AsianScientist (Nov. 18, 2025) – Leaves have a coating that repels water and protects them fungal and bacterial attacks. But for farmers, this natural coating is a barrier. When they apply pesticides to protect their crops and plants from pests, half of the pesticides simply run off the leaves.
At the Centre for Nano Science and Engineering at the Indian Institute of Science (IISc), Bengaluru, Rutvik Lathia had been working with liquid marbles — liquid droplets encased in a layer of water-repelling particles — during his PhD. At his advisor Prosenjit Sen’s laboratory, he noticed something unexpected: liquid marbles adhere to water-repellent surfaces better than a bare water droplet. Putting two and two together, the group has proposed using liquid marbles as pesticides in a paper published in the Journal of Colloid and Interface Science.
“This is counterintuitive and interesting,” Lathia, who is now a postdoctoral researcher at the Max Planck Institute for Polymer Research, Mainz, Germany, told Asian Scientist Magazine over email, “as in one of our previous works, we observed liquid marbles bounce faster than droplets” on some surfaces which repel water.
Currently, the pesticide industry is addressing the roll-off problem in various ways. One solution is to use polymers and oils to increase the stickiness of pesticides, but they are harmful to the environment. Another is to use special liquids that help in sticking the pesticides to the leaves but they contain ‘surfactants’, which especially harmful to honey bees. According to the IISc group, liquid marbles provide a biodegradable alternative that is, at the same time, much more efficient at depositing on water-repelling surfaces.
Curiously, the difference between a water droplet and a liquid marble is thin — quite literally — about 35 microns of water-hating material, like glass, separating them. But the thin glass layer seems to be making all the difference. Whereas water droplets spread on a water-repelling surface, they recoil sharply, leaving only about 5 percent deposited.
But the glass particles, which are water-hating themselves, mark the difference in property between simple water droplets and liquid marbles. More than 95 percent of the liquid marbles are absorbed. .
Essentially, the difference boils down to the absence of recoil, which, as Lathia explained, happens because the liquid marbles lose 50 percent of their energy (unlike water droplets) due to their internal structure changing during the collision and the glass particles colliding with each other. The collisions increase friction, similar to how cars blocking the road cause traffic jams.
But glass beads and Teflon, which researchers typically use in the laboratory to produce liquid marbles, are also harmful to the plants. So, the IISc team explored alternative particles that are biodegradable and organic, such as lycopodium and zein (a protein found in corn). They showed that liquid marbles made with these materials are more efficient than those using glass bead coating.
However, adopting the biodegradable liquid marbles to pesticides isn’t easy.
“The main challenge is scalability,” said Lathia. It’s not yet feasible to produce liquid marbles in large quantities at a cost comparable to conventional spraying. Moreover, there is currently no spraying mechanism that can generate liquid marbles with the same efficiency as standard droplet-based systems.
The biggest bottleneck seems to be understanding the science itself: “We still need to study how the particle coating influences pesticide uptake by the leaf,” said Lathia.
That’s not it. The researchers also need to figure out “whether long-term retention of particles affects plant functions such as photosynthesis or gas exchange,” he added.
The team is trying to solve multiple hurdles. One, regarding the manufacturing: they are planning to develop a continuous setup capable of producing large numbers of liquid marbles with controlled size and coating.
Two, they will test nozzle designs that allow liquid marbles to form directly during spraying. “We also aim to identify more sustainable particle coatings: either materials that dissolve rapidly after deposition or coatings that themselves provide pesticidal action,” Lathia said.
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Source: Indian Institute of Science; Images: Pijo/Shutterstock
The study can be found at: Hydrophobic particle coating for enhanced droplet deposition