title: Probing effective slippage on superhydrophobic stripes by atomic force microscopy.
abstract: While the effective slippage of water past superhydrophobic surfaces has been studied over a decade, theoretical predictions have never been properly confirmed by experiments. Here we measure a drag force on a sphere approaching a plane decorated by superhydrophobic grooves and compare the results with the predictions of semi-analytical theory developed here, which employs the gas cushion model to calculate the local slip length at the gas sectors. We demonstrate that at intermediate and large (compared to a texture period) separations the half-sum of longitudinal and transverse effective slip lengths can be deduced from the force-distance curve by using the known analytical theory of hydrodynamic interaction of a sphere with a homogeneous slipping plane. This half-sum is shown to depend on the fraction of gas sectors and its value is in excellent agreement with theoretical predictions. At small distances the half-sum of effective longitudinal and transverse slip lengths becomes separation-dependent, and is in quantitative agreement with the predictions of our semi-analytical theory.
authors.affiliation: A.N.Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31 Leninsky Prospect, 119071 Moscow, Russia. oivinograd@yahoo.com.
authors.forename: Tatiana V
authors.initials: TV
authors.lastname: Nizkaya
authors.affiliation: A.N.Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31 Leninsky Prospect, 119071 Moscow, Russia. oivinograd@yahoo.com and DWI - Leibniz Institute for Interactive Materials, RWTH Aachen, Forckenbeckstr. 50, 52056 Aachen, Germany.
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Dubov
authors.affiliation: DWI - Leibniz Institute for Interactive Materials, RWTH Aachen, Forckenbeckstr. 50, 52056 Aachen, Germany.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Mourran
authors.affiliation: A.N.Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31 Leninsky Prospect, 119071 Moscow, Russia. oivinograd@yahoo.com and DWI - Leibniz Institute for Interactive Materials, RWTH Aachen, Forckenbeckstr. 50, 52056 Aachen, Germany and Department of Physics, M.V.Lomonosov Moscow State University, 119991 Moscow, Russia.
authors.forename: Olga I
authors.initials: OI
authors.lastname: Vinogradova