Pattern transition and sluggish cracking of colloidal droplet deposition with polymer additives

Drying of colloidal droplets often develops versatile depositions. We study the drying deposition of both colloidal droplets containing silica nanoparticles and the silica colloidal droplets with polyethylene oxide (PEO) additives. We focus on the effect of polymer additives on the deposition formation and the cracking dynamics by using in-situ microscope observation. With PEO additives, a transition from ring-like deposition to uniform deposition is observed, and the cracking dynamics is greatly reduced. The PEO additives enhance the adsorption of particles at the air-water interface, thus forming the network structure at the interface which blocks the outward capillary flow. This contributes to the uniform deposition. Meanwhile, the multi-distribution of the aggregates size enhances the non-homogeneity of the drying film and consequently results in multi-nucleation of cracks. This reduces the stress accumulation that drives the crack propagation and may be responsible for the sluggish cracking dynamics.