New waterproofing material developed from Fly Ash by IIT-H

IIT – Hyderabad has developed a new waterproofing material that is cost-effective and smoother finish, which is made by coating Fly Ash, with stearic acid. Though the waterproofing material is yet to be tested more for its mechanical and chemical durability, this experiment could be a new way of looking at waterproofing. The new waterproofing material is also easily to apply, as all one needs is an adhesive to apply this waterproofing material on a surface.

The Fly Ash is a waste by-product from coal-based thermal power plants while stearic acid is a surfactant, a surfactant is a substance which when dissolved in a liquid; reduces the surface tension of that liquid. Thus even though Fly ash responds well to water, it turns out to be water-repelling when coated with stearic acid. The composition of stearic acid consists of a hydrophilic part – the head, and the hydrophobic portion – the tail. The head of the stearic acid binds to the fly ash particles, making the water-repelling tail remains free, and since the number of free tails is manifold, the stearic acid makes the fly ash surface water repellant. The size of Fly Ash varies in size from 100 nanometres to a few microns, on the basis of the particles chosen, different roughness in the surfaces of the fly ash is produced.

There are two types of naturally occurring patterns that the stearic acid-coated fly ash could be made to behave in by simply varying the surface roughness of it, either the rose petals and the lotus leaves. Both the patterns have distinct qualities, the rose petal repels the water and at the same time also makes sure that the water droplets adhere to it making sure that the water droplets will not fall down when inverted. In the case of lotus leaves, the water droplets fall off easily. 

Dr. Atul Suresh Deshpande, IIT-Hyderabad’s Department of Material Science and Metallurgical Engineering explained the distinct properties saying, “ When we used particles of more or less uniform size, the inter-particle space is more and water penetrates and sticks to the surface like in the case of a rose petal and remains adhered to the surface even when we tilted it to 90 and 180 degrees”. Dr, Atul Suresh Deshpande is also the corresponding author of a paper publishes in Chemistry Select. The topography of the waterproofing material also changes when different particles sizes are used as smaller particles fill the gap between the large ones, which leads to a tight packing with minuscule gaps between particles. Dr. Mudrika Khandelwal, IIT Hyderabad and Co-author of paper said, “Air pockets tend to form when the gap between particles reduces making it difficult for water to get into the gaps. Water droplets are suspended on top of the air pockets and so has less adhesion to the surface. So when the surface is tilted slightly (5 degrees) the droplets tend to roll off easily.” 

According to Urbashi Mahanta, A Ph.D. student from IIT Hyderabad and first author of the paper said that they,” By using a combination of stearic acid and surface roughness we were able to achieve superhydrophobicity (where the water contact angle is more than 150 degree).” She said that a simple process of particle distribution was used to achieve the two types of hydrophobicity. On increasing the drying temperature from 60 degrees to 80 degrees, the hydrophobicity in both surface types increased. The melting point of stearic acid being over 6 degrees, on providing 80 degrees, it melted achieving a better coverage which eventually resulted in a smoother surface. Also due to the smooth nature of the surface, it has proven to be easily cleaned.    

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