Researchers find ways to use fly ash to waterproof products

A recent scientific study as found ways to turn fly ash, a waste product from power plants which cause air and land pollution, into useful products like paints, textiles coatings etc.

Researchers from the Indian Institute of Technology Hyderabad (IIT-H) have used this waste product to develop water-repellent structures that mimic the characteristics of lotus leaves and rose petals.

Such ‘super-hydrophobic’ (super water-repellent) structures have potential applications such as anti-fouling paints, anti-sticking surfaces for antennae, self-cleaning coatings for automobiles, stain-resistant textiles and anti-soiling architectural coatings, among others.

This research was jointly undertaken by Mudrika Khandelwal and Atul Suresh Deshpande, Department of Materials Science and Metallurgical Engineering, IIT-Hyderabad. Their research paper, co-authored with Urbashi Mahanta, was recently published in the journal Chemistry Select .

According to Deshpande, the super-hydrophobic coatings produced can be used to protect concrete structures from rain and moisture-induced damage. They also find application in water harvesting.

Not only is the water-repellent product much cheaper than other super hydrophobic coatings developed so far, but it also serves towards up-cycling an industrial waste material — fly ash — into an industrially useful product, which serves the double purpose of side-revenue and waste management, the IIT researchers said.

The method explained

Explaining the work, Mudrika Khandelwal said, “The water repellence properties of the lotus leaf and rose petal have been known for a long time, and scientists have explored ways in which these structures can be made artificially for various applications. Mimicking natural structures for engineering applications was not easy. In order to artificially replicate a natural phenomenon, scientists must understand the relationship between the natural structure and the purpose it serves.”

While both lotus leaf and rose petal are water repellent, drops slide off the lotus leaf, carrying with them any dirt and debris, but stick to the rose petal even when it is inverted. This difference arises from the differences in the structures.

The surface of the rose petal consists of micro-structures that have larger spacing, and a smaller density of nano-structures than the surface of lotus.

Attempts to replicate the super hydrophobicity of nature have involved altering the water adhesion behaviour of surfaces. Existing methods use costly materials or sophisticated instruments or suffer from scalability issues. This prompted the IIT Hyderabad researchers to look at cheap materials. They stumbled on fly ash, a waste and inexpensive material to obtain, to make different surfaces hydrophobic.

“The particle size of fly ash is between 100 nanometres to a few micrometres, which is suitable for generating rough surfaces that are hydrophobic. However fly ash itself is not water repellent, and therefore, we (researchers) coated stearic acid on the fly ash particles,” they explain.

Using these surface-modified fly ash particles, the researchers were able to obtain surfaces with different adhesion properties. Whether the water drops rolled-off (‘lotus-leaf effect’) surfaces coated with the fly ash, or stuck to the surface (‘petal effect’) depended upon when the stearic acid was coated on the fly ash particles.

“Coating the fly ash particles with stearic acid before depositing the fly ash on the surface lead to the ‘lotus-leaf’ effect, whereas depositing fly ash particles and then coating them with stearic acid resulted in the ‘rose-petal’ effect,” said Deshpande.

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