Thermo-osmotic flow in thin films

TL;DR

This study presents the first micro-scale measurements of thermo-osmotic flow in thin films, analyzing flow profiles and boundary effects on different surfaces using tracer nanoparticles.

Contribution

It provides experimental data on thermo-osmotic flow at the microscale and compares results with theoretical models, revealing complex boundary layer thermodynamics.

Findings

Thermo-osmotic coefficient for Pluronic F-127 matches Soret data.

Glass surface shows different thermo-osmotic behavior from literature.

Flow profiles agree with approximate analytical and numerical models.

Abstract

We report on the first micro-scale observation of the velocity field imposed by a non-uniform heat content along the solid/liquid boundary. We determine both radial and vertical velocity components of this thermo-osmotic flow field by tracking single tracer nanoparticles. The measured flow profiles are compared to an approximate analytical theory and to numerical calculations. From the measured slip velocity we deduce the thermo-osmotic coefficient for both bare glass and Pluronic F-127 covered surfaces. The value for Pluronic F-127 agrees well with Soret data for polyethylene glycol, whereas that for glass differs from literature values and indicates the complex boundary layer thermodynamics of glass-water interfaces.