Fabrication and drag reduction of controllable wetting surfaces

On the one hand, 3 types of dopamine based copolymers were synthesized which can vary the surface wettability of smooth surface, on the other hand, superhydrophobic surface was fabricated by coating low surface energy material on rough surface. The drag reduction properties of samples with different wettability were measured in laminar flow and turbulent flow by rheometer and water tunnel equipments, respectively. It was found that drag reduction of samples increased from 1.8% to 7.2%, 7.9% and 14.9% with an increase of contact angles from 13° to 45°, 113° and 161° in the laminar flow, and the mean values of drag reduction of the first three samples increased from 0.8% to 1.9% and 6.8% (corresponding maximum values were 3.6%, 9.0% and 18%, respectively) in turbulent flow. It was concluded that the increase of water contact angle of material surface resulted in an increase of drag reduction in both laminar and turbulent flow.