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ADSORPTION OF A C₁₀E₃ NON-IONIC SURFACTANT ON A Ca-SMECTITE

Institut des Sciences de la Terre d’Orléans, CNRS-Université d’Orléans, 1A Rue de la Ferollerie, 45071 Orléans Cedex 2, France

^* E-mail address of corresponding author: regis.guegan{at}univ-orleans.fr

The transformation of clay minerals into organo-clays by surfactant intercalation is of great environmental and industrial importance because it causes the clay to attract hydrophobic contaminants and other non-polar organic compounds, but a better understanding is needed of the mechanisms by which different classes of surfactants are intercalated. The purpose of this study was to synthesize and characterize an organo-clay comprising triethylene glycol monodecyl ether (C₁₀E₃) non-ionic surfactant, which has a lamellar phase at room temperature, intercalated into Ca-montmorillonite from Wyoming (SWy-2). The C₁₀E₃ non-ionic surfactant differed from previous non-ionic surfactants used in the formation of a lamellar phase in that it consisted of the stacking of molecules by hydrophobic interaction. C₁₀E₃-clay composites were characterized by complementary techniques (adsorption isotherms, X-ray diffraction, and infrared spectroscopy) and were compared to benzyldimethyltetradecyl ammonium chloride (BDTAC) cationic surfactant-clay composites for different loadings of the surfactant. For large loadings, the amount of C₁₀E₃ adsorbed, which can be described by the Langmuir equation, seemed to reach a steady state close to that of the cationic surfactant. The adsorption processes of the two surfactants were different. For the cationic surfactant, the adsorption, as described in the literature, was due to ion exchange between organic cations and Ca²⁺ counterions. The adsorption of C₁₀E₃ did not depend on electrostatic interaction but rather was due to several interaction mechanisms (H-bonding, ion-dipole, and hydrophobic interaction). For both surfactants, the expansion was limited to two adsorbed monolayers parallel to the clay surface. The expansion of the basal spacing to 17 Å suggested a complete dissociation of the C₁₀E₃ lamellar phase when adsorbed on the Ca-smectite. Organo-clays made using the non-ionic surfactant were stable, changing the chemical nature of clay to hydrophobic, and allowing for other cations to be exchanged, which has importance in the manufacture of new nanocomposites or geochemical barriers.

Key Words: Ca-smectite • Infrared Spectroscopy • Organo-clay • Surfactant • X-ray Diffraction