Surfactant spreading on a thin viscous film supported by a stretchable wall is
examined computationally and analytically to study the effects of breathing
on surfactant replacement therapy (SRT). We investigate the influence of
oscillatory stretch of the finite wall on the spreading of surfactant in
the presence of a pre-existing surfactant. The model is developed using
lubrication theory, conservation of surfactant and fluid mass, and isotherms
for insoluble and soluble surfactants. Numerical solution shows there is
an optimal frequency for fastest surfactant spreading for both soluble and
insoluble surfactant, suggesting that an optimal breathing frequency for SRT
may exist. In addition to the initial transient spreading phase described above,
the mean-steady transport that is responsible for most of the transport in SRT. By
reversing the concentration gradient, we investigate surfactant and liquid clearance from
Bench top experiments using a stretchable membrane subjected to
oscillatory stretch with an essentially insoluble surfactant confirm the
numeric results for the insoluble case.
This work supported by NIH grant HL-41126 and NSF grant CTS-9412523.
Transient surfactant spreading with wall stretch. (7.48 MB)
This movie shows a numerical simulation of surfactant spreading on a thin film that is
supported by a stretching membrane. The film is initially clean, except for the new surfactant region.
The new surfactant begins spreading when the wall stretch starts. A fluid mechanical shock forms near the leading
edge of the new surfactant front. The shock is quite steep and the wave appears to break when it reaches the wall of the membrane.