Even though foams have been the subject of intensive investigations over the last decades, many important questions related to their properties remain open. This concerns in particular foams which are stabilized by mixtures of surfactants. The present study deals with the fundamental question: which are the important parameters one needs to consider if one wants to characterize foams properly? We give an answer to this question by providing a measuring protocol which we apply to well‐known surfactant systems. The surfactants of choice are the two non‐ionic surfactants n‐dodecyl‐β‐d‐maltoside (β‐C12G2) and hexaethyleneglycol monododecyl ether (C12E6) as well as their 1:1 mixture. Following the suggested protocol, we generated data which allow discussion of the influence of the surfactant structure and of the composition on the time evolution of the foam volume, the liquid fraction, the bubble size and the bubble size distribution. This paper shows that different foam properties can be assigned to different surfactant structures, which is the crucial point if one wants to tailor‐make surfactants for specific applications.

Although it is known that foaming a surfactant solution results in a depletion of the surfactant in the bulk phase, this effect is often overlooked and has never been quantified. Therefore, the influence of surfactant depletion on foam properties using solutions of the two nonionic surfactants, n-dodecyl-β-D-maltoside (β-C(12)G(2)) and hexaethyleneglycol monododecyl ether (C(12)E(6)), were investigated. These investigations were conducted in two steps. First, different foam volumes were generated with the same surfactant solution at a concentration of c = 2 cmc. It was found that the higher the foam volume, the larger the surfactant depletion. Second, two different bulk concentrations (c = 2 and 1.33 cmc) were used for the generation of 50 and 110 mL of foam, respectively. For a foam volume of 50 mL, no differences were observed, whereas generating 110 mL led to different results. The surfactant loss in the bulk solution was measured via surface tension measurements and then compared to the results of purely geometric considerations that take into account the amount of interface created in the foam. Both results were in very good agreement, which means that surfactant depletion can be calculated in the way suggested here. Under conditions where depletion plays a role, our approach can also be used to estimate the bubble size of a foam of known volume by measuring the surfactant concentration in the bulk solution after foaming.

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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.