Time-resolved, three-dimensional quantitative microscopy of a droplet spreading on solid substrates

A polarized microscope was used to study the spreading of mercury droplets on thin silver films. Using the differential interference contrast (DIC) method and semi-quantitative measurements of the optical path difference (OPD), the three-dimensional shape of the liquid droplet that wets the solid surface was constructed with an angle resolution of 1 degrees. The evolution of the droplet shape was determined with a time resolution of 0.04 s. The quantitative results are compared with other wetting-reaction systems. In particular, it is demonstrated that the droplet has a spherical-cup shape during the entire wetting-reaction process.