A carpet of minuscule bumps covered with even tinier ridges makes the dewdrops stick. Image
Ah, roses. Their heady fragrance and delicate petals glistening with dew could soften the hardest heart.
But take a sharper look at the dewdrops. They bead, rather than spread—and that's because the material composing the petal surface doesn't bond well with water.
Yet the droplets don't roll off. What binds them to the petals?
To find out, a team of chemists led by Lin Feng of Tsinghua University in Beijing peered at the petals with a scanning electron microscope. What they saw was a carpet of minuscule bumps covered with even tinier ridges. To confirm that those structures — and not the chemical makeup of the petals — are what grip the water droplets, Feng's team made a plastic cast of the petal surface. As with the original petal, water droplets stuck to the cast, even when it was turned upside down.
It's the texture, then, that does the trick. Texture is also important in the so-called "lotus effect," which causes water to bead up and roll off many plants' leaves and petals, clearing away dust and debris. The difference: on drop-shedding surfaces, the tiny bumps have wax-coated tips and are separated by narrower troughs, so they make less contact with water.
Feng thinks that the rose's waxless "petal effect" might help flowers attract pollinators by holding glistening dewdrops.
Casts like Feng's could be cheaply manufactured, should any commercial uses be found for the unusual properties of rose petals. But romantics needn't worry — even a dozen casts won't convey love messages like the real thing.
The findings were detialed in the journal Langmuir.