title: Curvature of capillary bridges as a competition between wetting and confinement.
abstract: 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.
authors.affiliation: Chemical and Biomolecular Engineering Department, Johns Hopkins University , Baltimore Maryland 21218, United States.
authors.forename: David J
authors.initials: DJ
authors.lastname: Broesch
authors.forename: Filip
authors.initials: F
authors.lastname: Dutka
authors.forename: Joelle
authors.initials: J
authors.lastname: Frechette