Near-surface mechanical properties of amorphous polymers

H.G.H. Melick, van, A. Dijken, van, J.M.J. Toonder, den, L.E. Govaert, H.E.H. Meijer

Research output: Contribution to journalArticleAcademicpeer-review

27 Citations (Scopus)

Abstract

Polymeric material near a free surface can have properties which deviate considerably from the bulk properties, Many researchers have reported a reduced glass transition temperature in thin polymeric films and attributed this effect to an enhanced segmental mobility near a free surface. It was also reported that sufficiently thin polymeric structures show a higher ductility than the bulk material. In this paper. we therefore investigate the hypothesis that the near-surface mechanical properties of amorphous polymers differ from the bulk properties owing to the presence of an absolute length scale. Microindentations and nanoindentations are performed on polystyrene, using a range of indenter sizes and indentation loads. In addition, numerical simulations are carried out with an advanced material model for polystyrene. A comparison between the experimental and numerical results indeed indicates that a length-scale effect is present near the surface. Simulations performed at an elevated temperature indicate that our results are consistent with the observations of a reduced T-g

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