Studies of High Performance Fibers by Atomic Force Microscopy and Molecular Simulation
Atomic force microscopy (AFM) images obtained from cleaved surfaces of both as-spun and annealed fibers of poly(p-phenylene terephthalamide) (PPTA) have been interpreted with the aid of results from molecular simulations and wide angle X-ray scattering (WAXS). Angstrom-scale periodicities observed in AFM images of the annealed fiber are in accord with those reported in the literature based on WAXS data. For the as-spun fiber, AFM confirms the presence of at least two polymorphs. Among these, a new lattice structure is observed, which has eluded deconvolution from experimental X-ray data. This new lattice exhibits chain conformations and hydrogen bonding structure which is distinct from that seen in either of the two previously reported crystal modifications of PPTA. Interpretation of the AFM images in this case is greatly facilitated by the independent data from molecular simulations. The new crystal facet observed is fully consistent with a third crystal modification previously suggested by molecular simulation.
KeywordsAtomic Force Microscopy Atomic Force Microscopy Image Draw Ratio Molecular Simulation Lateral Periodicity
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