Capillary bridges across heterogeneous surfaces

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We investigate the role of partial contact line pinning in the morphological evolution of capillary bridges. Capillary bridges between solid substrates are critical to a multitude of industrial and natural processes. For example, they provide the cohesion force necessary to give structure to wet granular materials such as sand castles. In confined geometry fluid bridges formed via capillary condensation are responsible for unwanted adhesion in microelectromechanical systems (MEMS). With the advent of patterning and lithography, surfaces can be created with heterogeneous physical or chemical boundaries that pin the triple contact line of fluids. Pinning of the triple contact line on a surface alters the shape of a capillary bridge and allows for the design of surface patterns that lead to pre-determined capillary forces or bridge morphology. While the number and complexity of surface patterns that can bound capillary bridges is virtually unlimited, even simple cases that rely on high levels of symmetry have shown promise in micro & nanoscale systems. Our experiments and numerical simulations aimed at characterizing the morphology of capillary bridges in slit pore geometry have led to the counterintuitive observation that Laplace pressure goes from negative to positive as the height of the capillary bridge is increased. 

 Papers:

From Concave to Convex: Capillary Bridges in Slit Pore Geometry (Langmuir)

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