研究背景
随着人们对电子设备的要求越来越高，可穿戴技术已经发展成为最具成长性的产业之一。与传统电子设备不同，可穿戴设备具有理想的柔性和便利性，易于与人体结合。近年来随着对导电聚合物和柔性传感器研究的不断深入，多功能可穿戴电子设备在传感、驱动、电子皮肤、人体健康检测、人机交互等方面展现出广阔的发展前景。具有良好柔韧性的传感器是智能电子设备的关键感知单元,以往的研究大多集中在对外界刺激的高灵敏度和快速响应上。然而，由于结构设计的困难，对电子设备实际应用非常重要的高能量冲击下的稳定性和灵敏度往往被忽视。因此，人们迫切希望可穿戴设备能够应对日常生活中无处不在的机械碰撞和极端情况下的高速冲击，同时还能感知冲击力。因此，开发一种简便、低成本、高效率的策略来制造集高柔性、良好导电性和优异抗冲击性于一体的多功能可穿戴电子器件是非常必要的。
作为一种古老的天然材料，皮革具有三维多孔结构，由多层胶原纤维束组成，可作为柔性电子器件的多功能基体。然而，尽管皮革自古以来就被用作天然的保护装置，但其保护性能的进一步提高仍然很少。此外，已有研究证明，柔性基底的微观结构可以显著改善柔性传感器的传感性能。在优异的柔韧性和耐磨性方面，皮革与多功能的整合在开发具有优异保护性能的高性能可穿戴电子皮革中起着关键作用。
研究成果
本研究采用“软-韧“耦合设计方法，将剪切加硬凝胶(SSG)、天然皮革和无纺布(NWF)有机结合，制备出具有高抗冲击保护、压阻传感、电磁干扰屏蔽和人体热管理性能的皮革/MXene/SSG/NWF(LMSN)复合材料。由于皮革的多孔纤维结构，MXene 纳米片能够穿透皮革构建稳定的三维导电网络，因此LM和LMSN复合材料均表现出优异的导电性、高焦耳加热温度和高效的电磁干扰屏蔽效果。由于SSG具有优异的能量吸收能力LMSN复合材料具有巨大的力缓冲能力(约65.5%)、优异的能量耗散能力(50%以上)以及高达91 m s-1的极限穿透速度，显示出非凡的抗冲击性能。LMSN 复合材料具有与压阻传感(电阻减小)和冲击刺激(电阻增大)相反的非常规传感行为，因此可以区分低能量和高能量刺激。最终，进一步制备出具有热管理和冲击监测性能的软防护背心，并显示出典型的无线冲击传感性能。该方法有望在下一代可穿戴人体防护电子设备中得到广泛应用。相关研究以“Wearable Safeguarding Leather Composite with Excellent Sensing, Thermal Management, and Electromagnetic Interference Shielding”为题发表在Advanced Science期刊上。
图文导读
Figure 1. a) The fabrication process of the MXene nanosheets. b) The schematic diagrams show the preparation of the LMSN composite. c) LMSN composite with superb properties.
Figure 2. a) The digital and b) SEM images of the grain side of the leather. c) The digital and d) SEM images of the fiber side of the leather. e) The AFM image of the MXene nanosheet. f) The microscopic CT images of leather and LM. g) The digital and h) SEM images of the LM surface. i) The SEM and j) corresponding elemental mapping images of the LM surface. k) The cross-sectional SEM and l) corresponding elemental mapping images of the LM. m) The XRD patterns of Ti3AlC2 precursor, Ti3AlC2, and LM. n) The electrical conductivity of LM composites with different MXene contents. o) The tensile mechanical property and p) the tensile modulus of LM composites.
Figure 3. a) The schematic and b) optical images of LMSN. c) The cross-sectional optical image of the LMSN. d) The cross-sectional SEM image of the LM. e) The SEM image of SSG. f) The Fourier-transform infrared (FT-IR) spectrum analyses of SSG. g) The rheological properties of SSG. h) The conductivity of LMSN composites with different MXene contents. i) The percolation threshold of LMSN composites.
