[Webinar] Liquid Foams: From Basic Principles over Practical Aspects to Future Perspectives
Part 1: What is the difference between foamability and foam stability? How do liquid fraction, foam volume, and bubble size evolve as a function of time for stable and unstable foams, respectively? How can I study foams reproducibly? Under which circumstances can I compare the properties of foams generated with different surfactants? The first part of this presentation will answer these questions!
Part 2: 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. Thus we studied the influence of surfactant depletion on foam properties. We measured the surfactant loss of the bulk solution via surface tension measurements and then compared our data with the results of purely geometric considerations. 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 .
Part 3: Do intermolecular H-bonds between surfactant head groups play a role for foam stability? To answer this question we looked at the foam stability of various surfactants with C12 alkyl chains but different head groups and we found that stable foams are only generated when hydrogen bonds can form between the head groups [2,3]. Formation of hydrogen bonds between surfactant head groups – i.e. of a “hydrogen belt” at the interface – gives rise to a short-range attractive interaction that may render the surfactant layer more rigid (in the sense that the mobility of the molecules is restricted) and more elastic (in the sense that deformations can be counteracted). We expect an enormous impact on the future design of surfactants which must take intersurfactant H-bonds into account!
 On how Surfactant Depletion during Foam Generation Influences Foam Properties, J. Boos, W. Drenckhan, C. Stubenrauch, Langmuir, 2012, 28, 9303-9310
 On How Hydrogen Bonds Affect Foam Stability (Review), C. Stubenrauch, M. Hamann, N. Preisig, V. Chauhan, R. Bordes, Adv. Colloid Interf. Sci., 2017, 247, 435-443
 Intersurfactant H-bonds between Head Groups of n-Dodecyl-D-Maltoside at the Air-Water Interface, M. Kanduč, E. Schneck, C. Stubenrauch, JCIS, 2021, 586, 588-595