We seek to harness interfacial phenomena to achieve external, reversible, and local control of wetting and adhesion properties. The large surface to volume ratios provided when devices are shrunk to the micro- and nanoscale create particularly exciting opportunities for exerting control via tunable surface interactions.
To achieve this goal, we explore two separate avenues for the control of surface and interfacial properties: control of electrostatic interactions and design of surface structure. The importance of electrostaticsis approached by studying the nanoscale limits of electrowetting on dielectric, the design of responsive films that can be employed to move drops, and the use of surface charge as a means to control the assembly of nanoparticles at the oil-water interface. Our efforts in the control of surface structure have been focused on the understanding of the mechanisms for the adhesion of tree frogs under flooded condition, and on the importance of partial contact line pinning on the morphology of capillary bridges
Coupled effects of applied load and surface structure on the viscous forces during peeling
Authors: Charles Dhong, Joelle Frechette
Tree frogs are able to take advantage of an array of epithelial cells in their toe pads to modulate their adhesion to surfaces under dry, wet, and flooded environments. It has been hypothesized that the interconnected channels separating the epithelial cells could reduce the hydrodynamic repulsion to facilitate contact under a completely submerged environment (flooded conditions). Using a custom-built apparatus we investigate the interplay between surface structure and loading conditions on the peeling force. By combining a normal approach and detachment by peeling we can isolate the effects of surface structure from the loading conditions. We investigate three surfaces: two rigid structured surfaces that consist of arrays of cylindrical posts and a flat surface as a control. We observe three regimes in the work required to separate the structured surface that depend on the fluid film thickness prior to pull out. These three regimes are based on hydrodynamics and our experimental results are compared with a simple scaling argument that relates the surface features to the different regimes observed. Overall we find that the work of separation of a structured surface is always less than or equal to that for a smooth surface when considering purely viscous contributions.