Figure 4. The EMI shielding effectiveness of a) LM and b) LMSN composites with different MXene contents. c) The contribution of reflection (SER) and absorption (SEA) of LMSN composites. d) The percentage of SEA to SET of LMSN composites. e) The R, T, and A coefficients of LMSN composites. f)The EMI shielding effectiveness of LMSN10 before and after impact. g) The schematic illustration of the EMI shielding mechanism.
Figure 5. a) The relative resistance changes of LMSN composites upon various pressures. b) The schematic illustration of the piezoresistive sensing mechanism. c–e) The relative resistance changes of LMSN10 composite under the triangular and square waves with different frequencies. f) The force and displacement curve of the square wave at 0.025 Hz. g) The response time of the LMSN10 composite. h) The resistance changes of the LMSN sensor under 1000 cycles of loading/unloading.
Figure 6. a) The schematic diagram of the drop hammer testing system. b) The peak forces of leather and LM composites at 40 cm. c) The force–time curves of diverse samples at 20 cm. d) The peak forces of diverse samples at the heights of 10–60 cm. e) The anti-impact mechanism schematic diagram of SSG. f) The acceleration–time curves and g) energy dissipation of the LMSN composite at the heights of 10–60 cm. h) The force–time curves, i)acceleration–time curves, and j) energy dissipation of the LMSN composite with the different mass of SSG at 40 cm. k) The resistance changes of the LMSN composite under different impacts.
Figure 7. a) The diagram of the ballistic impact testing system. b,c) The high-speed camera images of the impact process of leather and LMSN composite. d) The schematic diagram of the wireless sensing monitoring system. e) The residual velocity–incident velocity relationships of leather and LMSN composite. f) The energy dissipation results under different incident energy. g) The resistance changes of the LMSN composite at the penetrated and not penetrated states. h) The wireless alarm schematic diagram when the sample was penetrated.
Figure 8. a) Schematic of LMSN-based Joule heating effect (partial illustrations are sourced from the freepik website). b) The temperature–time curves of LM composites with different MXene contents at 3.0 V. c) The temperature–time curves of LMSN10 at different voltages. d) The temperature–time curves of LM10 under 50 heating/cooling cycles. e) Long-term Joule heating performance of LM10 at 3.0 V. f) The step precision heating performance of LM10 at 1.0–3.0 V. g) The corresponding voltage and power changes curves of (f). h) The IR camera images of the Joule heating process at 3.0 V.
Figure 9. a) Practical applications of the LMSN composite (partial illustrations are sourced from the freepik website). b) The design diagram of the personal safety protection vest. c,d) The optical image and IR camera images of the vest on a mold. The resistance changes caused by knocking are monitored by e) a wireless transmission system and f) the impedance meter test system.
总结与展望
综上所述，本研究报道了一种由 LM、剪切增硬凝胶和 NWF 组装而成的 LMSN 复合材料通过吸滤将 MXene纳米片浸入皮革的多孔纤维网络结构中，形成高效的三维导电网络，赋予LM优异的导电性能。因此，LM 复合材料具有优异的电磁干扰屏蔽、压阻传感和焦耳加热性能。在MXene含量较低的情况下，由于多级光纤结构中的欧姆损耗和电磁波的多次反射，LM10复合材料实现了约26 dB的EMI SET，在3.0 V 下具有约98℃的高饱和温度，并且由于电阻的稳定性，通过电压实现了精确的温度控制。此外，LMSN 复合材料在3.0 V电压下的饱和温度也高达约87℃，并且在组装SSG和NWF后具有相同的EMI 屏蔽能力。有趣的是，与LM 复合材料相比，LMSN 复合材料具有更好的抗冲击性能。由于SSG 的速率依赖特性和耗能性能，LMSN 复合材料具有明显的力缓冲性能(约65.5%)和耗能性能(50%以上)，极限穿透速度高达 91 m s-1，优于纯皮革。此外，LMSN 复合材料可通过输出负向和正向电阻变化来区分低能量和高能量刺激。最终设计出一种新型智能防护背心，该背心具有优异的热管理和无线冲击传感性能，证明了 LMSN 复合料在下一代可穿戴电子设备人体防护方面的应用潜力。
文献链接
Wearable Safeguarding Leather Composite with Excellent Sensing, Thermal Management, and Electromagnetic Interference Shielding
https://doi.org/10.1002/advs.202302412
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