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Title: Free Surface Relaxations of Star-Shaped Polymer Films

Here, the surface relaxation dynamics of supported star-shaped polymer thin films are shown to be slower than the bulk, persisting up to temperatures at least 50 degrees above the bulk glass transition temperature T$$bulk\atop{g}$$. This behavior, exhibited by star-shaped polystyrenes (SPSs) with functionality f = 8 arms and molecular weights per arm M arm < M e (M e is the entanglement molecular weight), is shown by molecular dynamics simulations to be associated with a preferential localization of these macromolecules at the free surface. This new phenomenon is in notable contrast to that of linear chain polymer thin film systems where the surface relaxations are enhanced in relation to the bulk; this enhancement persists only for a limited temperature range above the bulk T$$bulk\atop{g}$$. Finally, evidence of the slow surface dynamics, compared to the bulk, for temperatures well above T g and at length and time scales not associated with the glass transition has not previously been reported for polymers.
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7]
  1. Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, Crete (Greece)
  2. Univ. of Michigan, Ann Arbor, MI (United States). Department of Material Science and Engineering and Biointeraces Institute
  3. Univ. of Michigan, Ann Arbor, MI (United States). Biointeraces Institute and Macromolecular Science and Engineering
  4. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States). Materials Science and Engineering Division
  5. Argonne National Lab. (ANL), Argonne, IL (United States). X-ray Science Division
  6. National and Kapodistrian University of Athens (Greece). Department of Chemistry
  7. Univ. of Michigan, Ann Arbor, MI (United States). Department of Material Science and Engineering, Biointeraces Institute and Macromolecular Science and Engineering; National Renewable Energy Lab. (NREL), Golden, CO (United States)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 119; Journal Issue: 22; Journal ID: ISSN 0031-9007
American Physical Society (APS)
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1410474