Developing multifunctional stretchable ionic skin (I-Skin) to mimic the sensations of the human skin is of great interest and shows promising potential in wearable sensors and human−machine interfaces (HMIs). However, common ionogels prepared with small-molecule cross-linkers and single networks can hardly satisfy the requirements of adjustable mechanical properties, strong adhesion, fast self-healability, and good stability in extreme environments. Herein, an ultrastretchable (>10,000%), ultrastrong adhesive (>6.8 MPa), ultrafast selfhealable (10 s), high thermally stable (−60 to 250 °C), and three-dimensional (3D)-printable photoluminescent ionogel with shape memory properties has been designed. The ionogel consists of hyperbranched polymer covalent-cross-linked poly(zwitterionic ionic liquid)-co-poly(acrylic acid) and multiple dynamic bonding cross-linked networks. The excellent performance of the ionogel-based high-stretchable strain sensor and the triboelectric nanogenerator (TENG)-based self-powered touch sensor is further demonstrated over a wide temperature range (−40 to 150 °C). More importantly, ionogel-based I-Skin can work as an HMI for human gesture recognition and real-time wireless control of robots under extreme vacuum conditions and can also self-heal immediately along with function recovery after mechanical damage.
In this work, a stretchable, dual thermo-responsive and strain-responsive ionogel has been synthesized by one-step photopolymerization. The obtained ionogel shows an ultrahigh stretchability (∼3000%), a high ionic conductivity (up to 3.1 mS/cm), and a good temperature tolerance (−40 to 300 °C). Importantly, these ionogels show an upper critical solution temperature-type phase transition with a wide tunable phase-transition temperature (17.5−42.5 °C) and reversible color/transparency switching. In particular, the as-prepared ionogel-based flexible/wearable temperature monitors and smart windows show an excellent designability and programmability, temperature modulation ability, and thermal responsiveness. Moreover, the ionogels-based strain sensors have temperature-and straindual responsibility and a broad strain-sensing range (1−700%), which can effectively monitor various motions. This strategy of fabricating dual thermo-and strain-responsive ionogels by using a one-step method and only one polymer holds great promise for the next generation of multifunctional stimuli-responsive materials.
Here,
we report a simple method for preparing muscle-mimetic highly
tough, conductive, and stretchable liquid crystalline ionogels which
contains only one poly(ionic liquid) (PIL) in an ionic liquid via
in situ free radical photohomopolymerization by using nitrogen gas
instead of air atmosphere. Due to eliminating the inhibition caused
by dissolved oxygen, the polymerization under nitrogen gas has much
higher molecular weight, lower critical sol–gel concentration,
and stronger mechanical properties. More importantly, benefiting from
the unique loofah-like microstructures along with the strong internal
ionic interactions, entanglements of long PIL chains and liquid crystalline
domains, the ionogels show special optical anisotropic, superstretchability
(>8000%), high fracture strength (up to 16.52 MPa), high toughness
(up to 39.22 MJ/m3), and have ultrafast self-healing, ultrastrong
adhesive, and excellent shape memory properties. Due to its excellent
stretchability and good conductive-strain responsiveness, the as-prepared
ionogel can be easily applied for high-performance flexible and wearable
sensors for motion detecting. Therefore, this paper provides an effective
route and developed method to generate highly stretchable conductive
liquid crystalline ionogels/elastomers that can be used in widespread
flexible and wearable electronics.
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