ATOMIC-FORCE MICROSCOPY FOR ULTRAFILTRATION MEMBRANE IMAGING

Atomic force microscopy (AFM) can reveal nanometer-scale structure of samples without the sample preparation techniques that involve dehydra tion. This is particularly important for hydrophilic organic materials . An asymmetric polysulfone ultrafiltration membrane (molecular weight cutoff rated at 10 kg/mol) was imaged by AFM. Sample mounting methods tried include cyanoacrylate, double-sided tape, and paraffin. Wax and tape bonding did not lead to usable images. Cyanoacrylate bonding res ulted in images that appear to show 2.8 x 10(9) pores/m(2) approximate ly 3 nm in diameter, creating a porosity of 2%. This is consistent wit h estimates of molecular sizes for 10 kg/mol proteins, but not with th e results of other AFM studies of similar membranes. The discrepancies can be explained largely by differences in sample preparation techniq ues.