Foams in highly viscous liquids
Un article de Surface du verre et interfaces.
Franck Pigeonneau, Emmanuelle Gouillart
Foams -- coarse dispersions of gas in small amounts of liquid -- are present in a wide variety of applications. Certain characteristics of foam are desired for particular applications, e.g. shampoos or shaving creams. In other processes, too much foam has to be avoided, as for machine laundering or distillation.
The glass melting process creates a large quantity of bubbles, that can lead in some cases to a thick foam layer on the surface of the glass bath. This foam decreases the energetic efficiency and the productivity of the furnace. Hence, insights into the stability of viscous foams is valuable. We expect the foam stability to depend on the chemical composition of the liquid, surface rheology, diffusion of gas, and thermal transferts.
We study foam both on the local scale -- what are the dynamics of liquid drainage for a single glass film ? -- and at the batch level -- how does a glass foam evolve with time ?
We have launched experiments devoted to the lamella stability of viscous liquids. Currently, optical measures of film stability are conducted with PDMS films at room temperature. In the near future, we wish to extend such measures to molten glass in a laboratory furnace (see picture above). We have observed oustanding stability of glass films that cannot be deduced from purely hydrodynamical models. Modifications of the chemical composition of the film surface might be responsible for this phenomenon: this hypothesis is currently under investigation.
The second point of our activities concerns foam drainage. We work on models where the coupling between thermal process and drainage are taken into account. Regarding future experiments, we also work on developing a generator of bubbles that will allow to study an entire foam, first in model liquids at room temperature, and later in a glass bath.
For further details, contact Franck Pigeonneau at franck.pigeonneau AT saint-gobain.com