Foam films from oppositely charged polyelectolyte/surfactant mixtures: Effect of polyelectrolyte and surfactant hydrophobicity on film stability

The present study focuses on the stability control of foam films from oppositely charged polyelectrolyte/surfactant mixtures, namely, on the cationic surfactant dodecyl trimethyl ammonium bromide (C(12)TAB) mixed with highly negatively charged polyelectrolytes. The net charge of the system can be tuned by varying the polyelectrolyte concentration so that the film behavior around the isoelectric point (IEP) can be studied. The measurements of the disjoining pressure isotherms show that the polyelectrolyte/surfactant ratio has an important influence on film stability, with a stability minimum close to the IEP and very stable films above that point. However, in the concentration regime in which the most stable films are formed, the surface coverage is very low, implying that the net charge in the system dominates the film stability and not the complexes at the surface. Comparison with a previous work showed that the choice of surfactant plays an important role for tuning the foam stability while the type of polyelectrolyte has only a minor impact.