AFM study of hydrodynamics in boundary layers around micro- and nanofibers

TL;DR

This study uses advanced atomic force microscopy techniques to quantitatively analyze hydrodynamic interactions around micro- and nanofibers, validating a theoretical model and enabling nanoscale fluid dissipation investigations.

Contribution

It introduces a combined AFM approach to measure hydrodynamic forces at the nanoscale and validates a model relating friction to the probe size and boundary layer thickness.

Findings

Experimental data collapse onto a master curve

Friction depends on the ratio of probe radius to boundary layer thickness

Model accurately predicts hydrodynamic forces at nanoscales

Abstract

The description of hydrodynamic interactions between a particle and the surrounding liquid, down to the nanometer scale, is of primary importance since confined liquids are ubiquitous in many natural and technological situations. In this paper, we combine three non-conventional atomic force microscopes to study hydrodynamics around micro- and nano-cylinders. These complementary methods allow the independent measurement of the added mass and friction terms over a large range of probe sizes, fluid viscosities and solicitation conditions. A theoretical model based on an analytical description of the velocity field around the probe shows that the friction force depends on a unique parameter, the ratio of the probe radius to the thickness of the viscous boundary layer. We demonstrate that the whole range of experimental data can be gathered in a master curve which is well reproduced by the model. This validates the use of these AFM modes for a quantitative study of nano-hydrodynamics, and opens the way to the investigation of other sources of dissipation in simple and complex fluids down to the nanometer scale.