Quantifying effective slip length over micropatterned hydrophobic surfaces

TL;DR

This study uses micro-PIV to measure slip lengths in hydrophobic microchannels with micro-grooves, revealing how groove width and meniscus curvature influence slip behavior, with results differing from idealized models.

Contribution

It provides experimental insights into how micro-groove width and meniscus curvature affect slip length in hydrophobic microchannels, highlighting deviations from theoretical predictions.

Findings

Slip length increases with wider micro-grooves

Measured slip length is smaller than theoretical predictions

Meniscus curvature significantly impacts slip behavior

Abstract

We employ micro-particle image velocimetry ($\mu$-PIV) to investigate laminar micro-flows in hydrophobic microstructured channels, in particular the slip length. These microchannels consist of longitudinal micro-grooves, which can trap air and prompt a shear-free boundary condition and thus slippage enhancement. Our measurements reveal an increase of the slip length when the width of the micro-grooves is enlarged. The result of the slip length is smaller than the analytical prediction by Philip et al. [1] for an infinitely large and textured channel comprised of alternating shear-free and no-slip boundary conditions. The smaller slip length (as compared to the prediction) can be attributed to the confinement of the microchannel and the bending of the meniscus (liquid-gas interface). Our experimental studies suggest that the curvature of the meniscus plays an important role in microflows over hydrophobic micro-ridges.