Surfactant transport between foam films

Surfactant transport from foam film to foam film is an essential (yet poorly understood) aspect of the viscoplastic yielding behaviour of flowing foam. Recent experimental and modelling work by Bussonnière & Cantat (J. Fluid Mech., vol. 922, 2021, A25) has, however, helped to advance understanding of the relevant surfactant transport processes: the significance of that work is described herein.

Increasing the stability of the fire extinguishing foam by replenishing the liquid phase during sprinkling

Introduction. The destruction of foam films occurs when they reach critical thickness and lose the liquid phase as a result of syneresis and evaporation, which are rather difficult to slow down. We have proposed a method for increasing the stability of the fire extinguishing foam by means of replenishing the liquid phase through sprinkling.Methods. Foam stability was measured by the time of destruction of 25 % of the initial foam volume. The concentration of the foaming agent in the sprinkled solution varied from 0.5 to 6 %. Carboxymethylcellulose sodium salt (Na CMC) was used as a stabilizing additive. Field studies were carried out by feeding foam and solution from two AT-3,2-40 (43253)001-MS tank cars.Results and discussion. It has been established that the foam stability is influenced by the sprinkling intensity and the foaming agent concentration. Foam sprinkling with the solutions having low concentration of thefoaming agent leads to the washout of surfactants from the films that reduces the foam stability. The sprinkling intensity reduction boosts the foam stability due to the replenishment of the moisture lost through evaporation. The foam stability was maximal in case of sprinkling with a 2 % solution of the foaming agent, while the sprinkling intensity had no influence. An increase in the concentration of the foaming agent in the sprinkled solution led to a decrease in the foam stability. It is found that a smaller amount of the foaming agent is consumed to maintain the amount of foam through sprinkling than to replenish the destroyed amount through additional foam generation. It is shown that various stabilizing additives can be added to the foam in the process of sprinkling. If Na CMC is added to the solution exposed to sprinkling, the time of foam destruction goes up 3–5 times even in case of a non-recurrent sprinkling session. Field tests have confirmed the feasibility of adding stabilizing additives to the foam by means of sprinkling.Conclusions. The results of the research have shown the feasibility of co-feeding the foam and surfactant solutions, containing various stabilizing additives, in order to extinguish fires and generate stable foams.

Foam film stratification studies probe intermicellar interactions

Ultrathin foam films containing supramolecular structures like micelles in bulk and adsorbed surfactant at the liquid–air interface undergo drainage via stratification. At a fixed surfactant concentration, the stepwise decrease in the average film thickness of a stratifying micellar film yields a characteristic step size that also describes the quantized thickness difference between coexisting thick–thin flat regions. Even though many published studies claim that step size equals intermicellar distance obtained using scattering from bulk solutions, we found no reports of a direct comparison between the two length scales. It is well established that step size is inversely proportional to the cubic root of surfactant concentration but cannot be estimated by adding micelle size to Debye length, as the latter is inversely proportional to the square root of surfactant concentration. In this contribution, we contrast the step size obtained from analysis of nanoscopic thickness variations and transitions in stratifying foam films using Interferometry Digital Imaging Optical Microscopy (IDIOM) protocols, that we developed, with the intermicellar distance obtained using small-angle X-ray scattering. We find that stratification driven by the confinement-induced layering of micelles within the liquid–air interfaces of a foam film provides a sensitive probe of non-DLVO (Derjaguin–Landau–Verwey–Overbeek) supramolecular oscillatory structural forces and micellar interactions.

Chlamydomonas reinhardtii swimming in the Plateau borders of 2D foams

Living phototactic algae cells swim in foam films with adjusted speeds controlled by the fluidic channel width.

Drainage via stratification and nanoscopic thickness transitions of aqueous sodium naphthenate foam films

Sodium Naphthenates (NaNs), found in crude oils and oil sands process-affected water (OSPW), can act as surfactants and stabilize undesirable foams and emulsions. Despite the critical impact of soap-like NaNs...

Surface Forces and Stratification in Foam Films Formed with Bile Salts

Bile salts, especially in their aggregated or micellar form, play a critical role in health and medicine by solubilizing cholesterol, fat-soluble vitamins, and drugs. However, in contrast to the head-tail...

Flow Effects on the Surface Properties of Surfactant Foam Films

The surface electrostatic properties of the liquid foam, involving the electrokinetic (EK) phenomena in the liquid-gas interface, have significant effects on the stability of foam. Here, we established a theoretical...