Characterisation of nanofiltration membranes using atomic force microscopy

Atomic force microscopy (AFM) has been used to characterize five commercial nanofiltration (NF) membranes from three companies. High-resolution 3D images of the membranes were obtained without preparative treatment that may affect the membrane surface. Obtained images have been filtered to overcome the effect of tip convolution and the noises. Two sizes of the images were obtained 2 μm × 2 μm and small sizes. The first images were used to find the surface morphology data such as average roughness, mean height, root mean square (RMS), and maximum peak-to-valley. The small size images showing visible pores were used to determine the pore size and pore size distributions, which were used to calculate porosity of membranes. A fitted line using lognormal distributions was used to represent the pore size distribution of the nanofiltration membranes. The results show that the lognormal distribution is fitted well with AFM experimental data.