Clay stabilization, surfactant adsorption

Surfactants may not only stabilize system against coagulation, but may have an opposite effect, i.e. cause destabilization in cases when the surfactant adsorption proceeds against the polarity equalization rule (Chapter III,2), e.g., during chemisorption of surfactants from aqueous medium on a hydrophilic surface. For example, small additives of cationic surfactants cause coagulation of aqueous dispersions of clays and other silicates due to hydrophobization at T< rmax. Further increase in surfactant concentration results in the formation of a second (hydrophilizing) adsorption layer and leads to an increased... 

Cationic surfactants adsorb strongly on clay surfaces by cation exchange. The fatty tails of these adsorbed surfactants impart oil-wetness to the clay surfaces and shield the clays from direct contact with water. This shielding has an obvious stabilizing effect however, this change in wettability often results in undesirable side effects, such as a decrease in oil relative permeability. Moreover, because of the possibility of multilayered adsorption (formation of surface micelles), a high surfactant concentration is required to satisfy the cation exchange capacity of the clays, which can make such treatments rather expensive. 

The synthesis of palladium nanoparticles on montmorillonite layer silicates was studied. The Pd particles were prepared in situ in the interlamellar space of montmorillonite dispersed in an aqueous medium. Macromolecules were adsorbed on the support from an aqueous solution, followed by adsorption and reduction of Pd ions. The Pd° nanoparticles appear and grow in the internal, interlamellar space as well as on the external surfaces of the lamellae. Well-crystallized kaolinite clay can be disaggregated by the intercalation of DMSO to individual lamellae, which may serve as excellent supports for metal nanoparticles. After the adsorption of palladium precursor, metal nanocrystals were reduced by hydrazine or sodium borohydride between the kaolinite lamellae, i.e., in the interfacial layer acting as a nanoreactor. The incorporation of nanoparticles between the lamellae was shown hy XRD measinements. This procedure makes possible the steric control and restriction of nanoparticle growth. The stability of nanoparticles can be further enhanced hy the addition of polymers (PVP) and surfactants (alkyl-ammonium salts) that are also adsorbed between the kaolinite lamellae. The presence of the particles was also verified and their sizes were quantified by TEM measurements. 

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