The Coffee-Ring Effect on 3D Patterns: A Simple Approach to Creating Complex Hierarchical Materials

The coffee-ring effect can be troublesome or beneficial in many surface coating and patterning technologies, prompting an extensive investigation into understanding its underlying mechanism. Although valuable insights are available on drying of polymer solutions on planar surfaces, such information is lacking for 3D-patterned substrates. Here, the experimental realization of the coffee-ring effect of a polymer solution on topographical surfaces is reported. Interestingly, the results indicate that, following the capillary flow, the polymer is divided between multiple contact lines on the 3D features and around the base. Therefore, for a proper spacing between the 3D patterns, it is demonstrated that the polymer deposit can be limited to the 3D structures, leaving the base unoccupied. This superposition property is then exploited to fabricate complex hierarchical materials with selective wrinkling on the 3D features, by simply drying a polymer solution on them and, subsequently crosslinking the polymers using plasma.