Atomic force microscopy on polymers and polymer related compounds

Summary

The largest surfaces of lozenge-shaped monocrystals of polymer 2,4-hexadiynylene bis(p-fluorobenzenesulfonate), (pFBS), and its monomer have been studied by Atomic Force Microscopy (AFM). Tridimensional maps of interatomic forces between probe and surface have been recorded at areas from hundreds of nanometers down to the atomic scale. The examined surfaces, which generally correspond to the crystallographic [100] plane, are built from end groups of substituents, benzene rings, with main planes being perpendicular to the surface. Large scale AFM images reveal a fibrillar structure of the polymer surface in contrast to a not well-defined morphology of the monomer surface. The atomic scale maps of polymer and monomer [100] surfaces look quite similar. They can be characterized by alternating rows of ‘hills’, one of which shows zig-zag type arrangement. The repeat distances along the rows are .53±.04 nm for the polymer and .61±.06 for the monomer. In the close to perpendicular direction — α=89.5±3.0^o for the polymer and the monomer — the repeat distances are 1.62±.16 nm for the polymer and 1.47±.08 nm for the monomer. These values are in general agreement with the crystallographic parameters, b=.4914 nm, c=1.4103 nm (polymer), and b=.5187 nm, c=1.4093 nm (monomer). The appearance of alternating rows in AFM images does not exactly correspond, however, to the surface atomic arrangement in the [100] plane, which has been reconstructed from the crystallographic data. Though the AFM patterns might be assigned to —CF-CH- groups of substituents, the differences found between images and diffraction data are discussed.