Is there a thin film of air at the interface between water and smooth hydrophobic solids?

Min Mao, Jinhong Zhang, Roe Hoan Yoon, William A. Ducker

Research output: Contribution to journalArticle

69 Scopus citations

Abstract

Optical measurements using an ellipsometer are inconsistent with the existence of continuous air films that are greater than about 0.1 nm in thickness at the interface between water and silicon wafers that have been rendered hydrophobic through the adsorption of silane agents. If adsorbed air consists of discrete bubbles, then the separation between the bubbles must be much greater than the radius of a bubble. For example, an approximate calculation for 80 nm radius bubbles that are attached with the macroscopic contact angle shows that the minimum spacing consistent with our data is in the range of 5 μm to infinite separation, depending on the sample. Although these putative bubbles would be sparsely distributed, we cannot rule out a density that is great enough to affect surface force apparatus measurements. A new variant of the multiple incidence method for ellipsometry is described and used to decrease the error in determining the thickness of adsorbed films.

Original languageEnglish (US)
Pages (from-to)1843-1849
Number of pages7
JournalLangmuir
Volume20
Issue number5
DOIs
StatePublished - Mar 2 2004
Externally publishedYes

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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