One of the origins for curved edges of polyethylene single crystals
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A new concept of lattice strain was developed to explain the origin of the curved edges of polyethylene (PE) single crystals. In the crystallization of PE from poor solvents, the length of critical nucleus generated is rather short. The thin lamellae are thermodynamically unstable especially at high temperature. Thereby, during the growth of PE single crystals an annealing process is going on simultaneously, which results in a reduction of thickness from the center to growing faces of lamellae. It is known that the thinner the single crystals, the bigger the unit-cell dimensions. Consequently, unit-cells in the central part of single crystals formed are somewhat smaller than those in the outer part of the same crystals. In order to fit in with the gradual enlargement of unit-cell dimensions from the center to the edges of single crystals, the lattice planes of a faster gmwing dominant 110 deform to be a set of parallel arcs of concentric circles. Accordingly, the edge of a slower growing subodinste 200 becomes a part of an ellipse with obvious curvature while the edge of a 11101 sector remains almost straight for it is a part of a Large circumference.
KeywordsPE single crystals curved lateral habit lattice strain
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