Droplets Speeding on Surfaces

How fast a droplet will spread on a solid surface depends on the surface tension gradient and the wettability. The temperature dependence of the surface tension is exploited in a so-called Marangoni flow, but capillary forces can counteract this type of flow. Wasan et al. highlight the report by Danielet al., who have devised a method for harnessing the capillary flow such that it enhances the Marangoni flow. They achieve droplet speeds of up to 1.5 meters per second. The concept may be of interest in applications involving coatings, adhesion, and heat transfer.