Forced Wetting and Dewetting of Water and Oil Droplets on Planar Microfluidic Grids.

We experimentally study the wetting behavior of small water and oil droplets spreading and receding from textured surfaces made using a backside laser processing technique. A dual image acquisition system enables the three-dimensional characterization of both wetted area and dynamic contact angles. In particular, we compare droplet growth on smooth surfaces and planar microfluidic grids of various surface coverages and heights and discuss contact angle characterization. The surface texture is shown to trap liquid in microwells during the stick-and-slip motion of advancing contact lines. Receding wetting dynamics of liquid infused substrates shows similarity with forced spreading on smooth surfaces. Contact angle hysteresis is investigated as a function of surface parameters to better delineate specific wetting behaviors of water and oil on laser-processed surfaces.