Zhenguo Zhao

Preparation of BaSO4 nanoparticles in non-ionic w/o microemulsions

Abstract Spherical and cubic BaSO 4 nanoparticles with barite structure were synthesized in Triton X-100/ n -hexanol/cyclohexane/water water-in-oil microemulsions by mixing two separately prepared microemulsions containing (NH 4 ) 2 SO 4 and Ba(OAc) 2 , respectively. The effects of water content and the presence of (NH 4 ) 2 SO 4 on the size of the microemulsion droplets were investigated by dynamic light scattering. Particle characterization was accomplished by transmission electron microscopy and the effects of water content, holding time, surfactant content and reactant concentration on the particle characteristics were studied. Due to the cage-like nature of the microemulsion droplets, the size of the microemulsion droplets has a controlling effect upon the size of the particles prepared. As the water-to-surfactant molar ratio increases, both the particle size and its polydispersity increase in general. The particle shape was found to convert from spherical to cubic as the water content in the microemulsions increases. It has been shown that monodisperse cubic BaSO 4 nanoparticles can be produced inside spherical microemulsion droplets under suitable conditions.

Investigation on the conductivity and microstructure of AOT/non-ionic surfactants/water/n-heptane mixed reverse micelles

Abstract Properties and microstructures of mixed reverse micelles of anionic surfactant AOT and non-ionic surfactants in n -heptane were investigated using conductivity and dynamic light scattering. As in the reverse micelle formed with AOT alone, a conductivity maximum was also observed in conductivity- W 0 (molar ratio of water to surfactants) curves for mixed reverse micelles, and W 0,max (the W 0 where the conductivity reaches its maximum) moved to a smaller W 0 value with increasing non-ionic surfactant content and EO chain length. When NaCl solutions were solubilized by the mixed reverse micelles, the W 0,max moved to a larger W 0 value with increased concentration of NaCl solutions. These phenomena were interpreted in terms of the proposed physical meaning of W 0,max and the results of dynamic light scattering. The relationship between the conductivity of reverse micelles and their microstructures was discussed.

Synthesis and characterization of mixed CdSZnS nanoparticles in reverse micelles

Abstract Three different types of mixed CdSZnS semiconductor nanoparticles were synthesized in reverse micelles and were characterized by optical absorption and photoluminescence (PL) spectroscopy. The coprecipitated ZnxCd1−xS nanoparticles, comprised of homogeneously mixed crystals, show a continuously tunable energy gap from single CdS nanoparticles to ZnS nanoparticles. Coating the CdS core particles with a layer of ZnS in reverse micelles leads to ZnS-coated CdS (CdS/ZnS) nanoparticles with a core-shell structure, which show absorption and PL characteristics which differ considerably to those of either the coprecipitated particles or the sum of the separate particles. The intensity of the PL band centered at 630 nm, which arises from the coated CdS/ZnS nanoparticles, shows a maximum at a Zn/Cd molar ratio of about 1:1 on increasing the Zn/Cd ratio when the total concentration of CdS and ZnS is kept constant. CdS-coated ZnS (ZnS/CdS) nanoparticles synthesized in reverse micelles have absorption spectra similar to those of the coated ZnS/CdS nanoparticles but show no significant luminescence activation.

Solubilization behavior of mixed reverse micelles: effect of surfactant component, electrolyte concentration and solvent

Abstract Solubilization of water and aqueous NaCl solution in mixed reverse micellar systems formed with anionic surfactant AOT and nonionic surfactants in cyclohexane, n-hexane, n-heptane, n-octane and isooctane was studied. It was found that, for mixed reverse micelles, a maximum solubilization capacity of water occurred in the presence of a certain concentration of NaCl electrolyte which is indicated as Cmax. Cmax increased with increasing the content and EO chain length of the nonionic surfactant, and was significantly influenced by the solvent used. The physical meaning of Cmax was studied using dye-solubilization and percolation conductivity measurements. The solubilization capacity of water in reverse micellar systems was determined by two factors, the stability of the microdroplet interfacial film and the size of the microdroplet. For a reverse micellar system at constant temperature, a maximum solubilization capacity of water can be obtained by regulating the surfactant composition, the electrolyte content and the solvent.

