Leonardo Chiappisia , Julien Lamolinairie a,b, Jean-Luc Bridotc, Pierre Bauduinb, and Olivier Diatb
a Institut Max von Laue – Paul Langevin, 71 avenue des Martyrs, 38042, Grenoble, France
b ICSM, CEA, CNRS, ENSCM, Univ. Montpellier, 30207 Bagnols-sur-Cèze, France
c Teclis Scientific, 69380, Civrieux-d’Azergues, France
Lamolinairie, J.; Bridot, J.-L.; Bauduin, P.; Chiappisi, L.; Diat, O. Foams Stabilized by Superchaotropic Ions: The Birth, Life, and Collapse of Unconventional Systems. J. Colloid Interface Sci. 2026, 724, 141150. https://doi.org/10.1016/j.jcis.2026.141150.
Liquid foam, a dispersion of air in a liquid is a complex fluid that is intrinsically out-of-equilibrium. All foam properties are governed by the interplay of structural elements spanning several orders of magnitude, from macroscopic air bubbles and connected liquid channels hundreds of micrometres thick, to inter-bubble films only tens of nanometres thick, and nanometre-sized colloids. Characterising these features simultaneously during foam formation and throughout liquid drainage is therefore essential for understanding its evolution and stability.
Through a collaboration between the ILL, ICSM and Teclis Instruments, the authors developed a multiscale approach combining SANS, conductivity and optical imaging to achieve such a comprehensive characterisation of liquid foams. This work was published in Soft Matter in 2022 [1]. A representative selection of results obtained using this setup is shown in Figure 1.
Neutron scattering is particularly well suited to probing the nanoscale structure of liquid foams, which are opaque to visible light. Moreover, its large beam probes a representative volume of the foam, simultaneously sampling hundreds of films.
This approach enables the correlation of nanoscale inter-bubble film and Plateau border thicknesses with changes in the macroscopic foam structure. In particular, it enables the complementary characterisation of specific surface area, liquid fraction, film thickness and bubble size, providing an experimental framework for quantitatively linking the different structural scales of a foam and estimating the various intrinsic pressure components that oppose liquid drainge.
In their more recent work, published in the Journal of Colloid and Interface Science [2], the authors investigated the role of interfacial chemistry in stabilizing non-ionic foams through the introduction of charge, either by adding an ionic surfactant or nanometer-sized superchaotropic ions. The latter stabilize foams as effectively as conventional ionic surfactants, significantly extending their lifetime.
Interestingly, the relationship between foam film thickness and disjoining pressure suggests that film equilibrium in real foams depends not only on hydrostatic pressure and the initial formulation, but also on local composition, the distribution of ions and surfactants, and osmotic pressure gradients between films and Plateau borders. This picture is complemented by concurrent work by L. Chiappisi, published in Physical Review E in 2026 [3], which highlights the role of micelle redistribution within the foam. The study reveals a substantial increase in micelle concentration in Plateau borders as foam height and age increase.
These studies [1-3] advance the fundamental understanding of liquid foam physics, particularly by bridging the behaviour of films in 3D foams and isolated thin films, while also opening promising prospects for applications in ionic extraction, separation and fractionation , an area currently investigated at the ICSM [4].
References
[1] J. Lamolinairie, B. Dollet, J.L. Bridot, P. Bauduin, O. Diat, L. Chiappisi, Probing foams from the nanometer to the millimeter scale by coupling small-angle neutron scattering, imaging, and electrical conductivity measurements, Soft Matter 18(46) (2022) 8733–8747.
[2] J. Lamolinairie, J.L. Bridot, P. Bauduin, L. Chiappisi, O. Diat, Foams stabilized by superchaotropic ions: The birth, life, and collapse of unconventional systems, J Colloid Interf Sci 724 (2026).
[3] L. Chiappisi, Micelle enrichment in liquid foams, Phys Rev E 113(6) (2026).
[4] K. Skorzewska, A. Jonchère, C. Pasquier, L. Girard, P. Bauduin, Superchaotropic ion flotation: A new concept for the extraction and separation of nanometer-sized ions by non-ionic surfactant-based foams, Sep Purif Technol 323 (2023).
Figure: Representative selection of experimental data and time-resolved results (bubble radius, specific surface, plateau border radius, foam film thickness) obtained for a surfactant-stabilised foam under free-drainage conditions. The combination of optical imaging and small-angle scattering provides these complementary information on the different structural elements of the liquid foam.
