Interface characteristics of polystyrene melts in free-standing thin films and on graphite surface from molecular dynamics simulations

POLYMER

卷:116

Article

Lee, Sanghun^1,2  Lyulin, Alexey V.³  Frank, Curtis W.⁴  Yoon, Do Y.^2,4 

[1] Gachon Univ, Dept Nanochem, Seongnam 13120, Gyunggido, South Korea

[2] Seoul Natl Univ, Dept Chem, Seoul 08826, South Korea

[3] Tech Univ Eindhoven, Dept Appl Phys, Theory Polymers & Soft Matter Grp, NL-5600 MB Eindhoven, Netherlands

[4] Stanford Univ, Dept Chem Engn, Stanford, CA 94305 USA

关键词: Polystyrene films;    Free-standing films;    Polymer-graphite interface;    Segment density profile;    Phenyl distribution;    Phenyl orientation;    Chain orientation;    Thin film Tg;   

DOI  :  10.1016/j.polymer.2017.02.078

来源: Elsevier

【 摘 要 】

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.

【 授权许可】

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