Experimental investigation on capillary bridge dynamics and adhesive forces in porous structures

The stability and adhesion of capillary bridges are fundamental to processes in diverse fields, from pharmaceutical powder handling and food processing to microfluidics and geophysics. While critical, the evolution of these bridges under the combined influence of evaporation and mechanical traction remains poorly quantified, limiting the predictive accuracy of current models. This study presents an experimental investigation into the complex dynamics of capillary bridges formed between two spherical surfaces under these coupled conditions. A novel experimental facility was designed for the precise, simultaneous measurement of capillary adhesion force and the real-time tracking of the bridge's morphological evolution using water and ethanol as a working fluid. This integrated approach allows for direct correlation between mechanical forces and dynamic geometric changes. Using high-speed imaging and advanced image processing, key geometric parameters, including neck radius, contact angle, and bridge height, were extracted from the axisymmetric bridges. The results reveal that the substrate surface characteristics significantly influence the adhesive force, leading to distinct and predictable behaviors for water vs ethanol. The data empirically validate key theoretical predictions, quantifying the dependence of adhesion force on bridge volume and the inverse relationship with bridge height. Furthermore, fluctuations in Laplace pressure and contact angles were directly linked to transient, evaporation-driven mass loss and traction-induced changes in curvature. These findings offer crucial new insights into the role of fluid–substrate interactions in capillary-mediated adhesion. The comprehensive dataset and analysis provide a robust foundation for refining mechanistic models used to simulate and control particulate systems where capillary forces are dominant.