The analysis presented in the previous section was performed on artificially aged membranes, which were not fouled. Typical SEM images of fouled membranes obtained with different sample preparation and imaging parameters are presented in Fig. 11. The images suggest that the surface roughness of the fouled membranes coated with gold was greater than that observed when fouled membranes were coated with iridium, regardless of the sample preparation or imaging parameters considered. The surface roughness of membranes imaged with a mixed detector (Fig. 11b and c) or a 30° tilt angle (Fig. 11b and e) appeared to be greater than for those imaged with an upper detector (Fig. 11e and f), or a 0°tilt angle (Fig. 11c and f). The above observations are consistent with those for artificially aged membranes and indicate that all of the sample preparation and imaging parameters considered affect the SEM images and the conclusions that can be drawn from these images. When imaging naturally aged membranes with SEM, at least some of the membrane pore structure generally cannot be observed, as it is typically covered with an irreversible surface foulant structure, especially when dealing with relatively old membranes such as those used in the present study. Although no quantitative information can be obtained from the images of these heavily irreversibly fouled membranes, similar trends (i.e. effect of sample preparation and imaging parameters on the properties of interest) to those obtained when imaging artificially aged membranes are expected when imaging less irreversibly fouled membranes.