Lamellar crystals, microscopy determination

Disregarding any detailed morphological models proposed for the lamellar crystals in semicrystalline polymers in the past half centiny, crystal imit cells in semicrys-talUne poisoners exactly obey the rules of classical crystallography, which consist of 7 crystal systems and 14 Bravais lattices (more precisely, there are only 6 crystal systems in polymer crystals, and the cubic system does not exist). Most of the unit cell determinations of the semicrystalline polymers rely on the wide-angle x-ray diffraction (waxd) experiments on oriented poisoner fibers and films. This is be-canse of small crystal sizes in polymers, which lead to a difficult experimental task to obtain single-crystal waxd results on semicrystalfine polymers. It is also possible to nse electron diffraction (ed) method in transmission electron microscopy (tern) to determine polymer lamellar crystal unit cell structures, dimensions, and symmetries. 

The lamellar liquid crystal region was determined by microscopy with samples between crossed polarizers and their extension confirmed by low-angle X-ray diffraction. 

When macromolecular cholesteric liquid crystals were imaged, a twisting of molecular orientation, which translated into a periodic lamellar structure in the materials, was foimd. Good agreement between afm and tern (transmission electron microscopy) was obtained in determining the widths of the lamellae. When the same polymer was processed from an isotropic solution, a homogeneous and nodular structure, lacking the periodicity of the cholesteric structure, was obtained (107). 

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