title: Molecular-weight-dependent changes in morphology of solution-grown polyethylene single crystals.
abstract: Polymer single crystals consisting of folded chains are always in a nonequilibrium state, even if they are faceted with a well-defined envelope reflecting the parameters of the crystal unit cell. Heterogeneities like small variations in the degree of chain folding within such crystals are responsible for a rather broad range in melting temperature. Consequently, upon annealing at a given temperature, some parts may be above and some below their respective melting temperatures, inducing a lamellar thickening process, which may vary locally. To emphasize such variations, controlled annealing experiments are performed at comparatively low temperatures and for long times. For single crystals of low-molecular-weight polyethylene, the formation of the well-known "Swiss-cheese"-like morphology with randomly distributed holes of varying sizes within the annealed single crystal is observed. However, for high-molecular-weight polyethylene, a regular pattern appeared upon annealing, characterized by branches of equal width that are oriented perpendicular to the crystal edge. All branches end at the nucleation site. Interestingly, the resulting pattern depends sensitively on both crystallization and annealing conditions. These thermally induced regular patterns within a single crystal are attributed to a stable crystalline framework formed within polyethylene single crystals in the course of growth.
authors.affiliation: Institute of Physics, University of Freiburg, 79104, Freiburg, Germany; Hermann Staudinger Graduate School, University of Freiburg, 79104, Freiburg, Germany; School of Materials Science & Engineering, Zhengzhou University, Zhengzhou, 450002, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Zhang
authors.forename: Jingbo
authors.initials: J
authors.lastname: Chen
authors.forename: Moritz C
authors.initials: MC
authors.lastname: Baier
authors.forename: Stefan
authors.initials: S
authors.lastname: Mecking
authors.forename: Renate
authors.initials: R
authors.lastname: Reiter
authors.forename: Rolf
authors.initials: R
authors.lastname: Mülhaupt
authors.forename: Günter
authors.initials: G
authors.lastname: Reiter
mesh_terms: D003460:Crystallization; D018625:Microscopy, Atomic Force; D008970:Molecular Weight; D044367:Phase Transition; D020959:Polyethylene / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry*; D044366:Transition Temperature
chemical_list: D012996:Solutions; D020959:Polyethylene
keywords: annealing; atomic force microscopy (AFM); crystallization; microstructures; polyethylenes (PE)