Abstract

When a colloidal dispersion of rigid particles is spread as a film and dried, a number of transitions occur: The particles consolidate at an edge and a solidification front is seen to traverse laterally across the film. This is closely followed by an array of cracks, with well-defined crack spacing.

This talk will concentrate on why the cracks develop and how they propagate. The driving force for cracking is the capillary pressure, generated during the drying process. The resistance to cracking is the material fracture toughness, which transitions from a low value in the fluid to a final value in the fully developed solid. We show a method of measuring the film fracture toughness using confocal microscopy. It is found to scale with the particle size to the power of minus 0.8. In addition films created with low evaporation rates display higher fracture toughness.

Finally some recent work on the drying of polymeric colloids into gloves will be discussed and a process model to minimise energy usage will be introduced.