Precursor Film Formation Process Ahead Macroscopic Contact Line of Spreading Droplet on Smooth Substrate

The authors pay their special attention to formation process of wafer-thin liquid film, known as ‘precursor film,’ ahead moving macroscopic contact line of a droplet spreading on a solid substrate. The spreading droplet on the solid substrate is accompanied with the movement of a visible boundary line so-called ‘macroscopic contact line.’ Existing studies have indicated there exits a thin liquid film known as ‘precursor film’ ahead the macroscopic contact line of the droplet. The present author’s group has dedicated their special effort to detect the formation process of the precursor film by applying a convectional laser interferometry and a high-speed camera, and to evaluate the spreading rate of the precursor film. In the present study, existing length of the precursor film at a very early stage of the droplet spreading is evaluated by applying a Brewster-angle microscopy as well as the interferometer. The authors extend their attention to the advancing process of the precursor film on inclined substrate.