Fluorescence probing of mixed reverse micelles formed with AOT and nonionic surfactants in n-heptane

Abstract The nature of the aqueous core of mixed reverse micelles formed with AOT and nonionic surfactants in n-heptane was investigated by fluorescence techniques. The emission properties of 1,8-anilinonaphthalenesulfonic acid (ANS) and tris(2,2′-bipyridine)ruthenium dichloride hexahydrate (Ru(bpy)32+) were found to be extremely sensitive to the solubilized water content. The fluorescence intensity decreases with increasing water content while the position of the emission maximum λmax shifts to longer wavelengths. The λmax of the fluorescence probe also depends on the added nonionic surfactant content and their EO chain length. The microstructure of the waterpool and the effect of added nonionic surfactants were studied by the fluorescence analysis of the two fluorescence probes from the viewpoint of their different location in mixed reverse micelles.

Conducting properties of mixed reverse micelles

Abstract The conducting properties of mixed reverse micelles formed with AOT and other surfactants have been investigated, with the emphasis on the effect of solvents and surfactant composition. The phenomena observed were interpreted according to the formerly proposed physical meaning of W0,max, which stands for the molar ratio of water to surfactants at the conductivity maximum of reverse micellar systems, and the results obtained from dynamic light scattering.

STUDY ON PERCOLATION OF MIXED REVERSE MICELLES

Abstract The temperature-induced percolation behaviors of AOT reverse micelles in the presence of nonionic surfactants have been studied. The effects of water content, solvent and concentration of electrolyte in solubilized water have also been investigated. It was found that the percolation temperature of AOT reverse micelles was decreased by adding nonionic surfactants, and more pronounced effects were observed with the increase of EO chain length and content of nonionic surfactants. The increase of molecular volume of the solvent and the increase of concentration of the added NaCl electrolyte have shown assisting and resisting effects on the process, respectively. The apparent hydrodynamic diameter of droplets of different mixed reverse micelles has been measured using dynamic light scattering, by which the percolating mechanism of mixed reverse micelles was discussed in combination with the results obtained from conductivity measurements.

SOLUBILIZATION IN MIXED REVERSE MICELLAR SYSTEMS OF AOT/NONIONIC SURFACTANTS/n-HEPTANE

ABSTRACT Solubilization of water and aqueous NaCl solutions in mixed reverse micellar systems of anionic surfactant AOT and nonionic surfactants in n-heptane was studied. It was found that the maximum solubilization capacity of water was higher in the presence of certain concentrations of NaCl electrolyte, and these concentrations increased with the increase of nonionic surfactant content and their EO chain length. Soluibilization capacity was enhanced by mixing AOT with nonionic surfactants. The observed phenomena were interpreted in terms of the stability of the interfacial film of reverse micellar microdroplet and the packing parameter of the surfactant that formed mixed reverse micelles.

Hydrolysis of 2,4-Dinitrochlorobenzene Catalyzed by Cationic Micelles

Abstract Micellar catalysis by nine cationic surfactants of the basic hydrolysis of 2,4-dinitrochlorobenzene(DNCB) was studied. The results obtained are as follows: (I) The second-order constants k2 for the hydrolysis reaction of DNCB catalized by the cationic micelles increase by a factor of 11–100 than that in water. Plots of k2 against the surfactant concentration show an S-type curve, and the catalytic effect is observed below the critical micelle concentration(CMC) of the surfactants. (2) For a series of surfactants, there is an optimal chain length for the alkyl of the surfactants to show the greatest catalytic effect. (3) The hydrolysis rate of DNCB decreases as the base concentration increases. (4) For the surfactants with the same hydrophilic and hydrophobic groups, chlorides have advantage over bromides in enhancing the reaction rate. These results can be interpreted in term of the changes in CMC, micelle size, solubilization capacity of the micelles, binding degree of counterion et al.

Stability of dispersions of PbTiO3 powders in aqueous and nonaqueous liquids

Abstract The dispersibility and stability of the dispersions of PbTiO 3 powders in aqueous and nonaqueous liquids have been investigated. Ionic surfactants a