PARTICLE SIZING BY PHOTON-CORRELATION SPECTROSCOPY .4. RESOLUTION OF BIMODALS AND COMPARISON WITH OTHER PARTICLE SIZING METHODS

The practical performances of single and multi-angle photon correlatio n spectroscopy (PCS) for resolving bimodal distributions of industrial poly (methyl methacrylate) samples was investigated in a comparative study by several users affiliated to academic and industrial groups an d by two suppliers of commercial equipment. The results for the harmon ic intensity averaged diameters obtained by cumulants analysis reporte d by the different laboratories are in agreement, in addition to the r esults for the normalized second cumulants. The uncertainty on the lat ter quantities is large, however. For the bimodal samples with two pop ulations with average diameters in a ratio of about 2.5: 1, not all us ers were able to resolve the distribution in its components by single- angle PCS. Some slight improvement was obtained by multi-angle PCS. Ot her indirect techniques (polarization intensity differential scatterin g, static light scattering data and disc photosedimentometer) appeared to be superior for resolving the bimodal distributions.