Stresses and strains in colloidal films during lateral drying

Cracking and warping during drying are everyday phenomena of great importance, yet the processes that lead to them are still not fully understood. Existing ideas generally focus on the relaxation of capillary tension in the liquid as the driving force for cracking and predict that cracking should occur as the pores drain of liquid. However cracking is observed to occur before this. Recently this approach has been modified to include viscous flow of water through the particle network. An alternative view, based on observations of the height changes that of a drying film, is that when the water-filled network first forms the particles are not in contact, although the material has residual strength and is bonded to the substrate. The strengths and shortcomings of these two approaches are considered by comparison with experimental observations to outline areas of future work. (c) 2007 Elsevier Ltd. All rights reserved.