In situ study of mass loss, shrinkage and stress development during drying of cast colloidal films

During constrained drying of binder-assisted colloidal coatings on rigid substrates, drying stress-induced defects such as cracks and warpage can often be observed due to the lateral confinement of the film by the substrate. The purpose of the current work is to understand the origin of these drying defects and to develop strategies for their avoidance by the adjustment of slurry composition or processing parameters. In this paper, the time-dependent drying behavior of colloidal ceramic coatings was studied in situ by observation of mass loss, drying shrinkage and drying stress by different methods, such as transparent substrate deflection and beam deflection methods. The stress development and the critical moment, at which cracks form, were investigated in films of different compositions with respect to solvent, particle size, binder and plasticizer. The origins of the measured differences in drying shrinkage, crack formation as well as residual stresses after drying were discussed.