Comment on ``Large Slip of Aqueous Liquid Flow over a Nanoengineered Superhydrophobic Surface'' by C-H Choi and C Kim

TL;DR

This paper critically examines previous claims of large slip lengths for water on nanoengineered superhydrophobic surfaces, highlighting experimental uncertainties and biases that challenge the validity of those claims.

Contribution

It provides an analysis of measurement uncertainties and biases, questioning the evidence for large slip lengths reported in prior work.

Findings

Experimental uncertainty ranges overlap with reported slip lengths.

Systematic bias affects measurements on superhydrophobic surfaces.

No conclusive evidence for large slip lengths can be drawn.

Abstract

In a recent Letter (Phys. Rev. Lett. vol 96, 066001 (2006), ref [1]), Choi and Kim reported slip lengths of a few tens of microns for water on nanoengineered superhydrophobic surfaces, on the basis of rheometry (cone-and-plate) measurements. We show that the experimental uncertainty in the experiment of Ref. [1], expressed in term of slip lengths, lies in the range 20 - 100 micrometers, which is precisely the order of magnitude of the reported slip lengths. Moreover we point out a systematic bias expected on the superhydrophobic surfaces. We thus infer that it is not possible to draw out any conclusion concerning the existence of huge slip lengths in the system studied by Choi and Kim.