In atomic force microscope studies of thin films often a defined jump of the tip through the film is observed once a certain threshold force has been exceeded. In particular, on lipid bilayers this is regularly observed. In a previous paper [H.-J. Butt and V. Franz, Phys. Rev. E 66, 031601 (2002)] we presented two complementary models to describe film rupture. The aim of this study was to verify these models. Experiments were done with solid supported bilayers consisting of dioleoyloxypropyl-trimethylammonium chloride (DOTAP) and dioleoylphosphatidylserine (DOPS) in aqueous solutions and with propanol. Both models describe experimental results adequately. In particular, a narrow distribution of yield forces and an increase of the mean yield force with increasing loading rate is correctly predicted. For the lipid bilayers spreading pressures of roughly 20 mN/m (DOTAP) and 5 mN/m (DOPS) were measured. Line tensions for the edge of a lipid bilayer ranged between 3 (DOTAP) and 6 pN (DOPS).

The force profile between a glass microsphere and mica in 1-propanol has been measured with the colloidal probe technique. Oscillatory solvation forces indicate a layered structure of the confined propanol for at least three layers. In the same experiment, hydrodynamic forces were measured at high approaching velocity. Comparing measured force curves with calculations we found a significant effective slip, which could be described by a slip length of 10–14 nm.

The adhesion of solid surfaces across polymer melts has been studied with an atomic force microscope (AFM). As polymers we used poly(dimethylsiloxane) (PDMS, Mw ) 18 000), poly(ethylmethylsiloxane) (PEMS, Mw ) 16 800), and a diblock copolymer (PDMS-b-PEMS, Mw ) 15 100). Upon retraction, adhesion peaks were observed which we interpret as bridging of single polymer chains. Bridging occurred seldom (in each 20th force curve) in PDMS and more often in PEMS (in each 8th force curve) and was most prominent in the diblock copolymer, where a typical force curve contained 5-10 adhesion peaks. The mean detachment force decreased with increasing retraction velocity, indicating that the bond to the surface or tip is not a direct contact with the solid surface.