Xiangtao Bai

C12mimBr ionic liquid/SDS vesicle formation and use as template for the synthesis of hollow silica spheres.

The phase behavior of an aqueous catanionic surfactant system, composed of a long-chain imidazolium ionic liquid 1-dodecyl-3-methylimidazolium bromide (C(12)mimBr) and sodium dodecyl sulfate (SDS), is described. The phase diagram of the catanionic system was determined by electrical conductivity measurements and the formation of vesicles in a birefringent L(alpha) phase characterized by transmission electron microscopy (TEM) and freeze-fracture transmission electron microscopy (FF-TEM). Rheological measurements were used to characterize the macroscopic properties of the birefringent L(alpha) phase. Both electrostatic and hydrophobic interactions contribute to the vesicle formation in the catanionic system. Compared to the DTAB/SDS aqueous solution, differences between the imidazolium and trimethylammonium headgroups geometric packing and charge density induce the different phase behavior in each system. Silica hollow spheres, with diameters 30-60 nm and a wall thickness of 8-10 nm, were prepared by using the vesicles as the templates. The hollow silica spheres were characterized by TEM, scanning electron microscopy (SEM), and nitrogen adsorption-desorption. The results suggest additional application for ionic liquid based vesicles to be used as templates for the synthesis of hollow inorganic materials.

Microstructures of Micellar Aggregations Formed within 1-Butyl-3-methylimidazolium Type Ionic Liquids

Nonionic surfactant Triton X-100 was shown to aggregate and form micellar aggregation in ionic liquids (ILs), 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)) and 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF(6)). The surface tension measurements revealed that the dissolution of Triton X-100 in ILs depressed the surface tension in a manner analogous to aqueous solutions, and a relatively higher critical micellar concentration (CMC) was obtained compared to that of water. Freeze-fracture transmission electron microscopy (FFTEM) shows that the micelles have an irregular droplet shape, which is larger than that formed in water. The micellar droplets preferred to assemble into larger clusters. (1)H NMR and two-dimensional rotating frame nuclear Overhauser effect (NOE) experiments (2D ROESY) show that the addition of Triton X-100 destroyed the ion pairs of pure ILs due to the electrostatic interaction between the positively charged imidazolium cation of ILs and the electronegative oxygen atoms of oxyethylene (OE) units of Triton X-100. The electrostatic interaction behaves similar to hydrogen bond that occurred between the OE units of nonionic surfactants and water molecules in aqueous micelles and cooperates with solvatophobicity, leading to the formation of IL micelles. The 2D ROESY analysis reveals that the microstructures of Triton X-100-based micelles in ILs are not regular spherical, which accords with the FFTEM image. Similar to the aqueous micellar systems, the hydrophobic interaction or solvatophobicity was found to drive the formation of micelles.

Siloxane surfactant induced self-assembly of gold nanoparticles and their application to SERS

A siloxane surfactant was used for the mild synthesis and simultaneous 1D assembly of gold nanoparticles. The length of the gold nanochains could be tuned by facile adjustment of the surfactant concentration. The multiple interactions between the siloxane surfactant and gold nanoparticles made the non-uniform spatial distribution of stabilizers at the nanoparticle surfaces and then led to the 1D assembly. Transmission electron microscopy (TEM) and UV-vis spectroscopy have been employed for characterizing the nanochains. The effect of ionic strength in the spontaneous linear assembly of gold nanoparticles was investigated to further elucidate the assembly of mechanism. These gold nanochains were shown to yield a large SERS enhancement for Rhodamine 6G.

Chiral ionic liquid monolayer-stabilized gold nanoparticles: synthesis, self-assembly, and application to SERS.

Chiral ionic liquid monolayer-stabilized gold nanoparticles were synthesized in a two-phase liquid-liquid system and found to self-assemble into ringlike structures at the air/water interface. Control experiments with long-chain ILs revealed that the molecular structure of the CIL significantly affects the formation of the gold nanoparticle ring structures. A possible mechanism based on Marangoni-Bénard convection in evaporating droplets was proposed. These gold nanoparticle structures were shown to yield a large SERS enhancement for Rhodamine 6G.

