Hydrogen-bonded monolayers and interdigitated multilayers at the air-water interface

Stephen M. Martin, Kristian Kjaer, Markus J. Weygand, Isabelle Weissbuch, Michael D. Ward

Research output: Contribution to journalArticle

Abstract

Crystalline monolayers of octadecylsulfonate amphiphiles (C18S) separated by hydrophilic guanidinium (G) spacer molecules were formed at the air-water interface at a surface coverage that was consistent with that expected for a fully condensed monolayer self-assembled by hydrogen bonding between the G ions and the sulfonate groups. The surface pressure-area isotherms reflected reinforcement of this monolayer by hydrogen bonding between the G ions and the sulfonate groups, and grazing incidence X-ray diffraction (GIXD) measurements, performed in-situ at the air-water interface, revealed substantial tilt of the alkyl hydrophobes (t = 49° with respect to the surface normal), which allowed the close packing of the C18 chains needed for a stable crystalline monolayer. This property contrasts with behavior observed previously for monolayers of hexadecylbiphenylsulfonate (C16BPS) and G, which only formed crystallites upon compression, accompanied by ejection of the G ions from the air-water interface. Upon compression to higher surface pressures, GIXD revealed that the highly tilted (G)C18S monolayer crystallites transformed to a self-interdigitated (G)C18S crystalline multilayer accompanied by a new crystalline monolayer phase with slightly tilted alkyl chains and disordered sulfonate headgroups. This transformation was dependent on the rate of compression, suggesting kinetic limitations for the "zipper-like" transformation from the crystalline monolayer to the self-interdigitated (G)C18S crystalline multilayer.

Original languageEnglish (US)
Pages (from-to)14292-14299
Number of pages8
JournalJournal of Physical Chemistry B
Volume110
Issue number29
DOIs
StatePublished - Jul 27 2006

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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