Abstract
We conduct an experimental study focusing on the spreading droplet in the vicinity of the boundary line of solid-liquid-gas interface, which is called macroscopic contact line (M-CL). When the droplet spreads on the solid surface completely, a very thin film whose thickness is of a few nm is formed ahead of the M-CL. This thin film is so-called precursor film. We pay our attention to the spatio-temporal growth of the precursor film in terms of its thickness and length at an early stage of the droplet spreading. The target system is a tiny droplet of 2-cSt and 5-cSt silicone oil spreading on the glass substrate. We apply confocal laser displacement sensor to measure the temporal variation of the precursor film thickness at a designated point, and the Brewster angle microscope to detect the precursor film ahead of the M-CL and to evaluate its existing length. We show the effects of the liquid viscosity on the development of precursor film through the results of both its length and thickness.
