Interfacial Phenomena and Colloid Stability: Basic Principles by Tadros Tharwat F

Author:Tadros, Tharwat F. [Tadros, Tharwat F.]
Language: eng
Format: epub
Publisher: De Gruyter
Published: 2015-05-04T16:00:00+00:00

8.6 Theoretical treatment of surfactant adsorption

Klimenko [17, 18] developed a theoretical model for the three stages of adsorption of nonionic surfactants. In the first stage (flat orientation) a modified Langmuir adsorption equation was used,

(8.18)

where c2 is the equilibrium concentration of surfactant in bulk solution, Γ2 is the surface excess concentration at C2 , is the surface excess at the cmc, Ka is a constant, a1 and are the effective cross-sectional areas of the solvent and adsorbate molecules in the surface, and is an adsorbate surface activity coefficient. The term in the square bracket is a type of surface “concentration” which is defined as the ratio of numbers of adsorbed surfactant molecules to the number of solvent molecules in the equilibrium interfacial layer. The constant Ka allows for adsorbate-adsorbent interactions and is therefore related to the energy of adsorption at infinite dilution. The adsorbate surface activity coefficient accounts for the adsorbate-adsorbate interaction and it is assumed to have the following dependence on Γ2 in the first stage of adsorption,

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