Brush-sheathed particles diffusing at brush-coated surfaces in the thermally responsive PNIPAAm system

Huilin Tu, Liang Hong, Stephen M. Anthony, Paul V. Braun, Steve Granick

Research output: Contribution to journalArticle

Abstract

Phase-contrast microscopy and particle tracking algorithms are used to study the near-surface diffusion of poly-(N-isopropylacrylamide) (PNIPAAm) brush functionalized micron-sized silica microspheres after sedimentation from aqueous suspension onto planar substrates coated with a similar polymer brush above and below the lower critical solution temperature (LCST) of PNIPAAm, 32°C. A small negative charge on the wall and the particles (ζ potential = -6 mV) prevents adhesion above and below the LCST. The near-surface translational diffusion coefficient (Dsurface) is compared to the bulk-phase translational diffusion coefficient (Dbulk), which was measured by dynamic light scattering. We find that Dsurface/D bulk ≈ 0.6 at temperatures T < 32°C but rises abruptly to ∼0.8-0.9 at T > 32°C. Near-surface diffusion is expected to be slower than bulk diffusion owing to hydrodynamic coupling to the wall, implying reduced hydrodynamic coupling at the higher temperatures, perhaps mediated by enhanced electrostatic repulsion above the LCST transition.

Original languageEnglish (US)
Pages (from-to)2322-2325
Number of pages4
JournalLangmuir
Volume23
Issue number5
DOIs
StatePublished - Feb 27 2007

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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