DIRECT OBSERVATION OF LANGMUIR MONOLAYER FLOW-THROUGH A CHANNEL

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 v iscous fluid driven by a surface tension gradient through a channel wa s solved exactly; a semielliptical velocity profile is obtained, in pr ecise agreement with the experiments, thereby demonstrating that the f low is controlled by coupling to the subphase.