Effect of polyelectrolytes on (de)stability of liquid foam films

Abstract

The review addresses the influence of polyelectrolytes on the stabilisation of free-standing liquid foam films, which affects the stability of a whole macroscopic foam. Both the composition of the film surface and the stratification of the film bulk drives the drainage and the interfacial forces within a foam film.Beside synthetic polyelectrolytes also natural polyelectrolytes like cellulose, proteins and DNA are considered.

Surface adsorption of sulfonated poly(phenylene sulfone)/C14TAB mixtures and its correlation with foam film stability

“…The synergistic lowering of the surface tension by sPSO 2 -220/C 14 TAB mixtures can be explained by the formation of surface active polyelectrolyte/surfactant complexes. 5,13,14 The formation of polyelectrolyte/surfactant complexes is energetically favorable due to the decrease in electrostatic repulsion (between positively charged surfactant headgroups at the surface) and the increase in entropy due to the release of counterions. 43,44 Another explanation for the synergistic lowering of the surface tension would be a synergistic co-adsorption of polyelectrolyte and surfactant molecules.…”

“…6,7 Depending on the charge combination of the used polyelectrolytes and surfactants, either a Common Black Film (CBF) with a thickness of 10-100 nm, or a Newton Black Film (NBF) with a thickness below 10 nm is formed as the final state before film rupture. 5,8 CBFs are electrostatically stabilized due to the presence of surface charges, while NBFs are stabilized by steric repulsions of the adsorbed complexes. CBFs contain two surface layers with differing amounts of water between them, while NBFs consist of only two layers of adsorbed molecules and their respective hydration shells.…”

“…When mixing the two compounds, highly surfaceactive complexes can form due to electrostatic interactions. 4,5 Polyelectrolyte/surfactant mixtures play an important role in cleaning products and cosmetics. 6,7 Depending on the charge combination of the used polyelectrolytes and surfactants, either a Common Black Film (CBF) with a thickness of 10-100 nm, or a Newton Black Film (NBF) with a thickness below 10 nm is formed as the final state before film rupture.…”

“…Firstly, the dissociation degree of C 14 TAB might be below 100% in both mixtures, which would shift the BSMP to lower polyelectrolyte concentrations. 5,13 Secondly, the polyelectrolyte/surfactant mixing ratio at the surface might be different from that in the bulk, leading to a shift of the BSMP. 5 Thirdly, the pure air/water interface is slightly negatively charged.…”

“…5,13 Secondly, the polyelectrolyte/surfactant mixing ratio at the surface might be different from that in the bulk, leading to a shift of the BSMP. 5 Thirdly, the pure air/water interface is slightly negatively charged. 16 Thus, a part of the positive charges of the surfactant is needed to compensate these charges.…”