Phase-contrast scanning force microscopy and chemical heterogeneity of GR polysulfone ultrafiltration membranes

The surfaces of three commercial urea formaldehyde polysulfone membranes fr om Dow Denmark (TM) (GR51, GR61 and GR81) are characterised both topographi cally and chemically. Their topography is studied by scanning force microsc opy to obtain the corresponding pore-size distributions, which are in fair agreement with nominal molecular weight cut-offs. The composition of the surfaces of the membranes is analysed by X-ray photo electron spectroscopy. The resulting percentage content of nitrogen, which could be attributed probably to an additive used in the manufacturing proce ss, is shown to correlate with the portion of the total surface with differ ent viscoelastic properties as investigated by using phase-contrast scannin g force microscopy. Both parameters are increasing for membranes with decre asing molecular weight cut-off. Also, the additive seems to be more sparsel y distributed for the membranes with bigger pores, according to fractal ana lysis. Finally, all the membranes are very similarly wettable.