Probing the nanohydrodynamics at liquid-solid interfaces using thermal motion

TL;DR

This paper introduces a fluorescence correlation spectroscopy method to measure nanohydrodynamic properties at liquid-solid interfaces, achieving high resolution and confirming slip conditions on different surfaces.

Contribution

A novel optical technique using FCS to characterize nano-hydrodynamics at interfaces with nanometric resolution, confirming slip conditions and challenging the nano-bubble slippage hypothesis.

Findings

Confirms no-slip on wetting surfaces

Detects partial slip of 18 nm on non-wetting surfaces

Finds no evidence of nano-bubbles promoting slippage

Abstract

We report on a new method to characterize nano-hydrodynamic properties at the liquid/solid interface relying solely on the measurement of the thermal motion of confined colloids. Using Fluorescence Correlation Spectroscopy (FCS) to probe the diffusion of the colloidal tracers, this optical technique --equivalent in spirit to the microrheology technique used for bulk properties-- is able to achieve nanometric resolution on the slip length measurement. It confirms the no-slip boundary condition on wetting surfaces and shows a partial slip b=18 +/- 5 nm on non-wetting ones. Moreover, in the absence of external forcing, we do not find any evidence for large nano-bubble promoted slippage on moderately rough non-wetting surfaces.