(464f) Capillary Alignment of Long Cylinders On Curved Interfaces

When a cylindrical microparticle attaches to a fluid interface, it creates a distortion owing to its wetting boundary conditions which changes the area of the interface.  If the interface is curved, the interface area, and hence the capillary energy of the system, depends on the particle alignment and location.  In prior work, our group has shown that microcylinders with moderate aspect ratio (L/2R~3; L and R denoting the particle length and radius, respectively) align with their major axes along one of the principle axes of the interface and migrate along paths defined by the curvature gradients to regions of high curvature.  This alignment and migration minimizes the capillary energy.  Here, we show that the preferred orientation of microcylinders changes with aspect ratio; long cylinders prefer to orient perpendicularly to short cylinders and migrate to high curvature zones. More complex behavior is also observed: long cylinders often deviate from simple paths traced by curvature gradients, and can align their major axes at some angle to the principal axes of the interface. We discuss these observations in the context of the excess area of the distortion field around the particle.