Interface characteristics of polystyrene melts in free-standing thin films and on graphite surface from molecular dynamics simulations
- Authors
- Lee, Sanghun; Lyulin, Alexey V.; Frank, Curtis W.; Yoon, Do Y.
- Issue Date
- 5-May-2017
- Publisher
- ELSEVIER SCI LTD
- Keywords
- Polystyrene films; Free-standing films; Polymer-graphite interface; Segment density profile; Phenyl distribution; Phenyl orientation; Chain orientation; Thin film Tg
- Citation
- POLYMER, v.116, pp.540 - 548
- Journal Title
- POLYMER
- Volume
- 116
- Start Page
- 540
- End Page
- 548
- URI
- https://scholarworks.bwise.kr/gachon/handle/2020.sw.gachon/6110
- DOI
- 10.1016/j.polymer.2017.02.078
- ISSN
- 0032-3861
- Abstract
- Interface characteristics of polystyrene (PS) melts in free-standing thin films and on a graphite surface were investigated by molecular dynamics simulations employing an explicit all-atom force field. The calculated surface tension is in good agreement with experiment, which provides good support for the force field parameters employed. In the polymer/vacuum free-surface region, the density profile exhibits an enrichment of phenyl groups relative to the backbone alkyl groups at the outermost low-density free surface, but this free surface is followed by a layer of relatively depleted phenyls and enriched alkyls of ca. 7 angstrom thickness. In the free surface, the phenyl-ring normal vectors and backbone chain vectors are both preferentially oriented along the film surface, in agreement with available experiments. At the polymer/graphite interface, the backbone chain vectors are strongly oriented along the graphite surface whereas the orientation distribution of phenyl-ring normal vectors exhibits two maxima along the nearly parallel (20 degrees) and the perpendicular direction to the graphite-surface normal. A densely packed structure is formed at the PS-graphite interface, which strongly decreases the segmental chain mobility, in contrast to the enhanced segmental mobility in the free-surface region. (C) 2017 Elsevier Ltd. All rights reserved.
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