Lithium molybdate disks were fabricated by moistening watersoluble Li 2 MoO 4 powder with deionized water and compressing it under a pressure of 130 MPa. Disks were postprocessed at room temperature, at 120°C, and at 540°C, which is a common sintering temperature for Li 2 MoO 4 . Regardless of the postprocessing temperature, densities as high as 87%-93% of the theoretical value were achieved. The X-ray diffraction patterns of processed disks were all the same with no signs of hydrates or constitutional water. The samples also exhibited very similar microstructures and microwave dielectric properties with a relative permittivity of 4.6-5.2 and a Q 3 f value of 10 200-18 500 at 9.6 GHz, depending on the postprocessing temperature.
Ultimately soft electronics seek affordable and high mechanical performance universal self‐healing materials that can autonomously heal in harsh environments within short times scales. As of now, such features are not found in a single material. Herein, interpenetrated elastomer network with bimodal chain length distribution showing rapid autonomous healing in universal conditions (<7200 s) with high efficiency (up to 97.6 ± 4.8%) is reported. The bimodal elastomer displays strain‐induced photoelastic effect and reinforcement which is responsible for its remarkable mechanical robustness (≈5.5 MPa stress at break and toughness ≈30 MJ m−3). The entropy‐driven elasticity allows an unprecedented shape recovery efficiency (100%) even after fracturing and 100% resiliency up to its stretching limit (≈2000% strain). The elastomers can be mechanically conditioned leading to a state where they recover their shape extremely quickly after removal of stress (nearly order of magnitude faster than pristine elastomers). As a proof of concept, universal self‐healing mechanochromic strain sensor is developed capable of operating in various environmental conditions and of changing its photonic band gap under mechanical stress.
Self‐Healing Elastomers
Soft electronics seek all‐around high mechanical performance universal self‐healing elastomers. In article number 2103235, Jarkko Tolvanen and co‐workers report design strategy to achieve tough and resilient universal self‐healing elastomer. The resilin‐inspired bimodal siloxane‐based elastomer benefits from combination of soft and hard phases. The cover displays existing phase‐separated morphology during shape recovery captured by optical microscopy.
A family of low-temperature cofired ceramics (LTCC) based on mixtures of a commercial dielectric, MgTiO 3 -CaTiO 3 (designated MMT-20) and ZnO, SiO 2 , and B 2 O 3 , has been investigated for microwave applications. The main objective was to optimize the three key properties-relative permittivity ( r ), dissipation factor (DF), and the temperature dependence of the microwave resonance frequency ( f )-through adjustment of the composition. A further objective was to estimate the limits on compositional variability while maintaining acceptable properties. The developed microstructures, after firing at 900°C, were studied using X-ray diffractometry and scanning electron microscopy/energy dispersive spectrometry techniques and compared with the dielectric parameters. The optimum composition (wt%) was found to lie in the ranges 45.8 -44.9, ZnO; 17.25-17.55, B 2 O 3 ; 6.95-7.05, SiO 2 ; and 30 -30.5, MMT-20, yielding values of r ؍ 8.5-9.5, DF < 0.93 ؋ 10 ؊3 ppm/K, and f < ؎10 ppm/K.
Next-generation, truly soft, and stretchable electronic circuits with material level self-healing functionality require high-performance solution-processable organic conductors capable of autonomously self-healing without external intervention. A persistent challenge is to achieve required performance level as electrical, mechanical, and self-healing properties optimized in tandem are difficult to attain. Here heterogenous multiphase conductor with cocontinuous morphology and macroscale phase separation for ultrafast universally autonomous self-healing with full recovery of pristine tensile and electrical properties in less than 120 and 900 s, respectively, is reported. The multiphase conductor is insensitive to flaws under stretching and achieves a synergistic combination of conductivity up to ≈1.5 S cm −1 , stress at break ≈4 MPa, toughness up to >81 MJ m −3 , and elastic recovery exceeding 2000% strain. Such properties are difficult to achieve simultaneously with any other type of material so far. The solution-processable multiphase conductor offers a paradigm shift for damage tolerant and environmentally resistant soft electronic components and circuits with material level self-healing.
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