When a droplet hits a surface

Understanding how droplets impact surfaces is important for a huge range of different applications. These range from spray painting, inkjet printing, fertiliser application and rainfall to crime-scene blood-splatter analysis and hygiene situations (men’s urinals being a familiar example). High speed movies show that when droplets hit surfaces fast enough, they often splash, emitting a corona of new, tiny droplets on impact.

However, Rob Style (Oxford Mathematics) and Alfonso Castrejon-Pita (Oxford Engineering) noticed that if you drop a droplet on a soft surface, the splashing seems to disappear. They were curious to know if they could use this to develop an easy way to make splash-proof surfaces. So, over the summer, they joined up with Oxford Mathematics undergraduate Chris Howland to carry out experiments in the Mathematical Institute's new experimental facilities, and in Engineering. Chris performed a range of experiments which involved filming impacting drops using a high-speed camera at up to 60,000 frames per second. These conclusively showed that the softer a surface, the better it is at preventing splashing. 
 
A full description of the work can be found in Physical Review Letters. If you are interested in learning more, Chris’s prize-winning poster (the best vacation bursary poster in the Division this year) is currently on display in the Mathematical Institute in Oxford.