Determination of surface and bulk pore sizes of flat-sheet and hollow-fiber membranes by atomic force microscopy, gas permeation and solute transport methods

Surface and bulk pore sizes of various polyetherimide flat-sheet and polyvinylidene fluoride hollow-fiber membranes were determined. To obtain the bulk pore size, the solute transport method and gas permeation test were used, whereas the surface pore size was studied by atomic force microscopy (AFM). The gas permeation test was conducted using nitrogen as the standard gas, while the solute transport was performed using aqueous solutions of polyethylene glycol and polyethylene oxide of various molecular weights. Both the mean pore size and pore size distribution were determined. The pore size of both the internal and the external surfaces of hollow-fiber membranes, as well as the pore sizes of the top and the bottom surfaces of flat-sheet membranes, were evaluated using AFM. The techniques used to determine the surface and the bulk pore size can be considered as complementary methods rather than competitive to analyze the entire pore size structure.