Isothermal Evaporation of a Thin Liquid Droplet on Porous Surfaces: Measurements of Thicknesses by the Schlieren Method

Abstract

This study examines the evaporation of sessile droplets at the final stage, when the contact angle is less than 20\({}^{\circ|}\) and the droplet has become thin. The investigation is conducted on low-reflective porous surfaces, namely robust black silicon with a TiO\({}_{2}\) coating and a glass plate coated with graphite. The high-speed Schlieren technique with a graded filter was employed to measure thicknesses down to 2 \(\mu\)m. The characteristics of non-volatile water and volatile ethanol thin liquid films were visualized. It was observed that the structure of surfaces and the type of liquid play a crucial role in the dynamics and rupture of thin liquid films.