Emulsions of oil-based pesticides are widely used in agriculture, although they are a major environmental and health hazard because they bounce off plant surfaces due to their hydrophobic nature, resulting in the pollution of water and soil. In a new report, Maher Damak and a team of scientists in mechanical engineering at MIT described an unexpected transition from bouncing to sticking to bouncing, with accelerated impact speed of the droplet. The team highlighted the underlying physics of the phenomenon and demonstrated the process by regulating a careful balance of three time scales: the time of droplet contact, time of oil impregnation and the formation of the oil ridge. They then built a design map to accurately regulate droplet bouncing and oil coverage. The research is now published in Science Advances.