Surface relief, phase and surface potential investigations of composite polymer membranes using AFM

Composite membrane consisting from two different polymers - SPEKK and PVDF was used as two-phase sample for investigations with atomic force microscope (AMF). Three AFM modes were applied to analysis - surface relief, phase and surface potential scanning. Theoretical advantage of all three methods used for same sample is possibility to provide more detailed information on different phases in material. AFM results of surface investigation for pure SPEKK showed small fluctuation in height and phase (only difference in some nm and about 5°), what means that material is homogeneous. We found that for composite polymer membrane sample the changes in both modes are much more significant: for height it reaches 600 nm, but for phase - 20°. If surface potential of composite polymer sample clearly identifies some areas as SPEKK polymer, than in topography and phase images these places are identified as PVDF polymer only. This can be explained with the fact that polymers dissipate charge not only from surface but also little in depth. Even with such small potential contrast the surface potential mode of AFM can be used to detect distinct polymer structures not only on surface but also in a volume under the surface.