Stabilization of foams by the combined effects of an insoluble gas species and gelation

Abstract

Liquid foams are unstable due to aging processes such as drainage, coalescence or coarsening. Since these processes modify the foam structure, they can be a severe limitation to the elaboration of solid foams with controlled structures inherited from their liquid precursors. Such applications call for a thorough understanding of foam stabilization. Here we study how coarsening can be inhibited by the combined effects of a mixture of gas containing a species insoluble in the foaming solution and of gelation of the foaming solution. We present experiments with model ordered liquid foams and hydrogel foams. They allow us to identify the underlying physical mechanisms of stabilization and their governing parameters, namely the bubble radius R, the foam shear modulus G and the number η of insoluble trapped gas molecules per bubble. We propose a scaling model that predicts the stability diagram of an ideal monodisperse perfectly ordered foam as a function of R, G and η, in qualitative agreement with our data. We show that the domain of stable foams is governed by a characteristic elasto-capillary radius set by the ratio of surface tension to storage modulus.

Surfactant Crystals as Stimulable Foam Stabilizers: Tuning Stability with Counterions

“…Colloidal particles and certain proteins are extremely efficient in creating mechanically resistant surface layers to stop coalescence and coarsening all together (Gonzenbach et al, 2006;Salonen et al, 2016;Stocco et al, 2011;Tcholakova et al, 2008Tcholakova et al, , 2017. Particles can also gel or get stuck in the foam structure to block drainage (Bey et al, 2017;Guillermic et al, 2009;Haffner et al, 2014;Khidas et al, 2014;Louvet et al, 2010).…”

Monodisperse Highly Ordered and Polydisperse Biobased Solid Foams

“…gas diffusion within the foam, results in a change of the bubble size distribution but the overall foam volume is not affected. To confirm this assumption that gas diffusion to the atmosphere is responsible for damaging the foam's top layer, we studied the evolution with time of monodisperse chitosan monolayers in the presence of cross-linker (Figure 3.9), in order to find out if gelation can stop gas diffusion and/or Ostwald ripening [Dut04,Bey17].…”

Stability criterion for fresh cement foams

“…Besides, several samples are prepared by following a different procedure in order to stop one or two destabilization mechanisms. To prevent ripening, we use perfluorohexane saturated nitrogen instead of pure nitrogen [1,7]. Chemical formula of perfluorohexane is C 6 F 14 and it has a very low solubility in water, which reduces the global gas transfer rate between the bubbles.…”