Tutika Ravi, Kmiec Steven, Haque A B M Tahidul, Martin Steve W, Bartlett Michael D
ACS Appl Mater Interfaces. 2019 May 15;11(19):17873-17883. doi: 10.1021/acsami.9b04569. Epub 2019 May 1.
Soft composites are critical for soft and flexible materials in energy harvesting, actuators, and multifunctional devices. One emerging approach to create multifunctional composites is through the incorporation of liquid metal (LM) droplets such as eutectic gallium indium (EGaIn) in highly deformable elastomers. The microstructure of such systems is critical to their performance; however, current materials lack control of particle size at diverse volume loadings. Here, we present a fabrication approach to create liquid metal-elastomer composites with independently controllable and highly tunable droplet size (100 nm ≤ D ≤ 80 μm) and volume loading (0 ≤ ϕ ≤ 80%). This is achieved through a combination of shear mixing and sonication of concentrated LM/elastomer emulsions to control droplet size and subsequent dilution and homogenization to tune LM volume loading. These materials are characterized utilizing dielectric spectroscopy supported by analytical modeling, which shows a high relative permittivity of 60 (16× the unfilled elastomer) in a composite with ϕ = 80%, a low tan δ of 0.02, and a significant dependence on ϕ and minor dependence on droplet size. Temperature response and stability are determined using dielectric spectroscopy through temperature and frequency sweeps with DSC. These results demonstrate a wide temperature stability of the liquid metal phase (crystallizing at <-85 °C for D < 20 μm). Additionally, all composites are electrically insulating across wide frequency (0.1 Hz-10 MHz) and temperature (-70 to 100 °C) ranges even up to ϕ = 80%. We highlight the benefit of LM microstructure control by creating all-soft-matter stretchable capacitive sensors with tunable sensitivity. These sensors are further integrated into a wearable sensing glove where we identify different objects during grasping motions. This work enables programmable LM composites for soft robotics and stretchable electronics where flexibility and tunable functional response are critical.
软复合材料对于能量收集、致动器和多功能设备中的柔软且灵活的材料至关重要。一种新兴的制造多功能复合材料的方法是在高度可变形的弹性体中加入液态金属（LM）液滴，如共晶镓铟（EGaIn）。此类系统的微观结构对其性能至关重要；然而，目前的材料在不同体积负载下缺乏对粒径的控制。在此，我们提出一种制造方法，以创建具有独立可控且高度可调粒径（100 nm≤D≤80μm）和体积负载（0≤ϕ≤80%）的液态金属 - 弹性体复合材料。这是通过对浓缩的LM/弹性体乳液进行剪切混合和超声处理以控制液滴大小，随后进行稀释和均质化以调节LM体积负载来实现的。利用分析模型支持的介电谱对这些材料进行表征，结果表明，在ϕ = 80%的复合材料中，相对介电常数高达60（是未填充弹性体的16倍），损耗角正切tanδ低至0.02，且对ϕ有显著依赖性，对液滴大小依赖性较小。通过使用DSC进行温度和频率扫描的介电谱来确定温度响应和稳定性。这些结果表明液态金属相具有广泛的温度稳定性（对于D < 20μm，在<-85°C时结晶）。此外，即使在ϕ = 80%时，所有复合材料在宽频率（0.1 Hz - 10 MHz）和温度（-70至100°C）范围内均为电绝缘。我们通过创建具有可调灵敏度的全软质可拉伸电容式传感器来突出LM微观结构控制的优势。这些传感器进一步集成到可穿戴传感手套中，我们在抓握动作期间识别不同物体。这项工作为软机器人技术和可拉伸电子学实现了可编程的LM复合材料，其中灵活性和可调功能响应至关重要。
