We study migration of 10 micron PS microspheres at fluid interfaces with well-defined curvature fields. The particles migrate along curvature gradients to sites of high curvature.  Particles  “sense” the host interface shape via the contact line boundary condition, which can, in principle, either obey an equilibrium contact angle or be pinned.   We derive capillary energies for both cases. For pinned contact lines, particle roughness makes a nanoscopic quadrupolar distortion in the interface, which couples to the curvature field. The resulting capillary energy is linear in the deviatoric curvature. For equilibrium contact lines, the capillary energy is negligible. We compare the energy dissipated by particle migration to prediction, finding excellent agreement with the expression for pinned contact lines.  This phenomenon provides a macroscopic read-out for nanometric surface roughness.

Capillary migration of spheres on curved fluid interface

249th National Meeting (2015)

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