Effect of electrolyte on interfacial dilational properties of chemical flooding systems by relaxation measurements

In the present work, the influences of different types of electrolytes on interfacial dilational properties of anionic surfactant sodium 4,5-diheptyl-2-propylbenzene sulfonate 377 and asymmetrical anionic Gemini surfactant C12COONa-p-C9SO3Na in the absence or presence of 1500 ppm partly hydrolyzed polyacrylamide were studied at decane-water interface, respectively, by means of interfacial tension relaxation measurements. The decay curves of interfacial tension were fitted by the summation of a number of exponential functions. The dilational elasticity (epsilon(r)) and dilational viscosity component (epsilon(i)) were calculated by Fourier transform and displayed as Cole-Cole plots (plotting epsilon(i) or epsilon(i)/epsilon(0) as a function of epsilon(r) or epsilon(r)/epsilon(0) respectively). The experimental results show that only single reorientation process dominates the interfacial properties in the presence of any electrolyte for 1 x 10(-6) mol L-1 377 solution, resulting form the more compacted film by electrostatic screening. On the other hand, the contribution of reorientation process at higher frequency decrease after the addition of NaCl and there exists no pure reorientation process in the presence of CaCl2 or MgCl2 for Gemini surfactant because of the slight increase of interfacial concentration due to larger molecular size and strong steric hindrance between alkyl chains. The addition of polymer can significantly modify the dilational properties of adsorbed surfactant layer due to the formation of mixed adsorption film through hydrophobic interaction between polymer chain and alkyl chain of surfactant molecule. The normalized Cole-Cole plots of surfactant-polymer films with different types of electrolytes show the similar characteristic in general and no pure reorientation process can be observed in any case. (C) 2011 Elsevier Ltd. All rights reserved.