title: Adsorption of cationic monomeric and gemini surfactants on montmorillonite and adsolubilization of vitamin E.
abstract: Adsorption of a cationic gemini surfactant (1,2-bis(dodecyldimethylammonio) ethane dibromide, 12-2-12) and the corresponding monomeric surfactant (dodecyltrimethylammonium bromide, DTAB) on montmorillonite has been characterized with a combination of adsorption isotherm, interlayer spacing and FT-IR spectroscopic data. Adsolubilization of vitamin E into the adsorbed surfactant layers has also been studied. The adsorption isotherm data reveal that the adsorption of the two surfactants is driven by the two factors: one is the cation exchange that occurs on the interlayer basal planes and the other is the hydrophobic interaction between hydrocarbon chains of the surfactants. Although the adsorbed amount measured in the saturation region (in mol g(-1)) is almost identical for the two surfactants, the conformation of the intercalated surfactant molecules differs significantly from each other. The adsorption of DTAB results in a lateral bilayer arrangement in the limited interlayer space, whereas 12-2-12 gives a normal bilayer arrangement in the expanded interlayer space. Adsolubilization of vitamin E takes place into the adsorbed surfactant layers, and interestingly, all the vitamin E molecules added in the montmorillonite suspensions are hybridized at lower surfactant concentrations due to the great specific surface area of the clay material. Since the maximum adsolubilization amount is usually obtained just below the critical micelle concentration, the gemini surfactant is deemed to be more efficient than the corresponding monomeric one to achieve the great adsolubilization amount.
authors.affiliation: Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, Noda, Chiba, Japan. k-sakai@rs.noda.tus.ac.jp <k-sakai@rs.noda.tus.ac.jp>
authors.forename: Kenichi
authors.initials: K
authors.lastname: Sakai
authors.forename: Erimi
authors.initials: E
authors.lastname: Nakajima
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Takamatsu
authors.forename: Suraj C
authors.initials: SC
authors.lastname: Sharma
authors.forename: Kanjiro
authors.initials: K
authors.lastname: Torigoe
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Yoshimura
authors.forename: Kunio
authors.initials: K
authors.lastname: Esumi
authors.forename: Hideki
authors.initials: H
authors.lastname: Sakai
authors.forename: Masahiko
authors.initials: M
authors.lastname: Abe
mesh_terms: D000327:Adsorption; D001546:Bentonite / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D008823:Micelles; D010316:Particle Size; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012995:Solubility; D017550:Spectroscopy, Fourier Transform Infrared; D013501:Surface-Active Agents / Q000737:chemistry*; D013816:Thermodynamics; D024505:Tocopherols / Q000737:chemistry*
chemical_list: D002412:Cations; D008823:Micelles; D000644:Quaternary Ammonium Compounds; D013501:Surface-Active Agents; D001546:Bentonite; C013912:decyltrimethylammonium; C022806:dodecyltrimethylammonium; D024505:Tocopherols