Abstract
In a case of complete wetting, a very thin film spreads ahead of the macroscopic edge of the droplet on a solid surface. This thin film is called precursor film. The precursor film plays a key role in many practical processes, such as micro heat pipe, thin-film coating and oil recovery. The authors carry out experimental works focusing on the spatio-temporal growth of the precursor film at an early stage of the droplet spreading on the substrate. Simultaneous observations of the macroscopic and microscopic edge of the droplet by Brewster angle microscope enable ones to detect the precursor film at a growing stage. For the film thickness, the authors employ a confocal laser displacement sensor to measure temporal variation in thickness of the precursor film at a designated point.
