Pinning and depinning of Wenzel-state droplets around inclined steps

Publication date: March 2020Source: Colloid and Interface Science Communications, Volume 35Author(s): Umut Ceyhan, Aslı Tiktaş, Mert ÖzdoğanAbstractDroplets moving over inclined heterogenous substrates may pin around rough spots. A simplified model of one of these spots having a backward facing step geometry over a chemically homogeneous inclined substrate reveals that the step is responsible from the pinning-depinning of the leading edge of the droplet in Wenzel-state. We consider a two-dimensional partially wetting droplet and model its motion by the evolution equation with a precursor film model. The phase diagrams formed define pinning-depinning transition curves determined by a simple force balance of retention forces due to hysteresis, step and gravitational force. For fixed Bond number and inclination, we show that it is the slope of the step that determines transition. The existence of the multiple steps, however, alters this transition as the receding contact line may pin at the steps and leave residual droplets behind.Graphical abstract
Source: Colloids and Interface Science Communications - Category: Nanotechnology Source Type: research