Equilibrium adsorption of surfactants

Keywords Equilibrium adsorption of surfactants Gas-liquid interface ... 

The lower imbibition rate in the gravity-dominated regime for a mixed-wet system compared to a water-wet system may be explained by adsorption of surfactant onto the chalk surface. The equilibrium adsorption of surfactant at concentrations above the CMC onto water-wet patches, in between patches with adsorbed organic matter from the oil, may create oil lenses. If oil lenses are formed and the oil pins to the surface, then brine imbibition would be drastically reduced. 

This section concerns the equilibrium adsorption of surfactants and kinetics of this process in aqueous systems. Flotation of SASs is based on this phenomenon. Equilibrium adsorption of surfactants at the air-water interface is described by Gibbs s theory, which shows the relationship between the surface excess of surfactants (SAS), surface tension of SAS solution, and its concentration. Many authors studied the adsorption phenomenon that occurs at the interfaces. Numerous mathematical models have been proposed. 

Similarly, the derivation of the Langmuir equation of gas adsorption allows us to consider the kinetics and the equilibrium adsorption of surfactants in the water-air system. In this system, the diffusion resistance layer controls the transfer of surfactant molecules from aqueous phase to its surface. The diffusion flux density J obeys Pick s equation, that is. 

And the dependence of equilibrium adsorption of surfactant vs. its volume concentration is calculated as... 

This quantity is a measure of the ratio of adsorption rate to rate of fluid convection through the system. The use of combinations of equations similar to Equations 7.30 and 7.34 to describe non-equilibrium flow behaviour is quite common whether its origin is in dead-end pore mass transfer (Coates and Smith, 1964) or in unsteady-state adsorption (Ramirez et a/., 1980 Van Geneuchten, 1981). Ramirez et al. (1980) have described non-equilibrium adsorption of surfactants in laboratory cores using this approach. 

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