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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

53 Scopus citations


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 (US)
Article number035431
JournalPhysical Review B - Condensed Matter and Materials Physics
Issue number3
StatePublished - Jul 17 2013

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics


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