Stress Relaxation of Drying Colloids

Stress relaxation during the drying of coatings is of interest due to its importance in the thin film-formation process that dictates the final properties of coatings. Using drying colloidal suspensions as a model system, this study examines how stresses in the colloidal matrix relax when particles are compacted during uniaxial drying in a microfluidics. Microscopic oil droplets co-suspended in the colloidals are used as probes for local stresses and strains as these droplets are deformed by the changing matrix of particles. Balance of the interfacial stress of the oil in the colloids and the stress produced by the compacting colloids dictates the shape evolution of the droplets. The evolution of the deformations of multiple droplets is recorded by confocal fluorescence microscopy. Images of the time evolutions of the droplet shapes and the positions of fluorescent tracer particles nearby the droplets are analyzed by digital image correlation. The talk will address questions on the roles of the viscous damping, interfacial tension between the oil and colloidal matrix, the anisotropy of the strain and stress distributions and the mechanical properties of compacting colloidal particles before the coating is fully dried.