Maximal pore size in UF membranes

The ultrafiltration membrane rejection capability is most often characterized by molecular weight cut-off (MWCO). The value is found by rejection of organic solutes and the evaluation of particle retention requires a conversion of either MWCO to pore size or particle diameter to molecular weight. The conversion affects the accuracy of reported values and results in a gap between reported and measured retentions.We suggest a novel, simple and effective pore size test based on synthesis and membrane transfer of rigid nanoparticles. Gold and silver 3-50nm monodispersions had delivered a comprehensive pore size distribution including d ₁₀₀, a pore diameter for which a membrane has a 100% retention capability. The maximal pore size in UF membrane structure can hardly be detected with other methods although it is much needed for precise separation analysis.The d ₁₀₀ values in tested UF membranes vary between 40nm and 50nm depending on the membrane material. The polymer membranes are more flexible than the ceramics and their d ₁₀₀ is usually much higher than MWCO. The d ₁₀₀ increases with high transmembrane pressure or after oxidative chemical cleaning. For some membranes the d ₁₀₀ values can be correlated with d ₉₀ but not with d ₅₀.