Qingqing Yang,Chaosheng Yuan,Yongfu Liang,Xiang Zhu,Zheng Wang,Kai Shi,Xuerui Cheng,Lei Su
The phase transition of pyrrole was studied under static pressure and dynamic pressure by in situ Raman spectroscopy. Under static compression, pyrrole underwent three phase transitions: a liquid-to-crystal (phase Ⅰ) transition at 1.15 GPa, followed by transformation into phase II at 7.45 GPa and the start of amorphous phase transition at 16 GPa. Under dynamic compression, pyrrole was compressed into an amorphous phase as the pressure increased from 0.71 GPa to 5.02 GPa, 8.07 GPa, 10.30 GPa, 11.30 GPa and 12.84 GPa within 5 ms, respectively. Rapid compression rate and high pressure provide a greater degree of disorder in amorphous pyrrole by fitting the partial Raman peak linewidth with pressure. During the pressure relief process, the amorphous pyrrole crystallized and transformed into phase II at 3.20 GPa and then reverted to its initial liquid state at around 0.55 GPa. The phase behaviors can be attributed to different solidification mechanisms of liquid pyrrole induced by different compression rates under the two compression conditions.
Ping Hu,Yuan Cheng,Peng Wang,Xiang Guo,Chen Ma,Qiang Qu,Xinghong Zhang,Shanyi Du
Inspired by natural exoskeleton composites in arthropods consisting of regularly oriented fibrous chitin within continuous matrices, a novel rolling compacted method was developed to enable controlled orientation of carbon fibers in UHTCs. Using rolling compaction, carbon fibers were arranged in ZrC-SiC matrix along highly consistent direction, in which ceramic powders were uniformly introduced into intrafascicular and interfascicular spaces of fiber bundles. The fabricated C f /ZrC-SiC composite revealed an extendedly graceful fracture pattern and stably impeded crack propagation with a flexural strength and fracture toughness at 227 ± 3 MPa and 5.46 ± 0.14 MPa m 1/2 . An exceptional work of fracture of 3244 ± 76 J/m 2 was achieved, one order of magnitude higher than those of UHTCs, attributed to toughening mechanism of oriented carbon fibers such as fiber pull-out and bridging accompanied by crack deflection and termination. This work provides an easily feasible way to tailor mechanical performance for fiber-reinforced composites through site-specific optimization of fiber orientation .
Flexible high-performance piezoelectric nanogenerator (PENG) excel in converting mechanical energy into electrical energy and exhibit remarkable sensitivity, a feature that is paramount for the development of self-driven piezoelectric sensors . In this study, electrospinning technology was used to prepare poly (vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] based piezoelectric nanofiber composite films containing potassium-sodium niobate nano particles (KNN NPs) and Nb 2 CT x co-doping, as well as single-component doping. The co-doped composite film attained an optimal β-phase content of 91.33%. Owing to the enhanced dipole alignment and interface charge polarization, the piezoelectric performance of the co-doped composite film was significantly enhanced compared to that of single-component doping. The co-doped piezoelectric composite film displayed a stable maximum output voltage of 20 V and an output current of 1.46 μA. The peak instantaneous power output was measured at 9.9 μW under the optimal resistive load of 10 MΩ. Durability testing over 2000 cycles affirmed the excellent mechanical stability of the piezoelectric composite film. Moreover, the fabricated piezoelectric composite film showed considerable potential in applications such as monitoring human activities and serving as an early warning system for natural disasters such as landslides, as indicated by the test results.
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