| Popis: |
A small hole etched in the top of a wide microchannel creates a well of surface energy for a confined drop. This produces an attractive force ${F}_{\ensuremath{\gamma}}$ equal to the energy gradient, which is estimated from geometric arguments. We use the drag ${F}_{d}$ from an outer flow to probe the trapping mechanism. When ${F}_{d}l{F}_{\ensuremath{\gamma}}$, the drop deforms but remains anchored to the hole. Its shape provides information about the pressure field. At higher flow velocities, the drop detaches, defining a critical capillary number for which ${F}_{d}={F}_{\ensuremath{\gamma}}$. The measured anchoring force agrees with the geometric model. |
