鞘状碳纳米管人工肌肉纤维在弱电流刺激下的驱动性能提升机制

Enhancement actuation mechanism for the sheath-run artificial muscle fiber under weak current

电热驱动的鞘状人工肌肉已经展示出广阔的应用前景.当受到高电流产生的焦耳热影响时,它们的鞘层会膨胀和软化,有效地释放芯部纤维内储存的扭转能量,这种现象显著地提高了驱动性能.本工作制备了一种包裹在聚二甲基硅氧烷(PDMS)鞘层中的预捻碳纳米管(CNT)人工肌肉纤维.施加频率为0.25 Hz的50 mA电流,其可以产生13.28%的收缩变形和9.82 MPa的收缩应力,功率密度为3.8 W g^(−1).得益于非螺旋结构,CNT纤维@PDMS的运行速率可达42%s^(−1),我们据此开发了快速运行的开关和仿生臂.有趣的是,我们观察到即使在较弱的电流不足以诱导驱动所需的PDMS鞘层膨胀和软化的情况下,CNT纤维@PDMS的驱动性能也有所改善.为了解释这一现象,我们提出了一种鞘层致密化机制.当电流通入CNT纤维时,其内部CNTs间产生的安培吸引力也会引发驱动,PDMS鞘层在固化过程中产生沿CNT纤维径向分布的收缩应力,会使CNTs间距减小,从而提升安培吸引力.我们通过检测CNT纤维@PDMS在不同温度下的驱动行为、内部微观结构、力学和电学性能的变化证实了这种致密化机制的存在,并分析了整个驱动过程中能量的变化.

Electrothermal sheath-run artificial muscles hold great promise for various applications.Their sheath expands and softens when subjected to Joule heat generated by high currents,effectively releasing the stored torsional energy within the core fiber.This phenomenon significantly enhances actuation performance.In this study,an artificial muscle composed of pre-twisted carbon nanotube(CNT)fiber encased in polydimethylsiloxane(PDMS)sheath was prepared.Under a 50-mA current at a frequency of 0.25 Hz,it demonstrated a 13.28%contraction stroke and 9.82 MPa contraction stress,with a power density of 3.8 W g^(−1).Notably,thanks to its non-coiled structure,CNT fiber@PDMS can operate at speeds of up to 42%s−1,and be applied to switches and biomimetic arms.Interestingly,we observed improved actuation performance even with relatively weak currents that were insufficient to induce the expansion and softening of the PDMS sheath typically required for actuation.To explain this phenomenon,a mechanism involving the densification of the CNT fiber by the PDMS sheath was proposed.When electrified,the CNT fiber initiates Ampere attraction forces among its internal CNTs,generating actuation.Simultaneously,the curing process of the PDMS sheath induces radial compressive stresses,reducing the spacing between CNTs and thereby increasing the Ampere attraction force.We substantiated this mechanism through investigations into actuation behavior at different temperatures,internal microstructure,and the mechanical and electrical properties of the CNT fiber@PDMS,ultimately providing a comprehensive analysis of energy changes throughout the actuation process.