Abstract
A fluid-cutting control technique was developed for generating uniform droplets of nano-liter and pico-liter grade by using gas to cut a liquid in a microchip. Numerical simulation (CFD-RC) revealed that hydrophilic or hydrophobic walls results in different cutting shape due to the reciprocation of gas and liquid. Thus, a micro-channel with innovative geometry was designed from this concept. The geometry is characteristic of an obstruction behind the cutting region. Flow rate and pressure of the liquid and gas were regulated to control the size of droplets, which is also affected by the dimensions of the micro-channel. When the distance between the wall and the obstruction reduces, the volume of liquid droplet decreases and cutting frequency becomes greater. Thus, the cutting phenomena in the two-phase flow on a super-hydrophobic wall could also be evidently improved.The present experiment utilized a gaseous stream to cut a liquid with the flow rate and pressure controlled. The microchips were manufactured by several manufactured fabrications and general comparisons for them were made. A better geometry for droplet cutting was finally concluded. Unique features of the present microchip are its production of precise nano/picoliter-grade droplets and the ease of fabrication. By combining sensors and controllers, a basis could be offered for pulsed gases to cut the liquid and separate continuous fluids, which contain two or more agents, to form droplets with specific agent. Consequently, a fluid-cutting control system was developed and it could be expected to generate uniform and/or arbitrary size droplets. Feasible applications to this technique and microchip are in biomedical technology, micro-TAS, and DNA analysis.