisting
of a double network (DN) structure is synthesized. The dynamically
cross-linked chitosan (CS) and the flexible polyacrylamide network
doped with polyaniline constitute the DN through the hydrogen bonds
between the hydroxyl, amide, and aniline groups. This type of hydrogels
displays excellent mechanical performance, striking conductivity,
and remarkable freezing tolerance. The flexible electronic sensors
based on the double-network hydrogels demonstrate superior strain
sensitivity and linear response on various deformations. Additionally,
the good antifreezing property of the hydrogels allows the sensors
to exhibit excellent performance at −20 °C.
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