From Individual Liquid Films to Macroscopic Foam Dynamics: A Comparison between Polymers and a Nonionic Surfactant

Abstract

Foams can resist destabilizaton in ways that appear similar on a macroscopic scale, but the microscopic origins of the stability and the loss thereof can be quite diverse. Here, we compare both the macroscopic drainage and ultimate collapse of aqueous foams stabilized by either a partially hydrolyzed poly(vinyl alcohol) (PVA) or a nonionic low-molecular-weight surfactant (BrijO10) with the dynamics of individual thin films at the microscale. From this comparison, we gain significant insight regarding the effect of both surface stresses and intermolecular forces on macroscopic foam stability. Distinct regimes in the lifetime of the foams were observed. Drainage at early stages is controlled by the different stress-boundary conditions at the surfaces of the bubbles between the polymer and the surfactant. The stress-carrying capacity of PVA-stabilized interfaces is a result of the mutual contribution of Marangoni stresses and surface shear viscosity. In contrast, surface shear inviscidity and much weaker Marangoni stresses were observed for the nonionic surfactant surfaces, resulting in faster drainage times, both at the level of the single film and the macroscopic foam. At longer times, the PVA foams present a regime of homogeneous coalescence where isolated coalescence events are observed. This regime, which is observed only for PVA foams, occurs when the capillary pressure reaches the maximum disjoining pressure. A final regime is then observed for both systems where a fast coalescence front propagates from the top to the bottom of the foams. The critical liquid fractions and capillary pressures at which this regime is obtained are similar for both PVA and BrijO10 foams, which most likely indicates that collapse is related to a universal mechanism that seems unrelated to the stabilizer interfacial dynamics.

Probing foams from the nanometer to the millimeter scale by coupling small-angle neutron scattering, imaging, and electrical conductivity measurements

“…As soon as the Kiessig fringes are observable, the foam film thickness decreases from about 55 nm down to 40 nm a value which remains constant over the last 30 minutes of the experiment. These values are in the range of what has been determined using a thin film pressure balance technique on a single film submitted to an external pressure before rupture, but still much thicker than Newton black films 69 . Finally, the last microscopic features are the specific areas from Plateau borders and foam films.…”

“…These values are in the range of what has been determined using a thin film pressure balance technique on a single film submitted to an external pressure before rupture, but still much thicker than Newton black films. 69 Finally, the last microscopic features are the specific areas from Plateau borders and foam films. Their sum agrees very well with the results from the image analysis, at least in the last 30 minutes, supporting the use of the absolute scale in the scattering experiment.…”

Foam aging under free drainage analysed using associated operando techniques

“…Determining roughly the Plateau borders radius from image analysis, of about rP B = 24 µm in this second temporal phase and with the measurement of the surface tension in this system, equal to γ = 32 mN/m, it is possible to estimate a disjoining pressure -defined for a dry foam 36 as Π d ≃ γ/rP B -of about 1350 Pa at the end of the experiment. This pressure value in regard to the film thickness is reasonable if it is compared to the values measured for SDS by varying the ionic strength 69 However, to better correlate their variation, thin film pressure balance measurements would be required 70 . Nevertheless if we analyse the variation of the Plateau border radius as a function of time via the image analysis (Fig.…”

Synthesis of d-Gluconic Acetal Surfactants and Their Foaming Behaviors

“…15−19 Although various strategies for modification of hydroxyl groups in gluconic acid were carried out to explore the properties, studies on the formation of hydrogen bonds and the interactions of hydrogen bonds with the dynamics of adsorption and diffusion on surfaces together with the properties have rarely been reported. 20 Herein, for the first time, we designed and synthesized Dgluconic acetal surfactants with bicyclic (G-GAC various −OH groups in gluconic acid (Figure 1). The effects of surfactant structures on the properties of solution, such as the surface activity, critical micelle concentration, foaming ability, and intermolecular interactions, were studied.…”

“…Gluconic acid is a kind of sugar acid with five hydroxyl groups and one carboxyl group, which is feasible to be modified. Recently, many amphiphilic molecules derived from gluconic acid have been reported, which were mainly concentrated on hydrogel properties. − Although various strategies for modification of hydroxyl groups in gluconic acid were carried out to explore the properties, studies on the formation of hydrogen bonds and the interactions of hydrogen bonds with the dynamics of adsorption and diffusion on surfaces together with the properties have rarely been reported …”