Xu Xiao-Yu, Xu Zheng, Wang Xiao-Dong, Qin Shao-Chun, Qian Yan-Wen, Wang Li-Ding, Liu Jun-Shan
Key Laboratory for Micro/Nano Technology and System of Liaoning Province, Dalian University of Technology, Dalian 116024, China.
Langmuir. 2021 Feb 23;37(7):2334-2340. doi: 10.1021/acs.langmuir.0c03154. Epub 2021 Feb 2.
In transfer printing, the loaded droplet on the probe has a significant influence on the dispensing resolution. A suitable loading approach for a high-viscous liquid is highly required. Herein, a novel electrostatic loading method is presented, in which the main aim is to control precisely the formation and breaking of a cone-shaped liquid bridge. An experimental device is developed. The influence of electrical and geometric parameters on the feature size of the liquid bridge is investigated in detail. In the formation of the liquid bridge, the increase of voltage or the decrease of the air gap can enhance the electric field intensity, thus reducing the formation period and increasing the initial cone tip diameter of the liquid cone. After the liquid bridge is formed, both the circuit current implying the liquid wetted area on the probe surface and the lifting velocity of the probe are utilized to further regulate the volume of the loaded droplet. Loaded droplets ranging from 60 to 600 pL are obtained via the method with a standard deviation of 4 to 30 pL. Moreover, a dot array is transferred with different loaded droplets. The minimum diameter of the printed dots is about 140 μm with a variation less than 5%. The advantages include the reduced risk of contamination, the droplet-size independent of the size of the probe, and the low cost of the device.
在转印过程中，探针上加载的液滴对分配分辨率有显著影响。因此，对于高粘性液体，迫切需要一种合适的加载方法。在此，提出了一种新型的静电加载方法，其主要目的是精确控制锥形液桥的形成和破裂。开发了一种实验装置。详细研究了电学和几何参数对液桥特征尺寸的影响。在液桥形成过程中，电压的增加或气隙的减小会增强电场强度，从而缩短形成周期并增大液锥的初始锥尖直径。液桥形成后，利用暗示探针表面液体润湿面积的电路电流和探针的提升速度来进一步调节加载液滴的体积。通过该方法获得的加载液滴体积范围为60至600皮升，标准偏差为4至30皮升。此外，用不同加载体积的液滴转印点阵。打印点的最小直径约为140微米，变化小于5%。其优点包括降低污染风险、液滴尺寸与探针尺寸无关以及装置成本低。
