Force measurements between semifluorinated thiolate self-assembled monolayers: Long-range hydrophobic interactions and surface charge

T. Ederth, K. Tamada, P. M. Claesson, R. Valiokas, R. Colorado, M. Graupe, O. E. Shmakova, T. R. Lee

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)

Abstract

Long-range interactions between self-assembled monolayers (SAMs) of semifluorinated alkanethiols have been studied by direct force measurements in water and aqueous NaCl solutions. SAMs prepared from three different thiols, with identical fluorinated head groups but varying hydrocarbon spacer lengths, were investigated: CF3(CF2)9(CH2)xSH, where x = 2, 11, or 17. Force measurements show that the interactions in water and electrolyte solutions are composed of both double-layer interactions emerging from what appears to be charges adsorbed onto the surfaces and long-range "hydrophobic" attractions, in excess of the expected van der Waals forces. The three investigated thiols produce similar results in force measurements, though the contact angles with water are slightly different. The "hydrophobic" attraction has the form of step-like attractive discontinuities in the force profiles at separations ranging from 20 to 40 nm, caused by bridging of microscopic bubbles residing at the surfaces. The shape or range of these discontinuities are not significantly affected by replacement of the water with either 1 mM or 1 M NaCl solutions. The origin of the charges causing the electrostatic double-layer interaction is unclear, but some possible causes are discussed.

Original languageEnglish
Pages (from-to)391-397
Number of pages7
JournalJournal of Colloid And Interface Science
Volume235
Issue number2
DOIs
Publication statusPublished - Mar 15 2001
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Surfaces, Coatings and Films
  • Colloid and Surface Chemistry

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