Fluid and Particulate Motion in Printed Drops

This project will study the fluid motions within drops deposited by inkjet printers, through the use and development of numerical methods and mathematical models of colloidal suspensions during drop deposition. In particular we are interested in understanding the fluid and suspended particle motions in various scenarios including the impact, spreading and evaporation of single drops on non-porous solids, coalescence of consecutive drops to form continuous tracks, and the evaporation versus imbibition of drops deposited on porous substrates. Particle migration can lead to the so-called “coffee-ring” effect where the particles tend to collect at the contact point forming a ring of high particle concentration at the outer edge of the drop. This feature is generally undesirable in printing, and a number of experimental studies have demonstrated that it possible to overcome this phenomenon using mixtures of solvents. However, at present there is no theory that is able to explain this motion.