Résumé
Some of the more commonly employed microporous membrane filters have been studied in quasi index matching solvents by means of small-angle static light scattering. We report data obtained from membranes made of esters of cellulose with rated pore size
p
s ranging from 0.1 to 8 μm. The high
q behaviour of the scattered intensity follows a power law
I(
q)
α
q
−
α
where α is either 1.9 or 3.8 depending on the membrane chemical composition. Such values reveal that on a short length scale the filters have a fractal nature. Furthermore, the scattered intensity distribution exhibits a peak at a finite wave vector
q
m, like in spinodal decomposition processes (which indicates mass anticorrelation effects), a behaviour similar to that observed in Vycor porous glasses via neutron and X-ray small angle scattering. The peak position moves towards smaller
q values when increasing
p
s although the characteristic length
Λ =
2π
q
m
is always larger than the pore size and it is not trivially related to it. In particular, for membranes made of mixed-esters of cellulose, Λ is found to be roughly proportional to
p
s for small pore sizes, while for
p
s > 1.2
μm it increases only slightly with the pore size and eventually tends to saturate. In conclusion, these results indicates that small-angle static light scattering promises to be a very useful technique for characterising microporous membrane filter morphology, and also for quality control.