Sun Xuyang, Guo Rui, Yuan Bo, Chen Sen, Wang Hongzhang, Dou Mengjia, Liu Jing, He Zhi-Zhu
Beijing Key Laboratory of Cryo-Biomedical Engineering and CAS Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China.
Department of Biomedical Engineering, School of Medicine, Tsinghua University Beijing 100084, P. R. China.
ACS Appl Mater Interfaces. 2020 Aug 26;12(34):38386-38396. doi: 10.1021/acsami.0c10409. Epub 2020 Aug 12.
Shape transformable materials that can respond to external environments have attracted widespread interest over the fields of soft robotics, flexible electronics, and tissue engineering. Among stimuli-responsive materials, liquid metals exhibit rather unique characteristics of versatile morphological changes upon diverse stimuli, including chemicals, electrical field, and mechanical force, etc. Herein, a superfast (few milliseconds), large-scaled (13.8% deformation increase), and fierce (cracks formation) transformation of liquid metal microdroplets (LMMs) with strong impulse expanded force due to liquid-solid phase transition in a dual fluid system composed of LMMs and aqueous solution is reported. When subject to low-temperature stimulus, LMM would transform from ellipsoidal shape to amorphous shape induced by thermal stress, driving the shape morphing. Furthermore, the phase changes of LMMs as well as the formation of surrounding ice crystals are proven to be responsible for this phenomenal behavior. The densification of ice crystals is demonstrated to play a significant role in the transformable behavior. In particular, these nonconductive LMMs in aqueous solutions are discovered to turn into conducive materials with an impedance change of about 10 times. The present discovery is of fundamental and practical significance, and would open new venues in fields such as fluid mechanics, thermal science, flexible electronics, biomedicine, and so forth.
能够响应外部环境的形状可变形材料在软机器人技术、柔性电子学和组织工程等领域引起了广泛关注。在刺激响应材料中，液态金属在包括化学物质、电场和机械力等多种刺激下表现出相当独特的多种形态变化特征。在此，报道了在由液态金属微滴（LMM）和水溶液组成的双流体系统中，由于液-固相变，液态金属微滴发生超快（几毫秒）、大规模（变形增加13.8%）和剧烈（形成裂纹）的转变，具有强大的脉冲膨胀力。当受到低温刺激时，LMM会因热应力从椭圆形转变为无定形，驱动形状变形。此外，LMM的相变以及周围冰晶的形成被证明是这种现象行为的原因。冰晶的致密化在可变形行为中起着重要作用。特别地，发现这些在水溶液中的非导电LMM会变成阻抗变化约10倍的导电材料。本发现具有基础和实际意义，并将在流体力学、热科学、柔性电子学、生物医学等领域开辟新的途径。
