Slide 5 of 12
Notes:
The most critical element of FI-AFM is the description of interfacial deformation.
Until now, the linear adjustment of distance with force was assumed to be sufficient; but our experiments show that it is necessary to match the drop deformation with solutions to the augmented Young-Laplace equation for quantitatively meaningful results.
The drop profile is described by the curvature term in brackets, simplified for axisymmetry.
The pressure drop across the interface is proportional to the curvature by the value of the interfacial tension. This Laplace pressure is balanced by the sum of surface and body forces acting on the interface: the disjoining pressure, the internal drop pressure and gravity.
The effective stiffness of the interface increases with deformation such that no simple function properly describes the F(z) relationship. Empirically, it is a variable power function with a linear limit at extremely low force.