Measure coarsening without confinement

(enclosing foam in a box was not advised)

Need for a practical way to measure development of foam

Check the bulk without disturbance
Answer could be DWS or neutron scattering:

 - no change of angle dependence

 - multiple scattering comes close to diffusion of photons

 - l* - length/number of scattering of photons to a state when no scattering
   can be reconstructed

 - L* typical length for foams; somehow related to bubble size.
It has to be correlated to actual bubble size by oher means (microscope)
Can be related to refraction of light.

Do you need tracer particles for DWS?
No only to measure viscosity and correlate shift of scattering due to movements in a 
rheological sample

A problem arises in the deduction of L* because optical image analysis is possible only 
inconfined geometry

To which power does the average bubble size contribute to L*?

Correlate L* to bubble size by very regular foams made with mnicrofluidics devices!
Highly ordered foams with known geometry should answer that question.

Appearance of echos in the correlation function -> correlated to elasticity of the foam 
and maybe due to catastrophic events.




Later note from short presentations on Friday:

Diffusive light scattering is interpreted in terms of transport mean free 
path which is simply proprtional to bubble size only if constant liquid 
fraction is maintained. In such a case, there is (at least approximately) 
only a single length scale in the structure. More generally, the mean free 
path depends on liquid fraction as well - but some simplicity is restored 
if refraction by Plateau Borders only is assumed to operate. A simple 
scaling results from this model, at least in the dry regime, which some 
data support.