Study on Liquid-Bridging Induced Microscale Contact of Two Liquid Droplets

The field of microfluidics is developing with advances in MEMS, biotechnology and μ-TAS technologies. In various devices, interfacial energy is a dominant factor for liquid movement in a microchannel. The surface tension and interfacial tension values are necessary to analyze the liquid behavior in the microchannel. Evaluating the values of interfacial tension is especially important for multiphase flow. A pendant drop method is usually used to measure the interfacial tension, however, this method has some inconveniences. For example, the pendant drop method demands strict accuracy for measuring the droplet size when the droplet has a non-spherical shape. Moreover, it needs an accurate value of the density difference between the two liquids. In this work, a new measurement method named “Liquid-bridging Induced Micro Contact Method” has been developed to overcome the weaknesses of the existing methods. In a previous study, we obtained the interfacial tension from bridging of two liquid droplets on the tip of opposing round metal rods. In this study, we have examined the liquid-bridging of two extruded liquid droplets out of a micro glass tube. By measuring the radii of curvature of each liquid surface and interface, we calculate the Laplace pressure on the surface and interface, and derive the interfacial tension value using the Laplace equation. To prove these two methods are reliable, we have compared the results obtained in this experiment to that of the pendant drop method. As a liquid droplet comes into contact with an opposite liquid droplet the phenomenon is recorded using a CCD camera and high speed camera. The results show that the values of interfacial tension obtained from two methods are approximately the same. Therefore, the liquid-bridging induced micro contact method has been shown to be capable of interfacial tension measurements.