Direct Observation of Langmuir Monolayer Flow through a Channel

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Abstract
Fluorescence microscopy was used to observe the velocity profile in a Langmuir monolayer forced through a channel. The monolayer was studied in the liquid-expanded-liquid-condensed coexistence region; the flow profile was invariant as the area fraction of the condensed phase was varied from 0.07 to 0.7. The hydrodynamic problem of a semi-infinite viscous fluid driven by a surface tension gradient through a channel was solved exactly; a semielliptical velocity profile is obtained, in precise agreement with the experiments, thereby demonstrating that the flow is controlled by coupling to the subphase.