Marangoni flow alters wetting: Coffee ring and superspreading

Colloidal nano altered wetting is an everyday phenomenon with various applications. It occurs when an aqueous colloidal droplet is placed on a wet solid and evaporates with a pinned contact line (to form a shape similar to a coffee ring) and when a 'superspreader' is placed on a partially wet solid surface with an unpinned contact line. This article reviews recent advances on the mechanisms behind these two phenomena. For the coffee ring phenomenon, besides the evaporation flow, the thermal and solutal Marangoni flow are critical to the radial flow as they carry solutes from the droplet's interior to the contact line. The particle self-assembly into a layered structure at the droplet edge involves particle structuring under confinement and the stagnation flow. While superspreading is not fully understood, it is proposed that the Marangoni flow plays an essential role in superspreading.

Automated summary

This article reviews recent advances on the mechanisms behind colloidal nano altered wetting phenomenon, focusing on the importance of thermal and solutal Marangoni flow in the coffee ring phenomenon, as well as the role of particle self-assembly and Marangoni flow in superspreading. While the exact mechanisms behind superspreading are not fully understood, it is suggested that Marangoni flow plays a crucial role in this process.