Atomic force microscopy characterization of ultrafiltration membranes: correspondence between surface pore dimensions and molecular weight cut-off

Atomic force microscopy (AFM) has been used to quantify the mean surface pore diameters of a family of five ultrafiltration membranes with molecular weight cut-off (MWCO) in the range 1000-10 000, High aspect ratio tips were used and the images were treated with fast Fourier transform filtering to remove distortions. The mean pore diameters were found to be in the range 1.93-3.14 nm, increasing systematically with the MWCO. Mean pore diameters have also been evaluated from the MWCO values using three published expressions relating MWCO to solute radius. Depending on the expression used, the ratio of the mean pore diameters obtained from MWCO data and AFM measurements (R-r) was in the range 1.04-2.42. Agreement between the diameters obtained in the two ways was best for the membranes with the lowest MWCO values. The overall agreement was substantially better than has been reported previously. The good correspondence between mean surface pore dimensions and MWCO demonstrates the usefulness of AFM in quantifying such a keg membrane property. Copyright (C) 2000 John Wiley & Sons, Ltd.