We
carried out large-scale atomistic molecular dynamics simulations
to study the growth of twin lamellar crystals of polyethylene initiated
by small crystal seeds. By examining the size distribution of the
stems—straight crystalline polymer segments—we show
that the crystal edge has a parabolic profile. At the growth front,
there is a layer of stems too short to be stable, and new stable stems
are formed within this layer, leading to crystal growth. Away from
the edge, the lengthening of the stems is limited by a lack of available
slack length in the chains. This frustration can be relieved by mobile
crystal defects that allow topological relaxation by traversing through
the crystal. The results shed light on the process of polymer crystal
growth and help explain initial thickness selection and lamellar thickening.
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