Visualization of contact line motion on hydrophobic textures

Contact angle hysteresis (CAH) has important implications in a variety of natural and industrial applications. The contact line motion of Cassie drops on microtextured surfaces is directly visualized using high-magnification imaging and fluorescence microscopy. The advancing contact line is observed to glide smoothly over the micro-posts, whereas the receding contact line exhibits significant stick-slip. Using simultaneous measurements of drop width and contact angle, the authors quantify stick-slip amplitude and define contact width hysteresis. A new scaling is proposed for drop roll-off angle a wherein sina is linearly proportional to the practical work of adhesion (1 + cos theta(r)). This study provides insight into the dynamic nature of CAH and the design of superhydrophobic surfaces with optimal drop shedding.