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

Kiraly, Z.; Dekany, I.; Klumpp, E.; Schlimper, H.; Findenegg, G. H.

doi:10.1021/la001552y

Journal Article

PreJuSER-46882

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

Kiraly, Z. ; Findenegg, G. H. ; Klumpp, E.FZJ* ; Schlimper, H.FZJ* ; Dekany, I.

2001
ACS Publ. Washington, DC

Langmuir 17, 2420 - 2425 (2001) [10.1021/la001552y]

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Please use a persistent id in citations: http://hdl.handle.net/2128/801 doi:10.1021/la001552y

Abstract: 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.

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