Imidazolium-based zwitterionic surfactants: characterization of normal and reverse micelles and stabilization of nanoparticles.

This paper presents the physicochemical properties of micellar aggregates formed from a series of zwitterionic surfactants of the type 3-(1-alkyl-3-imidazolio)propane-sulfonate (ImS3-n), with n = 10, 12, 14, and 16. The ImS3-n dipolar ionic surfactants represent a versatile class of dipolar ionic compounds, which form normal and reverse micelles. Furthermore, they are able to stabilize nanoparticles in water and in organic media. Aqueous solubility is too low at room temperature to allow characterization of micellar aggregates but increases with addition of salts, allowing determination of aggregation number and cmc. As expected, these parameters depend on the length of the alkyl chain, and cmc values follow Klevens equation. In the presence of NaClO4, all ImS3-n micelles become anionoid by incorporating ClO4(-) on the micellar interface. A special feature of these surfactants is the ability to form reverse micelles and solubilize copious amounts of saline solutions in chloroform. (1)H NMR and infrared spectroscopic evidence showed that the maximum water to surfactant molar ratio w0 achievable depends on the concentration and type of salt dissolved. Reverse micelles of the ImS3-n surfactants can be used to stabilize metallic nanoparticles, whose size may be tuned by the amount of water dissolved.

Simultaneous nondestructive analysis of palladium, rhodium, platinum, and gold nanoparticles using energy dispersive X-ray fluorescence.

A selective method is proposed for the determination of palladium, gold, and sulfur in catalytic systems, by direct liquid analysis using energy dispersive X-ray fluorescence (EDXRF), under an atmosphere of helium or air. This method allows a nondestructive analysis of palladium, rhodium, platinum, and gold nanoparticulate catalysts stabilized by imidazolium propane sulfonate based zwitterionic surfactants, allowing the samples to be reused for catalytic studies. The signals from palladium, rhodium, platinum, and gold samples in the presence of imidazolium propane sulfonate-based zwitterionic surfactants obtained using EDXRF before (Pd(2+), Rh(2+), Pt(2+), and Au(3+)) and after (Pd(0), Rh(0), Pt(0), and Au(0)) formation of nanoparticles are essentially identical. The results show that the EDXRF method is nondestructive and allows detection and quantification of the main components of platinum, gold, rhodium, and palladium NPs, including the surfactant concentration, with detection and quantification limits in the range of 0.4-3 mg L(-1). The matrices used in such samples present no problems, even allowing the detection and quantification of interfering elements.

Imidazolium-based zwitterionic surfactant: a new amphiphilic Pd nanoparticle stabilizing agent.

Palladium nanoparticles (NPs) with an average size of 3.4 nm were prepared in water using imidazolium-based surfactant 3-(1-dodecyl-3-imidazolio)propanesulfonate (ImS3-12) as a stabilizer. The Pd NPs are highly dispersible in water and chloroform and were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy, powder X-ray diffraction, and dynamic light scattering. The results indicate that in water the NP surface is covered with a double layer of ImS3-12 molecules. The NPs were effective in the aqueous biphasic hydrogenation of cyclohexene, with easy recycling and no loss of catalytic activity after four successive runs.

Synthesis of a new zwitterionic surfactant containing an imidazolium ring. Evaluating the chameleon-like behavior of zwitterionic micelles.

Synthesis of a new zwitterionic surfactant containing the imidazolium ring 3-(1-tetradecyl-3-imidazolio)propanesulfonate (ImS3-14) is described. The solubility of ImS3-14 is very low but increases on addition of a salt which helps to stabilize the micellized surfactant. Fluorescence quenching and electrophoretic evidence for ImS3-14 shows that the micellar aggregation number is only slightly sensitive to added salts, as is the critical micelle concentration, but NaClO(4) markedly increases zeta potentials of ImS3-14 in a similar way as in N-tetradecyl-N,N-dimethylammonio-1-propanesulfonate (SB3-14) micelles. The rate of specific hydrogen ion catalyzed hydrolysis of 2-(p-heptoxyphenyl)-1,3-dioxolane and equilibrium protonation of 1-hydroxy-2-naphthoate ion in zwitterionic micelles of ImS3-14 and SB3-14 are increased markedly by NaClO(4) which induces anionoid character and uptake of H(3)O(+), but NaCl is much less effective in this respect. Comparison of ImS3-14 with SB3-14 is based on experimental evidence, and computational calculations indicate similarities and differences in structures of both compounds.