Yoshifumi Koide

Interactions of poly(amidoamine)dendrimers having surface carboxyl groups with cationic surfactants

Abstract Interactions between poly(amidoamine)dendrimers with surface carboxyl groups and cationic surfactants in aqueous solutions were investigated by surface tension, fluorescence spectra, and dynamic scattering measurements. The dendrimers used were three generations (G1.5, 3.5, and 5.5) and two cationic surfactants were dodecyltrimethylammonium bromide (DTAB) and 1,2-bis(dodecyldimethylammonio)ethane dibromide (2RenQ). Under a constant concentration of surface groups of the dendrimers, the results of surface tension and fluorescence spectra measurements indicate that aggregates between DTAB and the dendrimers are formed at lower DTAB concentration than that of DTAB alone, whereas those between 2RenQ and the dendrimers are formed at higher 2RenQ concentration than that of 2RenQ alone. In addition, the aggregates show higher surface activity when the generation decreases from 5.5 to 1.5. Hydrodynamic radius obtained from dynamic scattering measurement suggests that the aggregates are formed by adsorbing surfactant on the surface of the dendrimers, not by bridging the dendrimers through the surfactant.

Preparation of gold nanoparticles using 2-vinylpyridine telomers possessing multi-hydrocarbon chains as stabilizer

Abstract Gold nanoparticles have been prepared in water by reduction of HAuCl 4 with NaBH 4 in the presence of 2-vinylpyridine telomers. The telomers ( n R m -2VPQ, n is the total number of chain; m is the main chain length) consist of multi-octyl side chains or multi-dodecyl side chains (2.1R 8 -2VPQ, 2.5R 12 -2VPQ, and 3.4R 12 -2VPQ). The particle size of gold decreases with increasing telomer concentration and stable gold nanoparticles are obtained above the critical micelle concentration of the telomer. The change in the particle size can be correlated with the structure of the telomer; when the alkyl chain length is longer and the total chain number is greater, the size becomes smaller.

Competitive adsorption of cationic surfactant and pesticide on laponite

Abstract Simultaneous adsorption of quaternary ammonium surfactants (mono-, di- and tri-) and 1,1′-dimethyl-4,4′-bipyridinium dichloride (paraquat) on laponite was studied under a constant feed concentration of paraquat where an amount adsorbed of paraquat in the absence of surfactants corresponded to about 10% of cationic exchange capacity of the laponite. The adsorbed amount of paraquat decreased with increasing adsorbed amount of the surfactant, indicating a competitive adsorption between paraquat and the surfactant. In addition, the replacement of paraquat with the adsorption of cationic surfactant was very similar for the three surfactants. The interlayer space with the adsorption of paraquat increased with increasing adsorbed amount of the surfactant.

The effect of added salt on adsorption and adsolubilization by a gemini surfactant on silica

Abstract Adsorption of a dimeric (1,2-bis(dodecyldimethylammonio) ethane dibromide, 2RenQ) on silica from its aqueous solution has been investigated in presence of added NaBr. The adsorbed amounts of 2RenQ at saturation increase with increasing amount of NaBr added. The dispersion stability of silica suspensions caused by adsorption of 2RenQ is well correlated with the change in ξ potentials. With a constant feed concentration of 2-naphthol, the adsolubilized amounts of 2-naphthol are greater when NaBr is added, but the ratios of adsolubilized amount of 2-naphthol/adsorbed amount of 2RenQ at maximum adsolubilization decrease with increasing NaBr concentration. This result is interpreted by the change in microviscosity of the 2RenQ adsorbed layer, as estimated by the ESR probe technique. In addition, from a two-step process of adsorption-adsolubilization, it is found that 2RenQ adsorbs on silica much more strongly in presence of added NaBr, keeping 2-naphthol in the adsorbed layers, than when NaBr is not added.

Sorption of 2-naphthol and copper ions by cationic surfactant-adsorbed laponite

Abstract As one of applications of adsolubilization, a simultaneous sorption of 2-naphthol and copper ions by cationic surfactant-adsorbed laponite was carried out. Both the surfactant-adsorbed laponite using dodecyl trimethylammonium bromide (DTAB) and 1,2-bis(dodecyldimethylammonio) ethane dibromide (2RenQ) retained a high sorption capacity for copper ions, while the 2RenQ-adsorbed laponite completely adsolubilized 2-naphthol in a whole concentration region, but the DTAB-adsorbed laponite one decreased the adsolubilization gradually above the cmc of DTAB. Thus, it was found that laponite having cationic surfactant-adsorbed layer has a great capacity for a simultaneous removal of both toxic nonionic and ionic compounds.

Physicochemical properties of resorcinol-type calix[4]arenes phosphoric esters having four alkyl side chains in aqueous solution

The physicochemical properties of phosphate esters of resorcinol-type of calix[4]arenes([4]Ar5P-Rn; side chain length n=6, 8, and 12) in aqueous solutions have been characterized by several techniques including surface tension and NMR. It is found that the critical micelle concentrations (cmcs) of [4]Ar5P-Rn are insensitive against the alkyl side chain length, whereas the polarity of aggregates remarkably depends on the alkyl side chain length. From static light scattering and NMR measurements it is suggested that the shapes of aggregates of [4]Ar5P-Rn are not globular and the alkyl side chains of [4]Ar5P-Rn gather loosely in the aggregates. The mixed properties of [4[Ar5P-R12 and hexaethyleneglycol dodecylether have also been investigated. The mixed cmcs are considerably greater than those of the respective surfactant cmcs and the interaction parameter calculated using a modified regular solution theory is +2.7. These results indicate that the repulsive interactions occur in the mixed micelles.

Studies of collectors. Part 12. The flotation of gallium ion with polyphenol-type surfactants

Polyphenol-type surfactants bearing 1,2-benzenediol or 1,2,3-trihydroxybenzene units were prepared and applied as flotation collectors for Ga3+. The surfactants exhibited a lowering of surface tension at pH 11 (32–47 dyn cm–1. Gallium(III) was highly floated (80–90%) at pH 3–8 with equimolar Cn– 1H2n– 1C(O)C6H3(OH)2(n= 8 or 12) or C7H15C(O)C6H2(OH)3, but not as highly (60%) with C12H25S[CH2CHC(O)C6H3(OH)2]4.8(CH2CHCO2H)9.5H. The floatabilities of Ga3+ in 1 mol dm–3 NaOH were 86–99%, those in 3 mol dm–3 NaOH were 63–67%, and those in 5 mol dm–3 NaOH were 26–39% by using a six-fold molar excess of Cn– 1H2n– 1C(O)C6H3(OH)2(n= 12 or 18). On the other hand, the floatabilities from 1–5 mol dm–3 NaOH solutions when Cn– 1H2n– 1C(O)C6H2(OH)3 was added were nearly constant (58–59% with n= 12 and 31–35% with n= 18). The Ga3+ in a Ga3+–Al3+ mixture was floated selectively at pH 3–5 by using C7H15C(O)C6H3(OH)2 or C7H15C(O)C6H2(OH)3. Moreover, the polyphenol-type surfactants in these flotation systems were almost entirely absent (<10–5 mol dm–3) from 3–5 mol dm–3 NaOH solutions and little decomposed.