Regensburg 2004 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 16: POSTER: Computational Physics, Complex Systems

CPP 16.20: Poster

Dienstag, 9. März 2004, 17:00–19:00, B

Single Molecule Diffusion under Confinement and Shear — •Arne Schob und Frank Cichos — Institut für Physik 123705, TU Chemnitz, 09107 Chemnitz

Liquids at solid surfaces may show a completely different structure compared to the bulk structure, since they may form a layering structure parallel to the surface. Such a structural difference immediately implies dynamical differences, which shows up in an anisotropic Brownian motion or even in a different shear viscosity. An understanding of this behavior is a key to understand lubrication and friction on a molecular scale. We employ fluorescent dye molecules to measure molecular mobility in ultrathin liquid films confined between two atomically flat surfaces. We use highly doped liquid films to measure the film thickness as a function of applied force. In this way we are able to calibrate our setup for single molecule experiments and to compare our results with other publications. Single molecules are tracked with a wide field fluorescence microscope coupled to a surface forces apparatus. The experiments show, that corresponding to measurements on free liquid films the diffusion of molecules is slowed down due to the interaction with the solid interface. We are further able to apply shear to the liquid film by moving one of the confining solid surfaces. By seperating their diffusive motion from the shear-driven motion, we have acces to the velocity within the sheared liquid on a molecular scale.