AFM images of the cross-section of polyetherimide hollow fibers

The morphology of the cross section of polyetherimide hollow fiber membranes prepared at different air gaps were studied by the tapping-mode atomic force microscopy (TM-AFM). Samples were prepared by cutting the hollow fiber with a sharp edge at room temperature or by at liquid nitrogen temperature. No significant differences were observed on the morphology of the cross sectional samples prepared by the two different methods. However, by fracturing the hollow fiber at liquid temperature the surface of the cross-section became rougher, limiting the cross sectional area available to study by AFM. It was observed that the nodules in the cross-section were aligned in the angular direction and the layer of nodules near the inner surface (active layer) were well defined and compactly packed in comparison with the nodules near the outer surface, where the nodules were fused forming a porous structure.