ASYMMETRIC DRAINAGE IN FOAM FILMS

The same basic mechanism is responsible for asymmetric drainage of thi n circular films and marginal regeneration in vertical, rectangular fi lms. A linear stability analysis showed that these phenomena are cause d by a hydrodynamic instability that is produced by a surface-tension- driven flow and stabilized by surface viscosity, surface diffusivity, and the system length scale. A criterion for the onset of this instabi lity was derived. Experiments performed on small circular films of aqu eous solutions of SDS and SDS-1-dodecanol demonstrated the strong stab ilizing effect of surface viscosity. Experimental results were found t o be in good agreement with the predictions of the linear stability an alysis.