Here, we will focus on modelling a new type of artificial microswimmers where propulsion is achieved by Marangoni flow
This simple example of Marangoni flow
is highly relevant to coatings because quite often, surface tension driven flows or surface tension differential driven flows develop in coatings as they dry and this can lead to highly detrimental imperfections in the applied coating.
Sufactant adsorbtion and Marangoni flow
in liquid jets.
This is understood by inspection of Figure 18, which shows that a phase-shift occurs between the film thickness and the surfactant surface concentration that results in a situation wherein the concentration is larger downstream of the wave peak than upstream; this drives the retarding Marangoni flow.
Surfactants lower the liquid surface tension, which promotes wave formation but they also give rise to surface tension gradient-driven or Marangoni flow.
The degree of BLRO depends on competing flows--surface-tension-gradient Marangoni flow increases BLRO while pressure-gradient flow decreases BLRO.
In Marangoni flow the time rate of change in film thickness depends on the film thickness squared
Hence, leveling dominates over Marangoni flow for thick films.
Since the velocity of Marangoni flow is inversely proportional to viscosity (Eq 10).