Wetting behavior of oppositely charged polystyrene sulfonate/hexadecyl trimethyl ammonium bromide complexes near critical aggregation concentration on carbonate reservoir rocks

Abstract

This paper reports on the wettability alteration of carbonate rocks from super-hydrophobic to super-hydrophilic in the presence of surfactant-polyelectrolyte complexes. In numerous industries such as oil recovery or paint technology, there is a recognized need for controlling the wettability of solid surfaces and particularly for producing super-hydrophobic or hydrophilic coatings. A growing body of evidence suggests that the surface activity of the Hexadecyl Trimethyl Ammonium Bromide (CTAB) will considerably increase in the presence of the oppositely charged Polystyrene Sulfonate (PSS) and form a surface-active multilayer complex in a range of concentrations from much lower than conventional surfactant critical micelle concentration (CMC) to CMC. The impact of adsorbing such a surface-active multilayer complex on the wetting behavior of CTAB-PSS solutions on solid surfaces, however, has scarcely been dealt with in the previous studies. This study sets out to determine the wetting behavior of CTAB-PSS mixtures on carbonate surfaces around the critical aggregation concentration, CAC, above which the multilayer surface structuring has been reported. Dynamic surface tension, dilational surface elastometry, and contact angle measurements were undertaken to first indicate the occurrence of multilayer structuring and second to explore the potential relationship between that and the wettability alteration of an oil-wet carbonate rock. The results are quite revealing, introducing an optimum CTAB concentration where surface elasticity and also the standard deviation of solution drop shapes from Laplacian profile are maximized and at the same time the contact angle is minimized. These values are 0.55 mM (for 50 ppm PSS) and 0.74 mM (for 20 ppm PSS), both quite lower than conventional CMC and above CAC. These findings are of crucial importance in coating science and in the manufacturing super-hydrophilic surfaces.