Disrupting Admicelle Formation and Preventing Surfactant Adsorption on Metal Oxide Surfaces Using Sacrificial Polyelectrolytes Javen S. Weston,* ,† Jeffrey H. Harwell, ‡,§ Benjamin J. Shiau, †,§ and Mahfuz Kabir † † Chemical, Biological and Materials Engineering; ‡ Department of Chemical Engineering; and § Petroleum Engineering, University of Oklahoma, Norman, Oklahoma 73019, United States ABSTRACT: The adsorption of anionic, cationic, and nonionic surfactants was measured on high-surface area silica and alumina nanoparticles when in the presence of the proposed polyelectrolyte sacrificial agents. Surfactant adsorption was characterized using two types of adsorption isotherms: one with constant polymer concentration and varying surfactant concentration, and another with a varying polymer concentration and constant surfactant concentration. Polystyrenesulfonate and Polydiallyl dimethylammonium chloride were tested as potential sacrificial agents on alumina and silica, respectively. Each surfactant/ polymer system was allowed to reach equilibrium and supernatant surfactant concentrations were measured. This information was then plotted in order to determine what, if any, effect the proposed sacrificial agent had on the equilibrium adsorption. Results indicate that both of these polymers can have a large effect on total surfactant adsorption at a variety of surfactant concentrations. ■ INTRODUCTION Surfactant adsorption on metal oxides is extremely important for a variety of practical applications from detergency 1 to enhanced oil recovery 2-4 and surfactant-aided environmental remediation. 5,6 In chemical flooding applications, a specially designed surfactant mixture is pumped into either the contaminated aquifer or oil reservoir to mobilize trapped oil by lowering the interfacial tension and, occasionally, changing the wettability of the rock formation or aquifer. Many variables can be changed in order to optimize the efficiency of the chemical flood, such as surfactant type, surfactant concentration, injection volume, pH, counterion valence and concentration, surfactant ratios (in multicompo- nent systems), and so forth. Surfactant adsorption onto soil or reservoir rock can impact many of these variables, most notably surfactant concentration and surfactant ratio, and have a negative effect on oil recovery. Surfactants lower interfacial tension by organizing themselves along the oil-water interface, therefore, any surfactant that is adsorbed on reservoir rock or aquifer soil cannot participate in lowering the interfacial tension and is not used to mobilize any hydrocarbon. Significant surfactant adsorption can greatly affect the economic viability of a chemical flood due to lower efficiency. Consequently, any method that can reduce the amount of surfactant adsorption during a chemical flood will result in a large increase in the number of viable applications for chemical flooding. Adsorption prevention is especially important because of surfactant molecules’ ability to form admicelles on solid surfaces. When surfactant concentrations are above the critical admicelle concentration (CAC), they deviate from the linear Henry’ s Law adsorption region where single surfactant molecules are adsorbing onto the surface with limited to no adsorbate-adsorbate interactions (Region “1” in Figure 1) and enter a period of cooperative adsorption where each adsorption site on a surface can adsorb multiple surfactant molecules (Region “2” in Figure 1) until the surface becomes a near- complete double-layer/admicelle slowing surfactant adsorption (Region “3” in Figure 1). The adsorbed double-layer is then slowly filled until a maximum adsorption plateau is reached (Region “4” in Figure 1). This nonlinear adsorption behavior is a major reason a sacrificial agent method is very attractive for preventing surfactant adsorption; it not only prevents the adsorption of the initial surfactant molecule, but could also aid Received: March 21, 2014 Revised: May 14, 2014 Published: May 14, 2014 Article pubs.acs.org/Langmuir © 2014 American Chemical Society 6384 dx.doi.org/10.1021/la501074x | Langmuir 2014, 30, 6384-6388