There was a lot of speculation but what they know is that there are lots of texture with leaf.
Whet they were trying to do is basically create this effect in the lab. But to make the water repel really well was something that they were missing in the lab and that was the vibration because usually the leaf stands really alone on the stem. So there are a lot of vibrations.
So to make vibration happen in the lab... they went to RadioShack and then the vibration happens then.
All you need is 60 hertz