Once a sample that had gel and fluid patches of equal charge density, as measured by
FEFM, was obtained, force curves were recorded over both the gel phase lipid patches
and also on adjacent fluid phase regions following the method described in Section 2.2 of
this thesis. By taking force curves in the same region, in the same experiment, we are
able to interpret any variations in the gel and fluid force curves in terms of the relative
mobility of each phase and are also able to minimize any effects caused by variability in
AFM tips and electrolyte concentrations. The raw force curve data was processed using
the methods described in Section 2.2 and converted into force as shown in Figures 3.18.
Figure 3.18: Comparison of force curves taken over fluid phase (Blue curve) and gel
phase (Red curve) shown with a constant surface charge electrostatic fit (Black dashed
curve). Both sets of data were taken with the same tip during the same experiment and
the electrostatic fit was obtained for a surface charge density of -0.04 C∕m2.
In Figure 3.18, the force over the fluid phase (shown in blue) is lower than that over the
gel phase (shown in blue), at tip separations less than 7 nm. This, in addition to the
previous data, suggests that the tip induced mobile lipid charge regulation is more
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