Some surfaces repel water almost perfectly. Think about the feet of a water strider.
But rare are the surfaces, natural or manmade, that can repel oily, organic liquids such as gasoline. In part because such liquids have very low surface tension - a measure of a liquid's tendency to bead up in discrete droplets - these fluids spread out over almost any surface, which is why a few drops of motor oil will quickly coat an entire pond with shimmering hues.
Now, engineers at the Massachusetts Institute of Technology have figured out enough of the mathematics, chemistry, and micro-geometry of repellent surfaces to design new ones that can keep organic liquids from soaking in or spreading out. Robert E. Cohen and his colleagues calculated what it would take for a surface to have just the right degree of roughness - and the right amount of finer roughness on top of that - so that even very-low-surface-tension liquids bead up like water on the hood of a newly waxed car.
The Air Force, which supported the work, published in the journal Science, hopes that such materials will be useful for picking up jet fuel splashes, letting the fuel bead up for an easy cleanup rather than soaking into equipment. No word on whether they can be made into ties, an application that dry cleaners are sure to oppose.
