Thermodynamics of Micelle Formation of the Counterion Coupled Gemini Surfactant Bis(4-(2-dodecyl)benzenesulfonate)-Jeffamine Salt and Its Dynamic Adsorption on Sandstone Annamária B. Páhi, † Zoltán Király,* ,† Ágnes Mastalir, ‡ József Dudás, § Sándor Puskás, | and Árpád Vágó | Department of Colloid Chemistry, UniVersity of Szeged, Aradi Vt. 1, H-6720 Szeged, Hungary, Department of Organic Chemistry, UniVersity of Szeged, Dóm tér 8, H-6720 Szeged, Hungary, Research Institute of Chemical and Process Engineering, UniVersity of Pannonia, Egyetem u. 10, H-8200 Veszprém, Hungary, and MOL Hungarian Oil and Gas Plc, E&P, New Technologies and R&D, P.O. Box 37, H-6701 Szeged, Hungary ReceiVed: July 23, 2008; ReVised Manuscript ReceiVed: September 24, 2008 A novel counterion-coupled gemini (cocogem) surfactant, DBSJ, was synthetized via the 2:1 coupling reaction between 4-(2-dodecyl)benzenesulfonic acid (Lutensit A-LBS) and polypropyleneglycol-bis(2-aminopropyl) ether (Jeffamine D230). The surfactant had a polydispersity index of M w /M n ) 1.04, as determined by electrospray-ionization mass spectrometry. The micellar properties of DBSJ in water were investigated in the temperature range 283-348 K by conductometry and titration microcalorimetry. The critical micelle concentration (cmc) of the cocogem was found to be more than 1 order of magnitude less than that of monomeric sodium 4-(2-dodecyl)benzenesulfonate (SDBS). The mean degree of dissociation in the temperature range studied proved to be R) 0.39. The calorimetric enthalpies of micelle formation agreed well with the enthalpies calculated via the van’t Hoff relation. The cmc versus T curve passes through a minimum just below room temperature, after which the micelle formation changes from endothermic to exothermic. The Gibbs free energy of micelle formation was nearly constant as the temperature was increased, due to enthalpy/ entropy compensation. The isotherm for DBSJ adsorption from aqueous solution onto sandstone was determined by continuous flow frontal analysis solid/liquid chromatography at 298 K and 60 bar. The adsorption of DBSJ on sandstone followed an S-type isotherm. Surface aggregation occurred over an extended range of concentration. Surface saturation was reached at a solution concentration more than 1 order of magnitude less than for monomeric SDBS. This finding is a point of concern in the chemical flooding of oil reservoir rocks to enhance oil recovery. Introduction Gemini (dimeric) surfactants are composed of two am- phiphilic moieties having the structure of conventional (mon- omeric) surfactants connected by a spacer group close to the head groups. 1-3 To date, various kinds of gemini surfactants have been synthetized (anionic, cationic, zwitterionic, and nonionic) with a large variety of spacer groups (hydrophilic or hydrophobic, short or long, rigid or flexible). Because of their highly effective performance, gemini surfactants are of potential use in the chemical industry for the production of pharmaceu- ticals, cosmetics, household materials, medical science and agricultural chemicals, and in enhanced oil recovery (EOR). 1-3 Gemini surfactants possess advantages which are superior to those of their single-chain counterparts, including greater interfacial activities and much lower critical micelle concentra- tions (cmcs). For hydrophilic spacers, the cmc increases slightly with progressive spacer length. 4,5 For hydrophobic spacers, the cmc passes through a weak maximum with increasing spacer length. 6-9 For a given spacer, the cmc decreases with increase in the length of the alkyl chains. 10,11 Calorimetric studies have indicated that micelle formation becomes more exothermic with increasing alkyl chain length 11 and rising temperature. 7,9 The enthalpy of micellization displays a minimum with increase of the spacer length. 4,8,9 The adsorption of cationic gemini surfactants from water onto hydrophilic silica and silicate surfaces has been extensively studied. 12-17 The initial, direct adsorption of the organic cations onto the negatively charged surface is followed by the formation of surface aggregates via a co-operative adsorption mechanism until surface saturation is reached close to the cmc. The maximum surface coverage decreases with increasing spacer length. AFM studies have indicated the formation of bilayers, spherical, or cylindrical surface aggregates, depending on the surface charge density of the underlying substrate. 17,18 The surface micelles become more flattened as the spacer length of the amphiphile increases. Little attention has been paid so far to the adsorption of anionic gemini surfactants at solid/solution interfaces. It has been reported that the amount of disodium didecyldiphenyl ether disulfonate adsorbed on limestone is about half-that of mono- sodium monodecyldiphenyl ether monosulfonate. 15 The extents of adsorption of both the monomeric and the dimeric derivatives from aqueous solution onto sand have been found to be negligible. 15 However, conventional anionic surfactants, such as sodium alkylbenzene sulfonates, display appreciable adsorp- * To whom correspondence should be addressed. E-mail: zkiraly@ chem.u-szeged.hu. † Department of Colloid Chemistry, University of Szeged. ‡ Department of Organic Chemistry, University of Szeged. § University of Pannonia. | MOL Hungarian Oil and Gas Plc. J. Phys. Chem. B 2008, 112, 15320–15326 15320 10.1021/jp806522h CCC: $40.75  2008 American Chemical Society Published on Web 11/07/2008