We studied some of the more employed microporous membrane filters via
small-angle static light scattering under quasi-index matching conditi
ons. We report data from both acetate of cellulose (AC) and mixed-este
rs of cellulose (MEC) membranes of various pore sizes p(s). On short l
ength scales, the membranes have fractal morphology. While AC filters
may be described as surface fractals, MEC membranes turn out to be mas
s fractals. Furthermore, the scattered intensity distributions exhibit
a peak at a finite wave vector q(m), thus indicating the presence of
a certain degree of spatial order over a characteristic length Lambda
= 2 pi/q(m). Lambda is found to increase with p(s), as expected, altho
ugh it is always larger than p(s) and is not trivially related to it.
We propose a description of the membrane structure which accounts for
the experimental results and is further corroborated by mass density m
easurements.