Short-range order in extended-chain crystals of polyoxymethylene from a true molecular perspective: An atomic force microscopy study

Atomic force microscopy (AFM) images of extended-chain crystals of polyoxymethylene (POM) obtained in solid-state polymerization have been made to molecular resolution on the surface of the microfibrils which were formed during the topotactic polymerization process. AFM scans with molecular resolution reproduced the expected crystal lattice parameters c = 1.72 nm (X-ray data, c = 1.739 nm) and a = 0.45 nm (X-ray data, a = 0.447 nm). The order of the microfibrils within the crystals was analysed and compared with results obtained previously on mechanically oriented polyoxymethylene by using AFM and wide-angle X-ray diffraction data. For the well ordered surface of the POM crystals, an AFM imaging-mechanism is suggested which assumes that the contact force is controlled by the outermost methylene groups at the imaged surface.