Atomic force microscopy in structured liquids: remark on the interpretation of jumps in force curves

When analysing solvation forces measured with the atomic force microscope (AFM), the concept of disjoining pressure and Derjaguin's approximation are usually used. In contrast, characteristic jumps observed on single layers (such as surfactant layers or biological membranes) are interpreted as a rupture process. We argue that both interpretations are not a priori clear. Force curves showing multilayers might, for example, reflect the subsequent rupture of individual layers. In force curves measured on single molecular layers, the jump distance is usually taken as the layer thickness. Here, we demonstrate that this is not necessarily true and that real layer thicknesses can be significantly larger than the observed jump-in distance.