Drop impact onto semi-infinite solid surfaces with different wettabilities

The process of liquid drop impact onto a solid surface can be widely seen in both nature and industrial applications. Depending on the distance between the impact point and the surface edge (W), the impact can be categorized into three groups: (a) drop impact onto an infinite surface (surface is large, W is larger than the maximum value of radius of the lamella in all directions); (b) finite surface (surface is small, W is smaller than the maximum value of radius of the lamella in all directions); and (c) semi-infinite solid surface (W is smaller than the maximum radius of the lamella in some directions, but not all). Different from most of the literature which typically focused on the drop impact onto an infinite and/or finite solid surface, an experimental study was performed to investigate the liquid drop behavior during an impact onto a semi-infinite solid surface. In this case, part of the lamella spreads out of the surface (free lamella), while the other part of the liquid remains on the solid surface. Depending on the normalized distance ((W) over bar = W/D; D is the drop diameter), the free lamella can either recede back onto the surface ((W) over bar > 0.61) or completely break off at the surface edge ((W) over bar < 0.61). The distinctive behavior can be explained by the vertical velocity component of the free lamella and the Laplace pressure difference across the interface at the edge. The surface wettability and Weber numbers cannot determine whether the free lamella can break or recede back, but can significantly affect the breaking morphology of the free lamella. The liquid lamella on the surface behaves similarly to the drop impact on an infinite surface in the spreading phase. The value of the maximal spreading radius (r(max)) on the surface is not affected by <(W)over bar> when (W) over bar > 0.3; R-max only starts to decrease when (W) over bar is smaller than 0.3. In the receding phase, the liquid lamella on the solid surface evolves into a semicircle and a sausage shape before eventually evolving to a rounded shape.