Up until now, fly ash had limited benefits. There have been attempts to utilise it in various forms, but they too have resulted in scarce use of the industrial waste product. It is in this context that the research by a team from Indian Institute of Technology, Hyderabad, (IIT-H) holds significance.
They have used fly ash to develop water-repellent structures that mimic the characteristics of lotus leaves and rose petals. Such ‘super hydrophobic’ structures have significant industrial 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.
The practical implications of the work by the IIT-H team are compelling. Not only is the water-repellent product much cheaper than other super hydrophobic coatings that have been developed so far, but serves towards upcycling an industrial waste material – fly ash – into a useful product, which serves the double purpose of extra revenue generation and waste management.
The research was jointly undertaken by Mudrika Khandelwal and Atul Suresh Deshpande, Department of Materials Science and Metallurgical Engineering. Their research paper, co-authored with Urbashi Mahanta, was recently published in the reputed peer-reviewed journal Chemistry Select .
“The water-repellent properties of the lotus leaf and rose petal have been known for a long time, and scientists have explored ways in which these properties can be mimicked for various applications. Mimicking natural structures for engineering applications is not easy. To artificially replicate a natural phenomenon, scientists must understand the relationship between the natural element and the purpose it serves,” said Dr. Khandelwal.
While both lotus leaf and rose petal are water repellent, drops slide off the lotus leaf carrying with them any dirt and debris on the leaf, but drops stick to the rose petal and do not fall even when the petal is inverted. This difference arises from differences in the structures. The surface of the rose petal consists of microstructures that have larger spacing, and a smaller density of nanostructures than the surface of a lotus leaf.
“We have used an inexpensive material, fly ash, to obtain hydrophobic surfaces with tailorable water adhesion behaviour. The particle size of fly ash is between 100 nanometres and a few micrometres, a size range that is suitable for generating rough surfaces that are hydrophobic. However, fly ash itself is not water repellent, and therefore, we coated stearic acid on fly ash particles,” said Dr. Suresh Deshpande.
“Using this surface modified fly ash particles, we were able to obtain surfaces with different adhesion properties. Whether the water drops rolled off (lotus leaf effect) the surface coated with fly ash or stuck to the surface (petal effect) depended on when the stearic acid was coated on 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 results in the rose petal effect,” explained Dr. Deshpande.
Dr. Khandelwal said, “Our method of producing water-repellent surfaces is quick and highly scalable as it does not require any sophisticated instrument”. The synthesis process is so simple that even an untrained individual can apply it to obtain super hydrophobic surfaces at a low cost.
Dr. Deshpande added that the super hydrophobic coatings produced using fly ash can be used to protect concrete structures from rain and moisture-induced damage. In addition, these materials can be used for water harvesting applications.
