Black dots as a detector of self-assembly in thin liquid films

Experiments with different types of amphiphilic substances exhibit two stable tendencies. (1) The surface tension/concentration curves (Δσ/Cs) display well-defined kink and plateau sectors. (2) Free thin liquid films (foam films) from solutions with concentrations in the plateau regions drain until ‘black dots’ appear and then rupture almost immediately. A general theoretical scheme is developed that suggests a mechanism connecting the formation of black dots with the onset and the reorganization of smaller self-assembled aggregates (premicelles) in the bulk of the solution and on the interfaces. The results show that the black dots in free thin liquid films may serve as an indicator of the presence and reorganization of self-assembled structures in amphiphilic solutions.