J. Fluid Mech., 680, 477-487 (2011. 7.) [pdf]

Liquid Spreading on Superhydrophilic Microlippar Arrays

Seong Jin Kim, Myoung-Woon Moon, Kwang-Ryeol Lee, Dae-Young Lee, Young Soo Chang, Ho-Young Kim
 

When a drop is deposited on a superhydrophilic micropillar array, the upper part of the drop (referred to as the bulk) collapses while the bottom part penetrates into the 13 gaps of the array, forming a fringe film. Here we quantify the early stage dynamics of this process using a combination of experiment and theory. We show that the circular front of the fringe film spreads like t 1/2, t being time, when coupled to the bulk flow. However, the film is found to advance like t 1/3 through faceted zippering in the absence of bulk. We then show that the spreading of the bulk and the entire drop footprint follows a power law (t 1/4) that is different from Washburn’s law. This work can be a starting point to completely understand the spreading of liquids on superhydrophilic surfaces and opens questions specific to superwetting behaviour including the criteria to determine whether the fringe film will expand through lateral zipping or advance radially outwards.