Friction and Surface Dynamics of Polymers on the Nanoscale by AFM

In this article the measurement and understanding of friction forces and surface dynamics of polymers on the one hand and the importance of molecular relaxation processes and viscoelasticity in polymers for advanced micro- and nanoscale applications on the other hand are discussed. Particular attention is paid to the nanoscale (surface) analysis by scanned probe microscopic approaches, including atomic force microscopy (AFM), as a means to assess molecular relaxation processes that operate at a given temperature. Established AFM approaches, including lateral force and force modulation microscopy, are introduced and more recently developed techniques, such as torsional resonant modes, are briefly sketched. On the basis of the discussion of the techniques to measure friction and to probe surface dynamics of polymers on the nanoscale, illustrative examples are reviewed. The examples discussed address in particular the determination of values of the glass transition temperature (T g) and the difference of T g assessed in the bulk vs. at the free surface of polymers. Confinement and thin film effects on T g, but also on sub-T g transitions and chain dynamics, are treated in detail. Finally, the mapping of multiphase systems and anisotropic friction receive attention