Stability, occurence and step morphology of polymorphs and polytypes of stearic acid
1988; Elsevier BV; Volume: 87; Issue: 2-3 Linguagem: Inglês
10.1016/0022-0248(88)90171-6
ISSN1873-5002
AutoresKimio Inaoka, Masamichi Kobayashi, Masakazu Okada, Kiyotaka Sato,
Tópico(s)Polymer crystallization and properties
ResumoAbstract Surface step morphology of three structural modifications of stearic acid, B(mon), B(orth II) and C(mon), was observed by replica method (TEM). The characteristic simple and interlaced patterns were observed for monoclinic and pseudo-orthorhombic polytypes, respectively. The observation on the C crystals which were transformed from B(orth II) or B(mon) enabled to detect two different modes of lattice displacement involved in composite polymorphic-polytypic transformations from B to C. B(mon) → C(mon) was found to be caused by a collective inclination of the molecules within the lamellar plane followed by the deformation of the subcell of the aliphatic chain, keeping the symmetry-axis unchanged. In contrast, B(orth II) → C(mon) occurs via an alternate rotation of the long-chain molecules in the adjacent lamellae around the c -axis of B(orth II) prototype, keeping the subcell arrangements unchanged. This means that the polytypic structure of a double-layer type was not preserved during the composite B(orth II) → C(mon) transformation. This peculiarity was discussed in terms of the interlamellar instability of a postulated double-layered polytype of the C polymorph.
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