Izlaganje sa skupa

Crystalline Amorphous Interfaces in Polymer Crystals

A. Peterlin ; Camme Dreyfus Laboratory, Research Triangle Institute, Research Triangle Park North Carolina, 27709, U.S. A.

Sažetak

Crystalline polymer solids are never ideally crystallized. From
the density defect one may formally derive a finite crystalline
and amorphous component. The study of polyethylene single crystals
by different methods suggests a spatial separation of the
components: a crystalline core and two quasi amorphous surface
layers containing the chain folds. At the interface the amorphous
loops are fixed in the crystal lattice. The space requirement of
the amorphous conformations can be only met by the assumption
of varying loop length . . This immediately increases the entropy
content of the loops and partly compensates for the reduction
caused by the loop ends fixed at the interface and by the limitation
of space accessible to the loops by the existence of the
crystal lattice. The high energy requirement of the shortest loops
with an excess of gauche conformations favors large loops and
hence increases the thickness of the surface layer. The values
obtained for strictly adjacent reentry of all loops are still below
the experimental data. A perfect fit seems possible if one assumes
that there are a few loops with nonadjacent reentry and some chains
with one end free. The former are a consequence of crystallization
kinetics and the latter result from the finite number of extremely
long loops surpassing the length of single molecules but also from
the chain ends of all molecules of the sample because there is a
clear tendency of their concentration on the surface of the crystal.

Ključne riječi

Hrčak ID:

197557

URI

https://hrcak.srce.hr/197557

Datum izdavanja:

20.8.1970.

Posjeta: 697 *