Duality of Foam Stabilization

Abstract Can a foam reversibly switch between particle and surfactant stabilization? Sure it can. Foams are usually stabilized either by surfactant or hydrophobic nanoparticles. Their combination often worsens the stability of the foam, with surfactant adsorption on the particles causing complex behavior. A system that shifts between both types of mechanisms is desirable both for fundamental studies and practical applications. We developed a system consisting of aqueous solution of 0.1 mM sodium dodecyl sulfate (SDS) + 1.23 mM ZnSO4 + 1.23 mM ethylenediaminetetraacetic acid (EDTA). The foam was produced by the shaking method. The pH value was varied by small additions of HCl or NaOH. We tuned the foam lifetime from 15 – 20 seconds (at pH = 3 – 6), to ~ 180 seconds near pH=1, and increase it in the pH range of 6 to 12, reaching 15 minutes at pH=12. This is due to emerging of nanoparticles of Zn(OH)2 at pH>8, smoothly switching between the stabilization mechanisms. The nano-suspension of Zn(OH)2 is transparent due to the low aggregation. The low cost (