Air-water meniscus shape in superhydrophobic triangular microgroove is dictated by a critical pressure under dynamic conditions

We bring out a critical force for shape transition of air-water meniscus in superhydrophobic triangular microgrooves under dynamic conditions, considering an intricate interplay of the viscous and capillary forces. A closed form theoretical expression for the critical force depicts its explicit dependence on the groove geometry and relevant physical properties. A negative value of this critical force denotes a convex meniscus shape, whereas a positive value signifies a concave meniscus shape. Considering the shape transition, the critical pressure is further interpreted to denote a physical condition under which the meniscus is nontrivially flat, despite the existence of surface tension forces. Our analysis opens up a paradigm by which the meniscus shape in a groove can be virtually controlled at will, consistent with the specific requirements such as drag reduction, as demanded by the application on hand.