Studying Macro- and Mesoscopic Wetting Dynamics of a Spreading Oil Droplet Using Multiple Wavelength Interferometry

In this study we present an interferometric technique based on multiple wavelengths to capture the transient free surface contour of nanoliter drops spreading on a wettable surface, in particular close to the three-phase contact line. Various data analysis procedures are evaluated in terms of error and noise sensitivity. The technique allows an unambiguous determination of the local liquid film thickness for optical path differences up to $\Delta s \approx 3.19\,\mathrm{\mu m}$ without the need of a known reference height. Film thicknesses as low as $0.1\,\mathrm{\mu m}$ can be measured with the present optical configuration. The entire three-dimensional droplet shape is investigated for different capillary numbers, allowing also reliable measurements of the time-resolved contact angle.