Nanofluidics at hydrophilic and hydrophobic surfaces

MSc graduation project of Can Tümer
Location: Lab. for Aero & Hydrodynamics
Supervisors: M. Franken & C. Poelma
Start project: August 2010

Project description:

The development of microfluidics has raised new challenges to drive and manipulate flows in even more tiny channels. One key question concerns the nature of the boundary condition of fluids at solid surfaces, namely the no-slip boundary condition. Recent studies have demonstrated that hydrophobic surfaces develop hydrodynamic slippage at solid surfaces, as quantified by the so-called slip length. One technique that is capable of measuring near-wall flow velocities is nano-particle image velocimetry (nanoPIV). This technique uses an exponentially decaying evanescent wave, generated by Total Internal Reflection (TIR) and existing in the small volume (typically a few hundred nanometers) adjacent to the bottom surface of the channel, for the purpose of illuminating the fluorescent colloidal tracers. Using this approach makes it possible to determine two velocity components parallel to the wall averaged over the first few hundred nanometer next to wall along the optical axis. One of the properties of this evanescent wave, is that the illumination depth can be varied using the incident angle of the light. By calibrating the illumination depth of the evanescent wave, averaged flow velocities at different layers can be obtained.

The primary goal of this project is to determine slip lengths by measuring flow velocities very close to the surface (ranging from 100 to 500nm) at different layers using total internal reflection fluorescence microscopy (TIRFM) together with a statistical particle tracking velocimetry (SPTV) technique. Additionally the particle size and Electric Double Layer effects will be investigated for a broader understanding of the nanofluidic phenomena.

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