Annealing and Recrystallization of Single Crystals of Polyethylene on Graphite: An Atomic Force Microscopy Study
- Citation data:
Journal of Macromolecular Science, Part B, ISSN: 0022-2348, Vol: 45, Issue: 2, Page: 169-194
- Publication Year:
- Repository URL:
- https://works.bepress.com/darrell_reneker/37; https://ideaexchange.uakron.edu/polymerscience_ideas/414
- Chemistry; Physics and Astronomy; Materials Science; high temperature AFM; single crystals of PE; lamellar thickening; epitaxial layer; recrystallization; melting; single polymer layers; Chemical Engineering; Engineering; Polymer Science
In situ and ex-situ atomic force microscopy (AFM) studies of annealing of solution-grown single crystals of polyethylene (PE) on graphite were performed at temperatures up to 170°C. Structural changes of the crystals began at ~90°C at the interface between the lamellar crystal and the substrate where solvent traces are likely trapped after crystal collapse. Initially, material at the edges and in a few central locations of the lozenge-shaped crystals was converted into 20 nm wide and 3 nm thick strands. As annealing temperature increases, this transformation spreads over the whole crystal, and at 110°C the arrays of the strands, which were oriented differently in the different crystal sectors, completely filled the lozenge frame. The final morphology, which reflects the recrystallization and most likely the reorientation of the PE chains from the vertical to the horizontal direction with respect to the substrate, does not depend on the sample drying prior to the annealing experiments. Annealing of the recrystallized PE samples led to flattening and widening of the strands, which transformed into stacks of molecular ribbons. Some of the ribbons extended from the lozenge shape to the substrate and their orientation results from epitaxy on the graphite. After melting of the polymer structures above 140°C, ordered molecular ribbons of partially extended polymer chains were detected at the melt-substrate interface at temperatures up to 170°C.