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
Curvature of Capillary Bridges as a Competition between Wetting and Confinement
Authors: David J. Broesch,Filip Dutka, and Joelle Frechette
Langmuir, Article ASAP
We consider the shape evolution of non-axisymmetric capillary bridges in slit pore geometry as the pore height is increased at constant volume. Experiments and finite element simulations using Surface Evolver have shown that as the height of the pore is increased the mean curvature of the bridge, and hence Laplace pressure, changes its sign from negative to positive. Here we propose an intuitive explanation of this surprising phenomenon. We suggest that it is the balance between the confinement and the wetting properties of the supporting strips that causes the change in sign of the Laplace pressure. The theory proposed relies on three simple approximations, which are tested individually, and is in good agreement with experiments and simulations in the regime where the curvature transition from negative to positive takes place. Theoretical arguments take into account only the wetting properties and geometry of the system (the width and height of the pore). Along with the formula for the curvature, we derive also a relation for the pinning angle of the capillary bridge, which is also verified experimentally.