Researchers Develop Precise Method to Predict Crack Formation in Drying Clay and Colloidal Layers

The researchers investigated the desiccation process in clay, a critical material in soil and paint formulations, and extended their study to similar colloidal layers like blood and silica gels.

Researchers at the Raman Research Institute (RRI), an autonomous institute under the Department of Science and Technology (DST), have made groundbreaking advancements in predicting the exact timing of crack formation in drying clay and colloidal materials. Their findings have significant implications for diverse fields such as disease diagnosis, forensic science, painting restoration, and the manufacturing of crack-resistant coatings. The study has been published in the journal Physics of Fluids.

Predicting Crack Formation: The Methodology

The researchers investigated the desiccation process in clay, a critical material in soil and paint formulations, and extended their study to similar colloidal layers like blood and silica gels. These layers crack due to drying-induced stress, which has profound applications ranging from anemia diagnostics via blood droplet analysis to optimizing paint durability.

The team proposed a mathematical relationship between:

1. Time of crack emergence
2. Fracture energy (sum of plastic dissipation and stored surface energy)
3. Elasticity of the drying material

This model, derived using the theory of linear poroelasticity, estimates stress levels on the drying material's surface and matches them with critical stress thresholds described by Griffith’s criterion. Validation experiments were conducted using Laponite, a synthetic clay with highly uniform disk-shaped particles.

Key Findings

Elasticity and Temperature Effects: Higher elasticity in a material correlates with faster crack emergence as the material is less able to dissipate stress. Drying samples at higher temperatures (35-50°C) expedited solvent loss, increasing stress buildup and reducing the time to crack onset (10-14 hours).

Spatial Cracking Pattern: Initial cracks appeared along the outer edges of the drying material, progressing inward as the sample aged. Networks of cracks formed over time, influenced by particle rearrangements and drying stresses.

Material Optimization: By adjusting variables such as material concentration, salt content, or pH, researchers demonstrated the ability to fine-tune elasticity and delay crack formation. This has applications in designing more resilient coatings for spacecraft, medicine capsules, and industrial-grade paints.

Applications Across Fields

The research highlights how understanding the mechanics of crack formation can be utilized in:

• Medicine: Analyzing drying patterns of blood droplets for disease diagnosis.
• Forensics: Studying drying layers for clues at crime scenes.
• Art Restoration: Predicting and preventing crack propagation in aged paintings.
• Paint and Coating Manufacturing: Enhancing product durability by minimizing cracks through material optimization.

Implications for Extreme Environments

Clay's natural heat resistance and insulating properties make it suitable for high-temperature applications like spacecraft coatings. This study provides insights into maintaining the structural integrity of clay-based materials under extreme conditions, simulating diurnal temperature fluctuations that mimic real-world scenarios.

Future Prospects

Lead researcher Professor Ranjini Bandyopadhyay, head of the RheoDLS lab at RRI, emphasized the utility of their findings for material design in industrial applications: “This correlation can be useful while optimizing material design during product development. By tweaking the material composition, industry-grade paints and coatings can achieve better crack resistance and product quality.”

The study’s first author, Vaibhav Parmar, highlighted the broader significance: “Understanding drying-induced cracks is imperative to geophysical, mechanical, and material science. The findings are particularly useful for delaying cracks in controlled environments like coatings on spacecraft or medicine capsules.”

This pioneering research opens new avenues for predictive material science and real-world applications where durability and resistance to cracking are critical.