| 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 fromaqueous suspension onto planar substrates coated with a similar polymer brush above and below the lower criticalsolution 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/Dbulk ≈ 0.6 at temperatures T< 32 °C but rises abruptly to ∼0.8−0.9 at T> 32 °C. Near-surfacediffusion is expected to be slower than bulk diffusion owing to hydrodynamic coupling to the wall, implying reducedhydrodynamic coupling at the higher temperatures, perhaps mediated by enhanced electrostatic repulsion above theLCST transition.
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