Shear-dependent apparent slip on hydrophobic surfaces: The Mattress Model

TL;DR

This paper introduces a simple model explaining shear-dependent slip on hydrophobic surfaces by considering nanobubbles' dynamic response, aligning well with experimental observations of apparent slip.

Contribution

The model provides a mechanistic explanation for shear-dependent slip by incorporating nanobubble dynamics, a novel approach compared to previous theories.

Findings

Model predicts force decreases consistent with experiments

Nanobubbles cause apparent slip via a 'leaking mattress' effect

Shear-dependent slip explained by bubble compression and diffusion

Abstract

Recent experiments (Zhu & Granick (2001) Phys. Rev. Lett. 87 096105) have measured a large shear dependent fluid slip at partially wetting fluid-solid surfaces. We present a simple model for such slip, motivated by the recent observations of nanobubbles on hydrophobic surfaces. The model considers the dynamic response of bubbles to change in hydrodynamic pressure due to the oscillation of a solid surface. Both the compression and diffusion of gas in the bubbles decrease the force on the oscillating surface by a ``leaking mattress'' effect, thereby creating an apparent shear-dependent slip. With bubbles similar to those observed by atomic force microscopy to date, the model is found to lead to force decreases consistent with the experimental measurements of Zhu & Granick.