Ion-specific effects on foam films and foam from diluted solution of sodium dodecyl sulfate

Abstract

The ion-specific effects on extremely diluted solutions of surfactants are poorly studied. The effect of Li+ , Na+ and K+ ions on the properties of foam films and foam stabilized by 0.05 mmol/L sodium dodecyl sulfate (SDS) was studied. Each one of the salts LiCl, NaCl and KCl in the concentration range of 1.1 mmol/L to 50 mmol/L was added to 0.05 mmol/L solution of SDS, for studying the properties of its foam films and foams. It was established that the surface potential of the foam films does not depend on the type of salt added, which means that no ion-specific effects are registered. On the contrary, such effects are evident in the case of foam produced by sparging of gas through porous bottom of column containing the same solutions. Thus, the rates of foaming, foam decay and the foam lifetime vs. the concentration of added salt (LiCl, NaCl and KCl) were studied by means of Dynamic Foam Analyzer (DFA-100, Kruss Ltd, Germany). The foam production number for each one of these cases was calculated as well. It was established that both NaCl and KCl boost the foam, the first one of which being stronger than the second one. On the contrary, LiCl has no effect on the foamability of the system. The present study is an example for manifestation of a salt-specific effect under dynamic conditions, which vanishes under static conditions.