Internal structure of random polydisperse foams in steady state

The interplay between the foam structure and the liquid fraction, which has been established theoretically, is difficult to access experimentally due to foam aging. Here, we use small-angle neutron scattering coupled with optical imaging to investigate the structure of foams under stationary conditions where the liquid fraction remains constant over time. Through forced drainage, i.e., by injecting the foaming solution at a low flow rate above the foams, the coalescence and coarsening of polyhedral bubbles are suppressed. At the nanoscale, the thin film thickness and specific surface area of the films and Plateau borders swell and reach constant values during forced drainage. Although foam is by nature a non-equilibrium system, the low drainage flow rates considered place the structure in a steady state. Under these conditions, theoretical models based on Kelvin cells for monodisperse foams enable to predict the structure of our foams, despite being polydisperse, as long as they are in a steady state obtained in forced drainage.