Science and Technology on Microsystem Laboratory, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, 200050, China.
School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing, 100049, China.
Sci Rep. 2017 Aug 8;7(1):7552. doi: 10.1038/s41598-017-07867-5.
The directional and long-range droplet transportation is of great importance in microfluidic systems. However, it usually requires external energy input. Here we designed a wettability gradient surface that can drive droplet motion by structural topography. The surface has a wettability gradient range of over 150° from superhydrophobic to hydrophilic, which was achieved by etching silicon nanopillars and adjusting the area of hydrophilic silicon dioxide plane. We conducted force analysis to further reveal the mechanism for droplet self-propulsion, and found that the nanostructures are critical to providing a large driving force and small resistance force. Theoretical calculation has been used to analyze the maximal self-propulsion displacement on different gradient surfaces with different volumes of droplets. On this basis, we designed several surfaces with arbitrary paths, which achieved directional and long-range transportation of droplet. These results clarify a driving mechanism for droplet self-propulsion on wettability gradient surfaces, and open up new opportunities for long-range and directional droplet transportation in microfluidic system.
在微流控系统中，定向和长程液滴输运具有重要意义。然而，这通常需要外部能量输入。在这里，我们设计了一种润湿性梯度表面，通过结构形貌可以驱动液滴运动。该表面的润湿性梯度范围超过 150°，从超疏水到亲水，这是通过蚀刻硅纳米柱并调整亲水性二氧化硅平面的面积来实现的。我们进行了力分析，以进一步揭示液滴自推进的机制，发现纳米结构对于提供大驱动力和小阻力至关重要。理论计算用于分析不同体积液滴在不同梯度表面上的最大自推进位移。在此基础上，我们设计了具有任意路径的几个表面，实现了液滴的定向和长程输送。这些结果阐明了润湿性梯度表面上液滴自推进的驱动机制，为微流控系统中长程和定向液滴输送开辟了新的机会。
