Impact of Fluorocarbon Gaseous Environments on the Permeability of Foam Films to Air

Abstract

A mobile soap film, stabilized with tetradecyltrimethylammonium bromide (TTAB) or sodium dodecylsulfate (SDS) surfactants and deposited in the middle of a cylindrical tube separates the tube into two distinct gaseous compartments. The first compartment is filled with air while the second one contains a mixture of air and perfluorohexane (C 6 F 14 ), which is a fluorinated gas barely soluble in water. This soap film thus acts as a liquid semi-permeable membrane for gases equivalent to solid semipermeable membranes conventionally used in fluid separation processes. To infer the rate of air transfer through the membrane, we measure the displacement of the mobile soap film. From this, we deduce the instantaneous permeability of the membrane. In contrast to the permeability of solid membranes, which inexorably decreases over time because they become clogged, an anti-clogging effect is observed with a permeability that systematically increases over time. Since the thickness of the film is constant over time, we attribute this to the possibility of adsorbing or desorbing fluorinated gas molecules on the liquid membrane. Indeed, the partial pressure of the fluorinated gas being high at the beginning of the experiment, the density of the adsorbed molecules is also high, which leads to a low permeability to air transfer. On the contrary, at the end of the experiment, the partial pressure in fluorinated gas and thus the density of the adsorbed molecules are low. This leads to a higher permeability and a less clogged membrane.

Fluorocarbon Vapors Slow Down Coalescence in Foams

“…We hypothesize that this is due to the formation of a mixed fluorocarbon/surfactant layer at the gas/water interface. The complex properties of surfactant monolayers in the presence of fluorocarbons have been investigated in depth in recent years, [10][11][12][13][14][15] yet without establishing a link to foam properties. Our findings open new possibilities of controlling foam stability by introducing a "coadsorbate" from the gas phase.…”

Leaching Foams for Copper and Silver Dissolution: A Proof of Concept of a More Environmentally Friendly Process for the Recovery of Critical Metals

“…When N2 is used to make the foam, N2 is bubbled in the solution during 30 minutes to remove dissolved dioxygen. During foaming, air and nitrogen are bubbled into perfluorohexane (C6F14-CAS 355-42-0 as traces of this water-insoluble gas in the bubbles enable to slow down Oswald ripening and increase the foam stability (24)(25). The experiment consists in stirring either a copper plate, (2 𝑐𝑚 × 2 𝑐𝑚 × 675 µ𝑚, purchased at Alfa Aesar, purity 99.9%) or a silver plate (2 cm x 2cm x 250 µm, purity 99.9%, purchased at Sigma-Aldrich) at 40 rpm for five hours (using a RZR 2020 stirrer from Heidolph), in a 3 neck round bottom flask filled with 100 mL of foam or solution.…”

“…When N 2 is used to make the foam, N 2 is bubbled in the solution during 30 min to remove dissolved dioxygen. During foaming, air and nitrogen are bubbled into perfluorohexane (C 6 F 14 – , CAS 355-42-0) as traces of this water-insoluble gas in the bubbles slow down Oswald ripening and increase the foam stability. , The experiment consists in stirring either a copper plate (purchased at Alfa Aesar, purity 99.9%) or a silver plate (2 cm × 2 cm × 250 μm, purity 99.9%, purchased at Sigma-Aldrich) at 40 rpm for 5 h (using a RZR 2020 stirrer from Heidolph), in a three neck round-bottom flask filled with 100 mL of foam or solution. For foam experiments (Figure b), 15 mL of the surfactant solution containing HCl or H 2 SO 4 are poured into the flask and the gas is then injected through a porous fritted glass (pore diameter: 16–40 μm, supplied by ROBU Glasfilter Geräte GmbH) at a flow-rate of 60 mL/min for about 2 min to reach a total foam volume of 100 mL; therefore, the liquid fraction of the foams is of the order of 15%.…”

Transport of Heptane Molecules across Water–Vapor Interfaces Laden with Surfactants

“…For example, the adsorption of fluorocarbon molecules on hydrocarbonsurfactant monolayers has been shown to suppress the transport of air molecules through them. 7 Furthermore, liquid films often separate surfactant monolayers (e.g., in foams), and their thickness can affect the gas transport through those monolayers. For example, the permeability of insoluble gases such as N 2 through hydrocarbon-surfactant monolayers decreases as the water film separating them becomes thin, thereby suggesting that the resistance of those surfactant monolayers to N 2 transport increases with decreasing water film thickness.…”