One-step synthesis and assembly of gold nanochains using the Langmuir monolayer of long-chain ionic liquids and their applications to SERS

Gold nanochains were prepared at the air/water interface under the Langmuir monolayer of a long-chain ionic liquid 1-hexadecyl-3-methylimidazolium bromide (C16mimBr) through the reduction of AuCl4− ions by UV-light irradiation. It is revealed that these nanochains are self-assembled from gold nanoparticles about an average diameter of 15 nm. The synthesis and assembly of the Au nanoparticles can be achieved in one step. It is found that the structures of the nanochains are mainly dependent on reaction temperature. Both the π–π interactions and the steric hindrance play important roles in the formations of the nanochains. The application of the thin film of Au nanochains as a substrate for surface-enhanced Raman scattering (SERS) was demonstrated. Interestingly, the enhancement property depended on the temperature. This means the effective “hot spot” of the metal nanochains are dependent on their lengths, which may be controlled by the temperature.

Galvanic replacement mediated growth of dendritic gold nanostructures with a three-fold symmetry and their applications to SERS

Hierarchical, three-fold symmetrical, single-crystalline gold dendrites are synthesized on different metal substrates including Al, Zn, and Ni in a mixture of ethanol and water with the assistance of an ionic liquid. Structural characterizations suggest that the obtained gold dendrites are grown along the directions. Such -oriented gold dendrites are seldom reported. Both the metal substrate and the volume ratio of ethanol and water have demonstrated a significant effect on the dendrite morphologies. The obtained gold dendrites are found to yield large SERS enhancement factors for rhodamine 6G (R6G) and the morphology of the branches is a key for the enhancement.

Facile preparation of CaCO3 nanocrystals with unique morphologies controlled by supramolecular complexes

A facile and effective method to synthesize dendrite-shaped calcium carbonate (CaCO3) nanocrystals in aqueous solutions of dodecyltrimethylammonium bromide (DTAB) and β-cyclodextrin (β-CD) is reported. It has been demonstrated that the supramolecular host–guest complexes formed by DTAB and β-CD play a key role in the fabrication of these unique CaCO3 nanocrystals. In order to systematically study the effect of the cationic surfactant, 1-dodecyl-3-methylimidazolium bromide (C12mimBr) and didodecyltrimethylammonium bromide (DDAB) were also used. The results show that the structures of the complexes formed by different cationic surfactants with β-CD have a strong impact on the final morphologies of the CaCO3 nanocrystals. Moreover, the interaction energies between β-CD and cationic surfactant molecules were calculated using molecular mechanics, and a possible mechanism for the formation of CaCO3 nanocrystals was proposed.

Patterns of gold nanoparticles formed at the air/water interface: effects of capping agents.

Gold nanoparticles stabilized with different capping agents were synthesized in a two-phase liquid-liquid system and found to self-assemble into various patterns at the air/water interface. The shapes of the patterns are closely related to the molecule structures of the capping agents. Systems with mixed capping agents were also investigated, and honeycomb patterns can be obtained in this way. T-shape and H-shape patterns were also observed. A possible mechanism based on Marangoni-Benard convection in evaporating droplets is proposed.

Synthesis of Silver Nanoparticles in Ionic Liquid by a Simple Effective Electrochemical Method

A simple effective electrochemical method was employed to synthesize large-sized anisotropic hexagonal and simultaneously smaller isotropic monodispersed spherical Ag nanoparticles in an ionic liquid. The electrolytic time was shortened remarkably, the dosage of stabilizers was much lowered and mechanical stirring can be needless when ionic liquid was used as a substitute for water in the electrolytic reaction.

Drug-Induced Phase Transition from Cubic Phase to Vesicle

The effect of caffeine on the phase behavior of aqueous dispersion of cubic phase was studied. The morphologies of the dispersed particles were observed by means of cryo-transmission electron microscopy (TEM) and the sizes of the dispersed particles were determined by dynamic light scattering (DLS). It was found that the addition of caffeine could lead to the phase transition from cubic phase to vesicle, and this might be due to the “salt out” effect of caffeine on the monoglyceride molecules in aqueous phase.