Impact of geometric factors of roughness on the dewetting dynamics of a liquid film in the Wenzel state

An axisymmetric two-phase lattice Boltzmann method is adopted to simulate the dewetting dynamics of the liquid film on a substrate fabricated with different types of roughness: pillar-type, nail-type and mushroom-type. The liquid film remains in the Wenzel or half-Wenzel state. The dewetting of the liquid film occurs after generating an initial dry spot on the substrate and forming a contact line between the liquid film, gases and the substrate. The dewetting is characterized by the continuous size growth of the contact line's radius. The effect of the geometric factors of the roughnesses on the dewetting dynamics is analyzed in detail. For the pillar-type roughness, three dewetting modes, named 'no residual,' 'part residual' and 'full residual', are identified, and a mode map that depends on the geometrical factors is given. For the nail-type roughness, the dewetting process is found to be clearly restrained. For the mushroom-type roughness, only the 'full residual' mode is found, and the depth of the grooves hardly affects the dewetting speed, if the liquid film remains in the Wenzel state; but if it remains in the half-Wenzel state, the liquids would be brought out completely from the grooves and thus result in a faster dewetting speed under smaller penetration of the liquid film. The results indicate that the different geometric elements of the roughness could affect the dewetting speed to different degrees. Determining how the structured roughness affects the dewetting speed can help the industry control the dewetting process of the liquid film. (paper)