The Emergence of Rigidity in Desiccated Granular Materials

Granular materials on planetary surfaces are subjected to repeated cycles of wetting and desiccation. These processes influence soils, sediments, and regolith. Desiccation often increases rigidity in granular materials even when fully dry. We examine this phenomenon using 100–300-micron spherical glass beads, varying particle cleanliness, drying conditions, and solvent polarity. The strength of dried samples was tested using a robot arm with a force sensor. Initial packing fraction was crucial for reproducible cluster strengths. Water-dried samples remained the most rigid even after extensive cleaning, revealing a fundamental glass-water cohesion. When uncleaned samples were placed under high temperature and pressure (autoclave), they became extremely strong, suggesting residual contaminants act as a potent binder. The rigid cluster structure depended on drying time, with the top surface layer often delaminating with slow drying. Our results show that granular contacts formed through desiccation develop significant "sticky" forces due to physical or chemical changes left by the evaporated liquid, a potential mechanism by which natural earth materials are shaped by their environment.