Coffee-ring formation through the use of the multi-ring mechanism guided by the self-assembly of magnetic nanoparticles

The control of the mechanism leading to the appearance of the ring-shaped stains from the dried liquid colloidal droplets has been the subject of intense studies over the last 25 years. This stems from the immense significance of this effect for technological applications. One of the key open topics in this field is the emergence of a regular multi-ring deposit from the dried droplet. Here, we show that magnetic nanoparticles in a drying magnetic liquid droplet can self-assemble into a multi-ring deposit structure, and even more importantly, a magnetic field can be turned on to control the underlying processes. The magnetic liquid is prepared as an aqueous suspension of Fe[Formula: see text] O[Formula: see text] magnetic nanoparticles stabilized with (3-Aminopropyl)triethoxysilane (APTES) and its droplets are placed on low-density polyethylene (LDPE) film. The results of this work are expected to be very promising in the case of multiple applications including ink-jet printing methods and 2D printed electronics.