Disjoining Pressures and Film Stability of Alkyltrimethylammonium Bromide Foam Films

Abstract

The alkytrimethylammonium bromide surfactant series, CnTAB, n ) 10, 12, 14, 16, is used to perform a systematic study of the forces and stability of foam films produced from soluble cationic surfactants. Both surface tension and disjoining pressure isotherms are measured for each surfactant. This information is then combined with neutron reflectivity and dynamic surface tension results found in the literature to provide an understanding of how the surfactant chain length can effect the forces and stability in thinliquid films. For stable films, we find good quantitative agreement between the interaction forces measured in foam films and those reported from surface force studies on similar systems. We also find that the surfactant's hydrocarbon chain length and packing can strongly influence film stability. For highly purified surfactants an abrupt increase in film stability is seen when extending the chain length from C 12TAB to C14TAB. When an uncharged cosurfactant is present, this stability transition takes place between C10TAB and C12TAB. Both transitions correlate well with changes in the monolayer's cohesive strength, and we outline how monolayer cohesion can play a stabilizing role by dampening both spatial and density fluctuations at the air-water interface.

Foamability of sodium dodecyl sulfate solutions: Anomalous effect of dodecanol unexplained by conventional theories

“…High values of surface viscoelasticity can potentially lead to the suppression of marginal regeneration and a reduced rate of foam film drainage [24][25][26] and coalescence [3,12] therefore, a good correlation between the liquid film or foam stability and the surface viscoelasticity has been found [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42]. If the enhanced viscoelasticity is developed on airwater interface during foam generation (at surface ages < 1s), foamability can also be enhanced.…”

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

“…[1][2][3] In some processes like fire fighting a foam is desired, while in others (e.g. in washing machines) foaming should be avoided, which shows the high importance of foam stability control.…”

“…28,29 C 14 TAB was chosen as surfactant, as it is the shortest surfactant in the C n TAB series that forms stable films on its own. 1 This makes it possible to investigate the whole concentration regime from films of pure surfactant solutions, over those which contain little polyelectrolyte to films with a high polyelectrolyte concentration. The latter can already show stratification behavior.…”

“…When the exchange between the surface and the bulk phase is slow, this results in a high surface elasticity, which in turn results in higher foam stability. 1,40 It is surprising that the surface elasticity for the sPSO 2 -220/ C 14 TAB mixtures is lower than for PAMPS/C 14 TAB and PSS/C 14 TAB Fig. 5 The maximum disjoining pressure P max before film rupture versus respective polyelectrolyte concentration for sPSO 2 mixtures at low polyelectrolyte concentrations.…”

“…Additionally, at concentrations beyond the BSMP, the higher surface elasticity of sPSO 2 -220/C 14 TAB mixtures helps to explain the significantly higher foam film stability of sPSO 2 -220/C 14 TAB in comparison to PAMPS/C 14 TAB mixtures, since high surface elasticities are known to increase foam film stability. 1,40 The Debye length k À1 of sPSO 2 -220/C 14 TAB mixtures was extracted. With increasing sPSO 2 -220 concentration the Debye length k À1 decreases as the ionic strength increases.…”