Watching ink dry.

The inkjet printing of inks containing dispersed particles, such as binders and pigments, is a complex process that involves a combination of drying, wicking, coalescence and film formation events. The combination of these phenomena governs not only the dynamics of dyring and ultimate consolidation of a printed droplet, but also the quality of the final printed coating. Understanding the dynamics of this process, in particular the internal dynamics of the particle-containing droplets, has remained highly challenging. This is especially the case for printing on porous substrates, where the ratio of evaporative and substrate-driven solvent loss sets the drying and film formation process. The incompleteness of our knowledge of these processes is a major hurdle in establishing robust inkjet printing processes and the development of new sustainable inks free of organic solvents. In this project, we will study inkjet printing with high spatiotemporal resolution, using a unique combination of a new imaging method, Laser Speckle Imaging, and a custom-made printing instrument. This will enable us to study in detail the drying, porous wicking, coalescence and film formation within picolitre droplets with micrometer and sub-millisecond resolution. In this approach, we aim to deepen our understanding of inkjet printing and study the effects of surface porosity, ink formulation and environmental conditions on the deposition process and the properties of the final coating.