What x rays can tell us about the interfacial profile of water near hydrophobic surfaces

Ahmet Uysal, Miaoqi Chu, Benjamin Stripe, Amod Timalsina, Sudeshna Chattopadhyay, Christian M. Schlepütz, Tobin J. Marks, Pulak Dutta

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40 Citations (Scopus)

Abstract

The free surface of water and the interface between water and a hydrophobic surface both have positive interface energies. The water density near a free surface drops below the bulk density, and thus it is expected that water near a hydrophobic surface will also show a density depletion. However, efforts by multiple groups to detect and characterize the predicted gap at water-hydrophobic interfaces have produced contradictory results. We have studied the interface between water and fluoroalkylsilane self-assembled monolayers using specular x-ray reflectivity and analyzed the parameter-space landscapes of the merit functions being minimized by data fitting. This analysis yields a better understanding of confidence intervals than the customary process of reporting a unique best fit. We conclude that there are unambiguous gaps at water-hydrophobic interfaces when the hydrophobic monolayer is more densely packed.

Original languageEnglish
Article number035431
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume88
Issue number3
DOIs
Publication statusPublished - Jul 17 2013

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ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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