Researchers at the Raman Research Institute (RRI), an autonomous institute of the Department of Science and Technology (DST), have been able to accurately predict the exact time of the emergence of the first crack in aged clay and blood — a finding that can aid in the diagnosis of conditions like anaemia.
The study can also help in forensics and improving the quality of paints used for coatings.
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Researchers studying material science at the RRI proposed a relation between the time of emergence of the first crack, fracture energy — which is the sum of the plastic dissipation and the stored surface energy — and the elasticity of the drying clay sample which can help predict the first crack.
They used the theory of linear poroelasticity, where they estimated the stress at the surface of the drying sample at the time of crack onset.
Linear poroelasticity is a theory for porous media flow that describes the diffusion of water (or any mobile species) in the pores of a saturated elastic gel.
The team equated the stress with Griffith’s criterion which states that a crack will grow when the energy released during propagation is equal to or greater than the energy required to create a new crack surface.
The research, published in the journal Physics of Fluids, detailed that the relation thus obtained was validated by performing a series of experiments. They further said that the same scaling relation worked for other colloidal materials such as silica gels.
“This correlation can be useful while optimising material design during product development. We can apply this knowledge and suggest tweaking in the material composition at the time of manufacturing of industry-grade paints and coatings so that they can have better crack resistance and improve the product quality,” said Professor Ranjini Bandyopadhyay, head of the RheoDLS lab and faculty at the Soft Condensed Matter group at RRI.
In the study, the team used Laponite — a synthetic clay with disk-shaped particles sized 25-30 nanometres (nm) and one nm in thickness.
They created multiple Laponite samples with increasing elasticities, which were then dried at temperatures ranging from 35 to 50 degrees Celsius in a petri dish.
The samples took between 18-24 hours to dry completely and the rate of evaporation and elasticity were measured for each sample. As water evaporated from the Laponite samples, the particles rearranged and stresses developed on the surface of the material.
Higher sample elasticity indicates a better ability of the sample to deform under the influence of these stresses.
It was also noted that the cracks started developing first at the outer walls of the petri dish and later progressed inwards. Later, networks of cracks developed as the sample aged (passing of time).
