ATOMIC FORCE MICROSCOPY OF POLYMER CRYSTALS .6. MOLECULAR IMAGING AND STUDY OF POLYMORPHISM IN POLY(P-PHENYLENETEREPHTHALAMIDE) FIBERS

The macromolecules in extended-chain crystals of as-spun and annealed poly(p-phenyleneterephthalamide) fibers and the microfibrillar morphology were visualized by atomic force microscopy (AFM). Quantitative information about the crystal lattice on the surface of the fibrils was obtained. The positions of the phenylene groups with respect to the hydrogen-bonded sheet of the crystal lattice were visualized. Results are compared with structures deduced from X-ray diffraction measurements on one hand, and from predictions for polymorphic forms of the crystal structure calculated in computer simulation experiments on the other. Periodicities and registration angle obtained for annealed fibers are consistent with reported crystal modifications. Analyses of images captured on as-spun fibers indicate the existence of a new polymorphic form (modification III) which was suggested by computer simulations but has not been previously observed experimentally. The AFM image of this new structure is consistent with successive phenylene rings along the chain being rotated in similar, rather than opposite, directions about the chain axes.