Surface active and thermodynamic properties of some surfactants derived from locally linear and heavy alkyl benzene in relation to corrosion inhibition efficiency A. M. Al-Sabagh, H. M. Abd-El-Bary, R. A. El-Ghazawy, M. R. Mishrif * and B. M. Hussein Linear and heavy alkyl benzene (HAB) were sulfonated with fuming sulfuric acid (oleum) and the sulfonated products were esterified with tri and poly ethanolamine (d ¼ 4 and 6). The prepared three esters from each series were quaternized with n-butyl bromide. The resulted six quaternized ester of linear and HAB sulfonate were named as (L1Q, L2Q, L3Q, H1Q, H2Q, and H3Q). The surface and thermodynamic properties of these compounds have been investigated. From the data obtained, it was found that surface tension and surface active properties for the HAB derivatives were better than which obtained from linear alkyl benzene (LAB) derivatives. From the results obtained from the surface activity, the best performance compound from each group was selected to study the corrosion inhibition efficiency of them relative to the surface activity. The obtained results show that the LAB derivative L3Q exhibited inhibition efficiency (93.1%) at 1000 ppm but H3Q exhibited (97%) at 600 ppm. The diversity of the resulted data obtained was discussed in the light of chemical structure of the alkyl benzene sulfonate. 1 Introduction Surfactants were widely used and find a very large number of applications because of their remarkable ability to influence the properties of surfaces and interfaces. Corrosion was among the important applications of surfactants especially in the petroleum industry [1–6]. There are generally two approaches for treating surfactant adsorption at the air/liquid and liquid/liquid interfaces. The first approach, adapted by Gibbs, treats adsorption as an equilibrium phenomenon whereby the second law of thermodynamics may be applied using surface quantities. The second approach, called the equation of state approach, treats the surfactant film as a two- dimensional layer with a surface pressure that may be related to the surface excess (amount of surfactant adsorbed per unit area). The thermodynamic parameter of standard free energy change of adsorption and micellization is one of the most important characteristics of surfactant solution and hence it is essential to understand its mechanism (the driving force for micelle formation) [7–13]. Although corrosion was inevitable, it can be controlled by several techniques. These methods can be divided into thermo- dynamic protection, kinetic protection, barrier protection, structure design, environmental control, and metallurgical design. The use of corrosion inhibitors was one of the most practical methods for protecting internal walls of pipelines. The inhibitors were chemical substances that were added to a liquid (usually water) to prevent corrosion or to control it at an acceptable low corrosion rate. Surfactants were selected for their effectiveness in protecting the specific metal or combination of metals in a given system. The corrosion inhibition of a metal involves strong adsorption of the inhibitors to the metal surface through their functional groups as phosphorus, oxygen, nitrogen, sulfur, double bond, or phenyl ring [14, 15]. In this article, synthesis and evaluation of some surface properties of surfactants derived from heavy alkyl benzene (HAB) and linear alkyl benzene (LAB) was the main object. The effect of the hydrophilic head length and the hydrophobic tail on surface active properties were investigated. Our attention should be extended to get relation between surface active properties and corrosion inhibition ability of some selected surfactants. Materials and Corrosion 2011, 62, No. 11 DOI: 10.1002/maco.201006017 1015 A. M. Al-Sabagh, R. A. El-Ghazawy, M. R. Mishrif Egyptian Petroleum Research Institute (EPRI), Nasr City, Cairo (Egypt) E-mail: csde.epri@yahoo.com H. M. Abd-El-Bary Faculty of Science, Al-Azhar University, Nasr City, Cairo (Egypt) B. M. Hussein E-Gas Company, Nasr City, Cairo (Egypt) www.matcorr.com wileyonlinelibrary.com ß 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim