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Soft Matter and Biological Physics


Eur. Phys. J. E 8, 289-297 (2002)
DOI: 10.1140/epje/i2002-10015-3

Branched crystal morphology of linear polyethylene crystallized in a two-dimensional diffusion-controlled growth field

F. Zhang, J. Liu, H. Huang, B. Du and T. He

State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Science, Changchun, Jilin, 130022, PRC

tbhe@ns.ciac.jl.cn

(Received 15 March 2002 and Received in final form 29 April 2002)

Abstract
The branched crystal morphology of linear polyethylene formed at various temperatures from thin films has been studied by atomic-force microscopy (AFM), transmission electron microscopy (TEM), electron diffraction (ED) pattern and polymer decoration technique. Two types of branched patterns, i.e. dendrite and seaweed patterns, have been visualized. The fractal dimension $d_{\rm f} = 1.65$ of both dendrite and some of seaweed patterns was obtained by using the box-counting method, although most of the seaweed patterns are compact. Selected-area ED patterns indicate that the fold stems tilt about 34.5 $^{\circ}$ around the b-axis and polymer decoration patterns show that the chain folding direction and regularity in two (200) regions are quite different from each other. Because of chain tilting, branched crystals show three striking features: 1) the lamella-like branches show two (200) regions with different thickness; 2) the crystals usually bend towards the thin region; 3) the thick region grows faster by developing branches, thus branches usually occur outside the thick region. The branched patterns show a characteristic width w, which gives a linear relationship with the crystallization temperature on a semilogarithmic plot.

PACS
61.41.+e - Polymers, elastomers, and plastics.
68.55.-a - Thin film structure and morphology.
81.10.Aj - Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation.


© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002