The deposition of colloidal particles from liquid droplets on solid substrates is an attractive patterning technology for fabricating biological, electronic or optical devices. One current limitation is the difficulty to achieve uniform patterns during solvent evaporation because the particles tend to deposit along the droplet periphery resulting in a ring-like morphology, known as the coffee-ring effect. Recently the origin and the modeling of the coffee ring effect have stimulated a lot of work but its suppression remains an important challenge in applications.
Here we describe a new method based on bottlebrush polymers for inhibiting the coffee ring effect in colloidal suspensions. The bottlebrush polymers we use consist of a highly charged polyelectrolyte backbone and hydrophilic pendant chains densely tethered to it. When added at extremely low concentrations to colloidal mineral suspensions like calcium carbonate, bottlebrush polymers totally suppress the coffee ring effect and produce very uniform patterns free of defects. We will analyze the new mechanism which is at the origin of coffee ring inhibition by bottle brush polymers and discuss the generality of our results for other colloidal suspensions.