High-Speed Photography Reveals Secrets of Splashing

Daniel S. Burgess

Harold E. "Doc" Edgerton's stroboscopic photographs of the "coronet" splash formed by a droplet of milk falling onto a saucer have become iconic. Now physicists at the University of Chicago have found that the formation of the splash depends on the pressure of the surrounding gas, a finding that may have applications in fuel combustion, ink-jet printing, spray drying and industrial washing.

They used a Phantom v7.0 CMOS camera from Vision Research Inc. of Wayne, N.J., operating at 47,000 fps to image drops of three different liquids -- each 3.4 ±0.1 mm in diameter -- under four gases at pressures between 1 and 100 kPa. They observed that there exists a threshold pressure that scales with the viscosity of the liquid and the molecular weight of the gas, below which splashing does not occur. The image illustrates the behavior of ethanol droplets impacting a smooth glass substrate under the noted pressures of air.