Viscoelasticity of interfaces


Question: can you stop coarsening by making interfaces "elastic"? Applications in foods.

Similar problem: stabilize bubbles as ultrasonic tracers

Options: absorb proteins or lipids or nanoparticles to the interfaces

How stable can you make bubbles in this way.

Not only surface rheology matters: the thickness of the protein films is very important.

Cosurfactants can reduce coarsening rates by a factor of 100, but this is not due to 
surface rheology. Solubility of the co-surfactant is crucial, as is the thickness of 
the adsorbed layer, and the liquid fraction.

Gas exchange mostly through films, not Plateau borders, although not in the wet limit.

Basic physics of coarsening: importance of gas solubility. 
Gibbs criterion: "$\partial / partial R ( \gamma / R) >0$ 

Elastic interfaces are not well described by a surface tension.

Important distinction: Ostwald ripening is different, and less well understaood, than 
(dry) foam coarsening

interfaces may have a yield stress.

distinguish Gibb's elasticity from the elasticity of a solid membrane, obtained for 
instance by chemical cross-linking of adsorbed molecules.

surfactants change permeability

constitutive equations for gelled systems? open question!
exist for 3D gelled particule suspensions.
In a non-equilibrium system, there is no hope for a constitutive equn.
How good are the approximations in mena field model(s)?