Journal of Fluid Mechanics

Concentration measurements downstream of an insoluble monolayer front

a1 Department of Mechanical, Aerospace, and Nuclear Engineering Rensselaer Polytechnic Institute, Troy, NY 12180, USA


The surfactant concentration distribution on a planar uniform flow with a surface-piercing barrier was measured via the nonlinear optical technique of second-harmonic generation. The measurements were performed for an insoluble surfactant monolayer on the air/water interface. A theoretical model balancing surface elasticity and bulk shear at the interface was developed to predict the concentration profile for any insoluble monolayer. Measured equations of state, relating the surface tension to the surfactant concentration, were used in the model along with velocity data obtained using boundary-fitted digital particle image velocimetry. Theoretical concentration profiles were in agreement with experimental results. Additionally, global predictions from the model for four different insoluble surfactant systems also showed agreement with experimental measurements.

(Received April 9 2001)
(Revised June 11 2002)