Chain-Length Anomaly in the Two-Dimensional Ordering of the Cationic Surfactants CnTAB at the Graphite/Water Interface, Revealed by Advanced Calorimetric Methods

Zoltán Király, Gerhard H. Findenegg, Ágnes Mastalir

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

Surfactants adsorbed at the graphite/aqueous solution interface form half-cylindrical surface micelles templated by a flat, ordered monolayer. Here, the differential heats of adsorption of even-numbered alkyltrimethylam-monium bromides CnTAB (n = 6-16) were measured in the monolayer region by frontal-flow calorimetry and pulsed-flow calorimetry. The monolayer self-assembles exothermically and with a negative change of heat capacity. Pure water and pure surfactant domains coexist in the submonolayer region. The differential heat of adsorption is independent of the surface coverage and increases linearly with n, but a step occurs between n = 10 and n = 12. The adsorption is reversible below this critical chain length, but is nonreversible above it. This anomaly has been interpreted in terms of a reorientation of the headgroup from nonbonding to bonding with respect to the surface, and the formation of two different two-dimensional crystal structures on the surface. Pulsed-flow calorimetry, ideally suited for the study of nonreversible adsorption processes, has a high potential for the investigation of a variety of solid/liquid interfacial phenomena that cannot be studied by other current calorimetric methods.

Original languageEnglish
Pages (from-to)12492-12496
Number of pages5
JournalJournal of Physical Chemistry B
Volume107
Issue number45
DOIs
Publication statusPublished - Nov 13 2003

ASJC Scopus subject areas

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

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