2014 Volume 9 Issue 1 Pages JFST0010
The author has studied the wettability of micro-structured surfaces, some of which have exhibited drag reduction in the channel flow of water in previous experiments. All of the five different patterned surfaces tested here comprise microscale cylindrical pillars of constant length, thickness, and interval. The movement of the wetting front across the microstructured surface has been observed in order to assess the wettability. The surface with dense and long pillars exhibited the slowest movement of the wetting front; meaning that it has the best ability to maintain an air layer, which is the cause of drag reduction in channel flow. Those surfaces having the same number of pillars as the least wettable surface, but with two different pillar lengths, were next in terms of wettability. The experimental results agreed with analysis using a Washburn-type equation, which showed that the ratio between the actual surface area and the apparent area is an important parameter in estimating the wettability of patterned surfaces.