Mechanical anisotropy of nanostructured parylene films during sliding contact

Eric So, Melik C. Demirel, Kathryn J. Wahl

Research output: Contribution to journalArticle

25 Scopus citations

Abstract

Microscale sliding friction experiments were performed on nanostructured poly-chloro-p-xylylene (PPX-Cl, a.k.a, parylene) films. Oblique-angle vapour-phase deposition resulted in nanostructured columnar films tilted 57°-63° relative to the surface. The mechanical response to sliding was studied relative to the film structural anisotropy by examining contact friction and deformation in three sliding orientations: 'with', 'against' and 'perpendicular' to the tilt axis of the columns. Friction coefficients were uniformly high (0.5-1.5) for all orientations. Neither frictional anisotropy nor depth hysteresis was observed for sliding perpendicular to the column tilt axis. However, sliding 'with' and 'against' the column tilt axis resulted in measurable friction anisotropy as well as depth hysteresis, with larger contact depths and higher friction coefficients for sliding 'with' the column tilt. In comparison, planar films did not exhibit either frictional anisotropy or depth hysteresis. The depth hysteresis during sliding parallel to the tilt axis is attributed to the lateral force contribution to the total contact loading. Contacts formed when the sliding orientation was perpendicular to the column tilt axis were nominally Hertzian, allowing estimation of elastic moduli of the films from the load-displacement data during sliding. These films may have applications in the area of tissue engineering for directional cell sheet growth, MEMS developments for directional microfluidic pumps and sensors for deformation induced detection.

Original languageEnglish (US)
Article number045403
JournalJournal of Physics D: Applied Physics
Volume43
Issue number4
DOIs
StatePublished - Feb 22 2010

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Acoustics and Ultrasonics
  • Surfaces, Coatings and Films

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