Adsorption trends with increasing salt concentration

With one exception (DPES—AOS on limestone), the anionic surfactants exhibit an increasing trend in adsorption with increasing salt concentration (Figure 13a), a result that is consistent with literature data. This result can be attributed to three effects surfactant solubility, surfactant-solid electrostatic interactions, and reduced electrostatic repulsion between surfactant head-groups in the adsorbed layer in the presence of excess counterions. 

Upon examining the adsorption data from the reservoir brines, there was no consistent pattern seen in the adsorption behavior. Based on this it was concluded that the tendency of surfactant adsorption to increase with increasing salt concentration is minor and that the trends in adsorption can be explained solely on the basis of the interaction of the charge on the surfactant with the solid surface charges. 

Finally, in fig. 3.55 T is given for a number of potassium salts, indicating increasing specific adsorption from KF (non-specific) to KBr. The plateau at negative potentials is lower than in fig. 3.54 because the electrolyte concentration is less. This figure may be compared with fig. 3.48, where similar lyotropic trends are found, and with fig. 3.40b, which is, apart from the different ordinate axis, the silver iodide counterpart. 

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