Simultaneous Measurement of Surface Tension and Viscosity Utilizing Droplet Merging

This paper reports on a method to simultaneous measurement of liquid surface tension and viscosity using several-μL samples. In the proposed method, a pair of small droplets aligned vertically are brought into contact to form a capillary bridge. We use a MEMS-based cantilever to measure the inner pressure of one droplet during the merging. Because as the droplets merged, the mean curvature of each droplet changes, resulting in a change in its inner pressure (Laplace pressure). The surface tension and viscosity of the liquid are calculated from the difference in the cantilever's outputs before and after the merging and the slope of the cantilever output during the beginning stage of the merging, respectively. The proposed method can be used to study the mechanism of droplet merging, which is an interesting phenomenon in the field of fluid mechanics, as well as to measure liquid mechanical properties using dilute samples.