MICROPOROUS MEMBRANE FILTERS - A STATIC LIGHT-SCATTERING STUDY

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.