Why water droplets stick to rose petals?

 
By ESHA SEKHAR
Published: Saturday 31 May 2008

DownToEarthobserving rose petals with water droplets glittering in the sunshine, some researchers in China wondered why the water droplets stuck to the surface of the petal. Even when they turned the flower upside down, the droplets didnt fall off. We work on the interaction of solid surfaces with water, including natural surfaces. When we saw rose petals with water droplets on them, we picked some petals for study, said Lin Feng, the lead author from the department of chemistry, Tsinghua University,China.

Research followed observation and what has come to light is the petal effectthe physical basis of a rose to hold on to water droplets. This hints at its use in adhesives, paints and fabrics, says the study published in the American Chemical Societys journal, Langmuir (Vol 24, No 8). It is the opposite of the lotus effect discovered earlier, which says that water droplets can roll off easily from lotus petals.

Rose petals have tiny outgrowths on them that are not visible to the naked eye. Called micro-papillae, these outgrowths give the petals sufficient roughness, with two fallouts. One, the petals become highly water repellent, a property called superhydrophobicity, and two, it makes them adhesive.

The micro papillae form a seal with water droplets allowing them to cling to the surface of the petal. The experiment was conducted by Feng, along with scientists of the Chinese Academy of Sciences, Jilin University, Changchun, and the National Center for Nanoscience and Technology, Beijing. The researchers also developed a synthetic petal to test for varied applications.

According to Lin, the synthetic petals, which they used as moulds to make polymer films, could be used for paint coatings, functional fibres and microfluids. The most exciting application, she says, is in a laboratory as lab-on-a-chip devices. Surfaces could be used to transfer water droplets with the risk of contamination. This is a pre-requisite for analyzing micro samples.

Ashutosh Sharma of the Department of Chemical Engineering, iit Kanpur, says the material can be used to make water-retaining surfaces. He is confident of its use in other areas after further research is done.

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