ISSN:
1435-1536
Schlagwort(e):
Cycloalkanes
;
phase transitions in oligomers
;
electron diffraction
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Chemie und Pharmazie
,
Maschinenbau
Notizen:
Abstract The structure and thermal behavior of long-chain cycloalkanes (CH2)n with n= 48, 72, 96, 144 and 288 have been investigated by electron diffraction, WAXS and SAXS analysis. Five different modifications have been characterized by their subcells as a function of ring size, crystallization conditions and temperature. The rings adopt, in all modifications, a conformation with two straight stems connected by folds. Similarity with the polyethylene lattice is achieved only for n≥144. In this case, the stems are perpendicular to the layer surface and pack in the well-known orthorhombic subcell regardless of whether the rings are crystallized from solution or melt. (CH2)96 forms the same type of subcell when crystallized from the melt, but the stems are oblique to the layer surface. Rings of all sizes undergo a transition into a phase in which the stems are arranged similarly as in the “rotator phase” of linear paraffins. (CH2)72 and (CH2)96 exhibit additional transitions at lower temperatures. One significant feature of some transitions is the change of conformation and length of the folds.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF01457258
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