charge densities of both the gel phase and the fluid phase be equal. We used Fluid
Electric Force Microscopy (FEFM) [45] to compare surface charge densities of the two
phases. FEFM involves the AFM scanning the sample topography, lifting the tip to a
predetermined lift height and rescanning the along the same contour, at the lift height (see
Figure 3.15). For flat samples, the force on the tip during the lift scan is directly
proportional to the samples surface charge density. Thus using FEFM we get a
simultaneous topography and charge contrast map.
F ∞ °sample
Figure 3.15: Schematic of Fluid Electric Force Microscopy (FEFM). The force F
experienced by the tip during the lift scan is directly proportional to the samples surface
charge density σsampie.
44