Jacob Alan R, Parekh Dishit P, Dickey Michael D, Hsiao Lilian C
Department of Chemical and Biomolecular Engineering , North Carolina State University , 911 Partners Way , Raleigh 27695 , United States.
Langmuir. 2019 Sep 10;35(36):11774-11783. doi: 10.1021/acs.langmuir.9b01821. Epub 2019 Aug 27.
Gallium and its alloys react with oxygen to form a native oxide that encapsulates the liquid metal with a solid "skin". The viscoelasticity of this skin is leveraged in applications such as soft electronics, 3D printing, and components for microfluidic devices. In these applications, rheological characterization of the oxide skin is paramount for understanding and controlling liquid metals. Here, we provide a direct comparison of the viscoelastic properties for gallium-based liquid metals and illustrate the effect of different subphases and addition of a dopant on the elastic nature of the oxide skin. The du Noüy ring method is used to investigate the interfacial rheology of oxide skins formed by gallium-based liquid metal alloys. The results show that the oxide layer on gallium, eutectic gallium-indium, and Galinstan are viscoelastic with a yield stress. Furthermore, the storage modulus of the oxide layer is affected by exposure to water or when small amounts of aluminum dopant are added to the liquid metals. The former scenario decreases the interfacial storage modulus of the gallium by 35-85% while the latter increases the interfacial storage modulus by 25-45%. The presence of water also changes the chemical composition of the oxide skin. Scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy suggest that a microstructural evolution of the interface occurs when aluminum preferentially migrates from the bulk to the surface. These studies provide guidance on selecting liquid metals as well as simple methods to optimize their rheological behavior for future applications.
镓及其合金与氧气反应形成一种天然氧化物，该氧化物用一层固体“外皮”包裹住液态金属。这种外皮的粘弹性被应用于软电子学、3D打印以及微流控设备部件等领域。在这些应用中，氧化物外皮的流变学特性对于理解和控制液态金属至关重要。在此，我们对镓基液态金属的粘弹性特性进行了直接比较，并阐述了不同亚相以及添加掺杂剂对氧化物外皮弹性性质的影响。采用杜诺伊环法研究了镓基液态金属合金形成的氧化物外皮的界面流变学。结果表明，镓、共晶镓铟和镓锡合金上的氧化层具有粘弹性且存在屈服应力。此外，氧化层的储能模量会受到暴露于水或向液态金属中添加少量铝掺杂剂的影响。前一种情况会使镓的界面储能模量降低35% - 85%，而后一种情况会使界面储能模量提高25% - 45%。水的存在也会改变氧化物外皮的化学成分。扫描电子显微镜、能量色散X射线光谱（EDS）和X射线光电子能谱表明，当铝优先从本体迁移到表面时，界面会发生微观结构演变。这些研究为选择液态金属以及优化其流变行为以用于未来应用提供了简单方法和指导。
