Department of Electrical and Computer Engineering , University of Texas at Dallas , 800 West Campbell Road , Richardson , Texas 75080 , United States.
ACS Appl Mater Interfaces. 2019 Sep 25;11(38):35488-35495. doi: 10.1021/acsami.9b12493. Epub 2019 Sep 12.
We report gallium (Ga) coating as a simple approach to convert most common microfluidic substrates to nonwetting surfaces against surface-oxidized gallium-based liquid metal alloys. These alloys are readily oxidized in ambient air and adhere to almost all surfaces, which imposes significant challenges in mobilizing liquid metal droplets without leaving residue. Various flat substrates (e.g., PDMS, Si, SiO, SU-8, glass, and parylene-C coated PDMS) were coated with thin film (75-200 nm in thickness) of gallium by evaporation and the coated gallium formed nanoscale uneven and rough surface through Ostwald ripening with its surface covered with oxide shell. Static and dynamic contact angles of the gallium-coated surfaces were found to be greater than 160°, while dynamic contact angle measurements showed contact angle hysteresis in the range of 6.5-24.4°. Surface-oxidized gallium-based liquid metal alloy droplets were shown to bounce off and roll on the gallium-coated surfaces without leaving any residue which confirms the nonwettability of the gallium-coated flat surfaces. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed the gallium-coated flat substrates consist of nanoscale hemispherical structures with average surface roughness of 33.8 nm. Pneumatic actuation of surface-oxidized liquid metal droplets in PDMS microfluidic channels coated with gallium was conducted to confirm the feasibility of utilizing gallium coating as an effective surface modification for surface-oxidized gallium-based liquid metal droplet manipulation.
我们报告了一种简单的方法，即在大多数常见的微流控基底上涂覆镓 (Ga) 涂层，将其转化为对表面氧化的镓基液态金属合金不润湿的表面。这些合金在环境空气中很容易被氧化，并附着在几乎所有的表面上，这在不留下残留物的情况下移动液态金属液滴方面带来了重大挑战。各种平面基底（例如 PDMS、Si、SiO、SU-8、玻璃和涂有聚对二甲苯-C 的 PDMS）通过蒸发涂覆了厚度为 75-200nm 的 Ga 薄膜，并且通过奥斯特瓦尔德熟化，涂层 Ga 形成了纳米级的凹凸不平的粗糙表面，其表面覆盖有氧化壳。发现 Ga 涂层表面的静态和动态接触角大于 160°，而动态接触角测量显示接触角滞后在 6.5-24.4°范围内。表明表面氧化的镓基液态金属合金液滴在 Ga 涂层表面上反弹和滚动，而不会留下任何残留物，这证实了 Ga 涂层平面的非润湿性。扫描电子显微镜 (SEM) 和原子力显微镜 (AFM) 显示 Ga 涂层平面基底由纳米级的半球形结构组成，平均表面粗糙度为 33.8nm。通过在涂有 Ga 的 PDMS 微流控通道中气动驱动表面氧化的液态金属液滴，证实了将 Ga 涂层用作表面氧化的镓基液态金属液滴操纵的有效表面改性的可行性。
