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2001 - 2005

Foam films stabilized by poly(ethylene imine)
Citation key klit02b
Author von Klitzing, R. and Kolaric, B.
Pages 247-253
Year 2002
Journal Tenside Surf. Det.
Volume 39
Number 6
Abstract This paper describes disjoining pressure measurements on freestanding films produced from aqueous solutions containing cationic surfactant and the polybase poly(ethylene imine) (PEI). The disjoining pressure isotherms show steps in film thickness due to oscillating disjoining pressure. in the case of branched polyelectrolytes, the relationship between the size of the film thickness step Deltah and the PEI concentration c is Deltah proportional to c(-1/3). This leads to the conclusion that the PEI molecules are ordered in layers within the film, and that they are pressed out layer by layer. With decreasing polymer charge density (adjusted by pH and the degree of polymer branching), the pressure which has to be applied to induce a step in film thickness is reduced and the drainage velocity decreases. This means that the ordering of the polyelectrolytes within the film is induced by the electrostatic repulsion between the polyelectrolytes. The step size is related to the diameter of the polymer and the thickness of the surrounding cloud of free counterions. From the results at different polymer concentrations, it is concluded that most of the counterions are entrapped within the PEI molecules and that only 10% of the counterions are free.
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