Amorphous surface layers in polyethylene single crystals
| Autor: | Anton Peterlin, Hans Gerhard Zachmann |
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| Rok vydání: | 2007 |
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| Zdroj: | Journal of Polymer Science Part C: Polymer Symposia. 34:11-17 |
| ISSN: | 1935-3065 0449-2994 |
| DOI: | 10.1002/polc.5070340104 |
| Popis: | Density, heat of fusion and melting temperature data of annealed polyethylene single crystals suggest the existence of a temperature-dependent pseudo-amorphous surface layer which contains chain folds and free chain ends. In the ideal two-phase model, one assumes two such amorphous layers of thickness l/2 each on the two (001) surfaces of the crystalline core of thickness D = L -l, where L is the total thickness of the single crystal. The thickness of such a layer was calculated under the assumption of random length loops and cilia (free chain ends) for the case of adjacent reentry and of a Maxwellian distribution of loop width. The excess energy requirement of the shortest loops with the high concentration of gauche conformations favors longer loops and hence increases the surface layer thickness. The reduction of entropy by the restrictions imposed by finite loop width and the availability of a half space only acts in the opposite direction. The calculated thickness depends on the true supercooling ΔT = Tm° - T if L is kept constant and on relative supercooling ΔTrel = Tm-T, where Tm is the actual melting point of the crystal, if the crystal core thickness D is kept constant. A qualitative agreement between theory and experiment on this basis seems possible by proper consideration of the contribution of loops and cilia. |
| Databáze: | OpenAIRE |
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