Soft Matter and Complex Systems Seminar

Imaging of deformable surfaces with the help of the Atomic Force Microscope (AFM) is performed mainly in the non-contact mode, in which the tip of the AFM oscillates above the surface of the sample. If the tip approaches the sample too much the jump-to-contact phenomenon can occur,which creates a capillary bridge between the sample and the tip. This can disturb the measurements significantly and needs to be avoided. Equilibrium predictions of the surface deformation give an estimate on the minimum distance at which the tip can approach the liquid surface. However, it appears that the dynamic effects are of great importance in this problem and need to be taken into account.
I will introduce a systematic theoretical model of the liquid film dynamics, which reveals the relevant time scales and predicts deformation of liquid films interacting with a nano-sized objects. The model simplifies to the lubrication approximation in the case of very thin films, which was recently analyzed in the literature. I will show how different parameters of the tip oscillations influence the surface deformation and that the restriction to the lubrication approximation can lead to noticeable errors even for relatively thin films.