The name is absent

3.3 Results
3.3.1 Van der Waals interaction

The model given in Chapter 2 makes several assumptions regarding the behavior of the
lipid surface. In particular, it does not account for the perturbations of the lipid surface
due to the presence of the AFM tip. While neglecting the effect of the AFM tip might be
valid at longer distances, at shorter distances, the presence of the charged tip may have an
effect on the lipid surface potential. In addition, the previous model does not account for
van der Waals attractions.

For a sphere-plane geometry, the van der Waals force ( F) is given by [16, 78-80]

A_hR

^F-6^

Where X is the distance between the surfaces, R is the radius of the sphere and A∏ is the

Hamaker constant [81]. We have used the sphere-plane approximation thus far and
continue to do so in this calculation. We use the experimentally measured value of the
AFM tip radius as R. The value of the Hamaker constant was calculated to be 2 x 10^²° J
[82, 83]. In doing the above calculations, we assume that the electric double layer forces
and the van der Waals forces are independent and can be added [26].

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