APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022;
Chicago
Session Y42: Physics and Applications of Foams
8:00 AM–11:00 AM,
Friday, March 18, 2022
Room: McCormick Place W-375A
Sponsoring
Units:
DPOLY DSOFT FIAP
Chair: Kshitish Patankar, Dow, Inc.
Abstract: Y42.00003 : What Is in That Film?
9:12 AM–9:48 AM
Abstract
Presenter:
Yihan Liu
(Dow, Inc.)
Author:
Yihan Liu
(Dow, Inc.)
The collapse of foam via liquid drainage and film rupture have been extensively studied. The current understanding is that many factors critically influence liquid drainage and film thinning including viscosity of the bulk liquid, surface viscosity and elasticity, surfactant transport, disjoining pressure (surface forces), and instability under hydrodynamic and capillary effects. Once the film is sufficiently thin (black film), thermal-induced fluctuation of surfactant concentration can lead to nucleation of a necking hole, the growth of which then completes the film rupture process. The literature on foam stability and its mechanism is voluminous. Many sophisticated measurement techniques have been developed. Most of the experimental data, however, were acquired on well-controlled foams, whereas foam conditions in practical applications are often too complicated to define. The common approach based on the viewpoint of the forces/pressures involved, is not very useful in practice because these various forces―Van der Waals and the electrostatic (treated by the DLVO theory), steric, capillary, etc.―are not easily accessible or known in the application. For a formulator in designing a foam, he/she needs to be able to predict foam stability based on the ingredients added by using a general understanding that can be checked with readily measurable properties. In this talk, a practical approach is presented. This approach is none other than the classical method of using phase behavior to predict film stability against rupture, a practice that has shown tremendous success in predicting liquid-liquid emulsion stability. It focuses on recognizing the structural entity that is most pertinent to the question at hand―the association structure of the surfactant. A case of aqueous foam in the presence of oil as relating to aqueous firefighting foams will be used as an example to illustrate the pragmatism of this approach.