Drying of colloidal droplets on superhydrophobic surfaces

Recent research on the flow patterns during the drying of droplets of solutions or suspensions has revealed a characteristic flow of dissolved or suspended material to the droplet periphery to produce the ‘coffee ring’ phenomenon. This effect was used to make ceramic well-plates by spontaneous manufacturing. Here we demonstrate that when a colloidal droplet dries on a superhydrophobic surface, the effect is rather different. Evaporation from the region adjacent to the three phase line becomes so restricted that the interior flows, and hence the final destination of particles, changes and the characteristic bowl-shape becomes inverted.

The upside-down relic of a droplet of alumina suspension that has dried on a superhydrophobic surface: instead of an upward facing bowl produced on a wetting surface, a downward facing bowl is produced.Figure optionsDownload high-quality image (56 K)Download as PowerPoint slideResearch highlights
► We explore the morphology of colloidal drops when they dry.
► When the contact angle is low, an upturned bowl forms.
► When the contact angle is high (e.g., 150–160°) the bowl is inverted.