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

Experiments with different types of amphiphilic substances exhibit two stab le tendencies. (1) The surface tension/concentration curves (Delta sigma ;C -s) display well-defined kink and plateau sectors. (2) Free thin liquid fil ms (foam films) from solutions with concentrations in the plateau regions d rain until 'black dots' appear and then rupture almost immediately. A gener al theoretical scheme is developed that suggests a mechanism connecting the formation of black dots with the onset and the reorganization of smaller s elf-assembled aggregates (premicelles) in the bulk of the solution and on t he interfaces. The results show that the black dots: in Free thin liquid fi lms may serve as an indicator of the presence and reorganization of self-as sembled structures in amphiphilic solutions. (C) 2001 Elsevier Science B.V. All rights reserved.