Why does water bead up on a waxed surface? Why does ink form a good image on some paper but runs and smears on others?

In this module we delve into the dynamics of surface energy/ wetting. Many forces come together to affect whether a drop of liquid might spread out onto a surface instead of beading up and rolling away. Surface texture plays a central role, as you might expect, but it is only part of the answer. We introduce the concepts of “surface tension” and “hysteresis” and how these various characteristics help us predict whether a surface will be “hydrophilic” or “hydrophobic.” We also examine the surface texture parameters that help to quantify the wettability of a given surface. And, lastly, we show how researchers and engineers in various fields are modifying surface textures in order to achieve a desired wettability—whether it’s to keep your windshield clear of rain or reduce the smudges on your phone.

This is Module 8 of the Surface Texture and Tribology Short Course. The full course is available on udemy, or you can select the individual course modules of interest to you. Enter "surface roughness texture tribology" in the udemy search bar to browse the full course and modules.