Comment on ``Large Slip of Aqueous Liquid Flow over a Nanoengineered   Superhydrophobic Surface'' by C-H Choi and C Kim
  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. 
Lyderic Bocquet (Univ. Lyon I), Patrick Tabeling (EPSCI, Paris),   Sebastien Manneville (CRPP, Bordeaux)