STATIC LIGHT-SCATTERING CHARACTERIZATION OF MICROPOROUS MEMBRANE FILTERS

Some of the more commonly employed microporous membrane filters have b een studied in quasi index matching solvents by means of small-angle s tatic 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 m u m. The high q behaviour of the scattered intensity follows a power l aw I(q) proportional to q(-alpha) where alpha is either 1.9 or 3.8 dep ending on the membrane chemical composition. Such values reveal that o n 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 indicate s 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 Lambda = 2 pi/q(m) is always large r than the pore size and it is not trivially related to it. In particu lar, for membranes made of mixed-esters of cellulose, Lambda is found to be roughly proportional to p(s) for small pore sizes, while for p(s ) > 1.2 mu m it increases only slightly with the pore size and eventua lly tends to saturate. In conclusion, these results indicates that sma ll-angle static light scattering promises to be a very useful techniqu e for characterising microporous membrane filter morphology, and also for quality control.