Adsorption calorimetric study of the organization of sodium n-decyl sulfate at the graphite/solution interface

Z. Király, G. H. Findenegg, E. Klumpp, H. Schlimper, I. Dékány

Research output: Article

36 Citations (Scopus)


The material and enthalpy balances of the adsorption of sodium n-decyl sulfate from aqueous solutions onto graphitized carbon black were determined between 288 and 318 K by using an automated flow sorption/microcalorimeter system. At low concentrations, the surfactant molecules form a flat monomolecular film on the graphite plane, in consequence of surface-directed ordering. A mechanism is proposed in which two adsorbed phases coexist during the formation of this surfactant monolayer. The enthalpy of adsorption in the monolayer region is ca. -42 kJ mol-1, which does not depend appreciably on the temperature or on the surface coverage. At higher concentrations, the ordered monolayer induces surface aggregation to produce half-cylindrical hemimicelles as the critical micelle concentration is approached. The enthalpies of surface aggregation at 288, 298, and 318 K are -10, -16, and -26 kJ mol-1, respectively. As the temperature is increased from 288 to 318 K, the average number of surfactant molecules in the cross section of a half-cylinder drops from ca. 5.4 to 3.4. Calorimetric evidence is provided that cationic and anionic surfactant adsorption on graphite follow the same mechanism in the low-density and high-density adsorbate regions.

Original languageEnglish
Pages (from-to)2420-2425
Number of pages6
Issue number8
Publication statusPublished - ápr. 17 2001

ASJC Scopus subject areas

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

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