Scalable superhydrophobic coating with controllable wettability and investigations of its drag reduction

Superhydrophobic surface (SHS) has always been considered to be favorable for reducing drag force due to the air layer in surface asperities, however, debates over whether such surface could reduce the drag force still remains. In this study, steel surface was sprayed with suspension that contained PMMA and hydrophobic nanoscale silica, and the obtained surface showed variable contact angle from 94 degrees to 159 degrees , sliding angle from 90 degrees to 2 degrees, suggesting the controllable wettability; besides, the facile preparation process showed promising prospect to be scaled up. We studied the drag-reducing property of treated steel via sailing test and rotary disc test, results showed that SHS could efficiently reduce the drag force under low fluidic condition; surprisingly, for the intense turbulent flow, the SHS exhibited a drag-increasing effect, indicating that such surface only functions under mild flow condition.