Soon, you may not have to agonise over the recurrent chips in your wall paint, if industry takes forward a recent research on the behaviour of constituent particles in a coating.
Karnail B Singh, his guide Prof Mahesh Tirumkudulu evolve formula to derive baseline for the coating
Soon, you may not have to agonise over the recurrent chips in your wall paint, if industry takes forward a recent research on the behaviour of constituent particles in a coating. Chemical Engineering research scholar Karnail B Singh, and his guide, Prof Mahesh Tirumkudulu of IIT Bombay, have evolved a formula to derive the baseline for crack-free coating, whether it is on the wall or on photographic film.
The study, published in May 25 issue of the international journal Physical Review Letters, explores the parameters which control cracking or chipping of any coating. “It’s a basic study of the critical thickness required for any coating to stay crack-free,’’ says Prof Tirumkudulu. The bottom line of our study was to ensure that the layer of coating shouldn’t crack.
Most coatings are made up of tiny particles in a solvent. When the solvent or emulsion evaporates, the constituent particles dry up and concentrate (cluster together). During this process, tensile forces act on the film and if it exceeds a certain value, it cracks.
“We tried to determine the conditions under which it would crack. So, we examined the variables at work such as size of the particles, their rigidity, and the packing, i.e., whether the cluster particles bind loose or closely,’’ says Prof Tirumkudulu.
While most paints are complex - a mix of hard and soft particles with additives, the research examines coatings with only a single type of particle. “We’ve worked on the first step to come up with some sort of a benchmark,’’ he says.
Prof Tirumkudulu’s previous research at Princeton University dwelt on impermeable surface coatings; while his latest work focuses on porous coatings composed of particles of diameters ranging from 0.02 micron to 1 micron (one micron is one-millionth of a metre). Research done by other scholars abroad in 1993, had shown that each surface coating has a critical crack-free thickness above which it could crack but below which it doesn’t.
“How to determine critical thickness was unresolved till now. We have found the properties which influence it,’’ says Prof Tirumkudulu.
Though most wall paints are non-porous, the study will yield an understanding of the interplay of various factors in the phenomenon of cracking. “If you give me the size, rigidity and packing of particles and surface tension in a coating, I can tell you its critical thickness, which can prevent the coating from cracking,’’ says Prof Tirumkudulu. The study, he says, will enable an assessment of whether any paint will form a porous or non-porous film and whether it will crack or not.
What if the critical thickness is too small for the coating to be effective? Prof Tirumkudulu says in a porous coating, one can tailor the particle to push up its critical thickness. “One can increase the radius of the particle, or play with other variables for greater stress strength,’’ he says.
The research could help paint manufacturers optimise their products - it could be useful in fabricating paints and printing media for ink-jet printers, among others. Surprisingly, the pair got no encouragement from leading paint manufacturers in the country. “The entire work has been funded by the Union Government’s Department of Science and Technology,’’ says Prof Tirumkudulu.
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