Relaxation Marangoni

The mechanism of the equilibrium elasticity acts until it is possible to provide a surfactant re-partition between the exterior and interior of the film. In a NBF such a repartition is not possible and this mechanism of elasticity ceases to act. The elasticity properties of bilayer films, in which the hydrodynamic and adsorption processes are characterised with normal time of relaxation, are due to Marangoni effect in the insoluble adsorption layers. That is why stable foams with black films are very sensitive to different local disturbances (heating, vibration, etc.). 

By assuming that Ns = const, which takes place either for insoluble surfactants or for the case in which the characteristic time of external action is substantially less than the relaxation time of the adsorption layer, and by differentiating (7.2.5) with respect to S, we obtain the following estimate for the Marangoni modulus of elasticity ... 

The field of Marangoni instabilities shows a large variety of dissipative structures, including the principle of stationary structures, hierarchical structures with limited self-similarity, relaxation oscillations and regular behavior of travelling autowaves with chaotic turbulence-like behaviour. There is also the oscillatory regime with trains of waves with soliton-like behaviour of each wave. Anormal as well as normal dispersion of these waves have recently... 

Figure 5. Illustration of the Gihhs-Marangoni effect in a thin liquid film. Reaction of a liquid film to a surface disturbance, (a) Low surfactant concentration yields only low differential tension in film. The thin film is poorly stabilized, (b) Intermediate surfactant concentration yields a strong Gibbs-Marangoni effect which restores the film to its original thickness. The thin film is stabilized, (c) High surfactant concentration (> cmc) yields a differential tension which relaxes too quickly due to diffusion of surfactant. The thinner film is easily ruptured. (From Pugh [109]. Copyright 1996 Elsevier, Amsterdam.)...

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