Apparent depth-dependent modulus and hardness of polymers by nanoindentation: Investigation of surface detection error and pressure effects

Zhiyuan Qian, Jared Risan, Benjamin Stadnick, Gregory B. McKenna

Research output: Contribution to journalArticle

4 Scopus citations

Abstract

Nanoindentation is a widely used technique to characterize the mechanical properties of polymeric materials at the nanoscale. Extreme surface stiffening has been reported for soft polymers such as poly(dimethylsiloxane) (PDMS) rubber. Our recent work [J. Polym. Sci. Part B Polym. Phys. 2017, 55, 30–38] provided a quantitative model which demonstrates such extreme stiffening can be associated with experimental artifacts, for example, error in surface detection. In this work, we have further investigated the effect of surface detection error on the determination of mechanical properties by varying the sample modulus, instrument surface detection criterion, and probe geometry. We have examined materials having Young's moduli from ∼2 MPa (PDMS) to 3 GPa (polystyrene) using two different nanoindentation instruments (G200 and TI 950) which implement different surface detection methods. The results show that surface detection error can lead to apparent large stiffening. The errors are lower for the stiffer materials, but can still be significant if care is not taken to establish the range of the surface detection error in a particular experimental situation. We have also examined the effect of pressure beneath the probe on the nanoindentation-determined modulus of polystyrene with different probe geometries.

Original languageEnglish
Pages (from-to)414-428
Number of pages15
JournalJournal of Polymer Science, Part B: Polymer Physics
Volume56
Issue number5
DOIs
StatePublished - Mar 1 2018

Keywords

  • PDMS
  • depth-dependent properties
  • nanoindentation
  • poly(dimethyl siloxane)
  • polystyrene
  • polyurethane
  • pressure
  • surface detection

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