Imaging strain field near the tip of a propoagting crack in drying colloidal films

Drying-induced cracking is commonly seen in colloidal coatings like paints and is also a major limiting factor in developing solution-processed functional nanoparticle films. Due to its non-equilibrium nature, it is also challenging to directly study the mechanics, i.e. stress and strain, of cracks formed in those films. In this work, we use video microscopy to track a propogating crack in a colloidal nanoparticle film over the whole drying process, while quantifying microscopic strain field near the crack tip using fluorescent tracer particles. Our work will shed light on the underlying fracture mechanics that governs the cracking behaviors in drying colloidal films and can also provide a general tool in studying mechanics of other soft matter systems.