Comparison between generations of foams and single vertical films – single and mixed surfactant systems

Abstract

The purpose of this article is to compare experiments carried out with single vertical foam films and with foams. We focus on the generation of films and foams and measure (i) the quantity of water entrained and (ii) the stability of the systems. The surfactants we used are C12E6, β-C12G2 and their 1 : 1 mixture because those systems are very well characterised in the literature and are known to stabilise foams with very different properties. We show that the quantity of water uptake in foams and single vertical films scales in the same way with the velocity of generation. However, the different surfactant solutions have different foamabilities, whereas the films they stabilise have exactly the same thickness. Moreover, the foamability of a C12E6 solution is much lower than that of a β-C12G2 solution or of a solution of the 1 : 1 mixture. This is due to the rapid rupture of the C12E6 foam films during foam generation. Surprisingly, the isolated films have exactly the same lifetime for all the surfactant solutions. We conclude that, though drawing a correlation between films and foams is tempting, the results obtained do not allow correlating of film and foam stability during the generation process. The only difference we observed between the single films stabilised by the different solutions is the stability of their respective black films. We thus suggest that the stability of black films during foam generation plays an important role which should be explored further in future work.

Enhanced Foamability of Sodium Dodecyl Sulfate Surfactant Mixed with Superspreader Trisiloxane-(poly)ethoxylate

“…Gravitational drainage technique was introduced for the first time to measure surface elasticity of the ordinary surfactants (ionic and nonionic surfactants, which form micelles) and the disjoining pressure of superspreaders (nonionic surfactants, which form bilayers) in plane films using microinterferometric technique. In the subsequent work this technique was adopted to study film stabilization by some other ordinary surfactants, and a correlation between the foam stability and foamability of surfactant solutions. However, no correlation was established between thin film stability and foamability for the system studied …”

“…In the subsequent work this technique was adopted to study film stabilization by some other ordinary surfactants, and a correlation between the foam stability and foamability of surfactant solutions. However, no correlation was established between thin film stability and foamability for the system studied …”

Foamability of aqueous solutions: Role of surfactant type and concentration

“…In the various studies of foaming several physicochemical parameters were proposed to explain the variations in the foamability of the surfactants solutions: surfactant concentration [11] and its relation to the critical micellar concentration (CMC); dynamic surface tension (DST) [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]; surface mobility expressed through the Marangoni effect [28], surface modulus [29] or surface elasticity [30] of the adsorption layers; stability of the single foam films [31,32] expressed through the disjoining pressure [33] and its components, such as steric repulsion and structural forces [33][34][35]. Generally speaking, each of these characteristics could be important and their interplay should be understood much better if we want to describe and control the complex process of foam formation.…”

“…Marangoni effect is related to the surface Gibbs elasticity, E G , which acts to restore the homogeneous distribution of surfactant along the film surface. In [32] the properties of single vertical foam films and the foamability of solutions containing different surfactants were compared. The results showed that only the stability of black films under dynamic conditions has some correlation with the foamability of the same surfactant solutions for different surfactant types.…”

“…surface modulus [29] or surface elasticity [30] of the adsorption layers; stability of the single foam films [31,32] expressed through the disjoining pressure [33] and its components, such as steric repulsion and structural forces [33][34][35]. Generally speaking, each of these characteristics could be important and their interplay should be understood much better if we want to describe and control the complex process of foam formation.…”