Characterization of Polymer Surfaces with Atomic Force Microscopy

Applications of state-of-the-art atomic force microscopy methods to the elucidation of the surface and near-surface structure of polymeric solids are described. Contact, tapping, force modulation, frictional force, and other modes of atomic force microscopy are described, and recent results are summarized. Conformational and chain order, crystalline order, polymer crystals, lamellar structures, lamellar surfaces, fold surfaces, and fibers and films with highly oriented molecules all yield important information. Controlled deformation of polymer surfaces, both reversible and irreversible, with the atomic force microscope, provides a wealth of information about mechanical properties on a nanometer scale. The observation of phase-separated regions and of polymer crystals lying below a smooth surface shows that not only topography but also elastic inhomogeneity can be observed in great detail with the atomic force microscope. This is a rapidly developing field, and some indications of future developments are presented. PROBING SURFACES WITH AFM Scanning probe microscopy constitutes a family of advanced techniques for surface analysis (1a,b,c). Although scanning tunneling microscopy (STM) was invented first, the current progress in scanning probe microscopy of polymers is largely in the development of atomic force microscopy (AFM). The universal character of the repulsive forces between the tip and the sample, which are 175 0084-6600/97/0801-0175$08.00 P1: NBL/SDA/MKV P2: SDA/PLB QC: SDA June 5, 1997 13:7 Annual Reviews AR034-07 176 MAGONOV & RENEKER employed for surface analysis in AFM, enables the examination of a practically unlimited range of materials. After being introduced as the analogue of STM for the high-resolution profiling of nonconducting surfaces, AFM has developed into a multifunctional technique suitable for characterization of topography, adhesion, mechanical, and other properties on scales from hundreds of microns to nanometers. Polymeric materials, which play an important role in modern technology, have been examined by AFM (2a,b,c). An increasing technological interest in polymer properties at the nanometer scale emphasizes the importance of AFM applications to polymers.