Mingwei Zhao

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.

Liquid crystalline phases of the amphiphilic ionic liquid N-hexadecyl-N-methylpyrrolidinium bromide formed in the ionic liquid ethylammonium nitrate and in water.

The phase behavior of a surfactant-like ionic liquid, N-hexadecyl-N-methylpyrrolidinium bromide (C(16)MPB), was studied in both water and a room temperature ionic liquid, ethylammonium nitrate (EAN). Polarized optical microscopy (POM) and small-angle X-ray scattering (SAXS) measurements were employed to investigate the phase behavior of the two systems and to determine which lyotropic liquid crystalline (LC) phases were formed. With increasing C(16)MPB concentration, an isotropic solution phase, a hexagonal (H(1)) phase, and a cubic phase (V(2)) are all present in either EAN or H(2)O. The structural parameters of the H(1) phase were calculated from SAXS patterns, which show the structural changes as a function of the amount of C(16)MPB. The rheological results reveal that the H(1) phase constructed by C(16)MPB in EAN displays a typical Maxwell behavior, whereas the H(1) phase formed by C(16)MPB in water shows a gel-like behavior, unlike traditional cationic surfactants. POM and differential scanning calorimetry (DSC) results demonstrate that the lyotropic LC phase in EAN has a higher thermal stability than that formed in H(2)O, which may be important to extend the applications of the LC phase.

Aggregation behavior of gemini pyrrolidine-based ionic liquids 1,1′-(butane-1,4-diyl)bis(1-alkylpyrrolidinium) bromide ([Cnpy-4-Cnpy][Br2]) in aqueous solution

Three gemini pyrrolidine-based ionic liquids, 1,1-(butane-1,4-diyl)bis(1-alkylpyrrolidinium) bromide ([C(n)py-4-C(n)py][Br(2)], n=10, 12, 14), were synthesized. Their aggregation behavior in aqueous solution was systematically investigated by surface tension, electrical conductivity, and steady-state fluorescence. Compared with their corresponding monomers, N-alkyl-N-methylpyrrolidinium bromide (C(n)MPB), [C(n)py-4-C(n)py][Br(2)], have higher surface activity. The special structure of [C(n)py-4-C(n)py][Br(2)] that has a spacer in their hydrophilic head groups results in a lower surface excess concentration (Γ(max)) and a larger molecular cross-sectional area (A(min)). Electrical conductivity studies show a lower degree of counter-ion binding to the aggregates. A smaller aggregation number (N(agg)) is observed by the pyrene fluorescence quenching method. A series of thermodynamic parameters (ΔG(agg)(0),ΔH(agg)(0),-TΔS(agg)(0)) of aggregation derived from electrical conductivity indicate that the aggregation of [C(n)py-4-C(n)py][Br(2)] is enthalpy-driven, while aggregation of C(n)MPB is entropy-driven at low temperatures but enthalpy-driven at high temperatures.

Synthesis of Well-Dispersed NiO Nanoparticles with a Room Temperature Ionic Liquid

NiO nanoparticles have been prepared in a room temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4). The morphology and microstructures of the NiO nanoparticles were investigated by transmission electron microscopy (TEM) and x-ray diffraction (XRD). The TEM micrographs indicated that the nanoparticles are uniform hexagons and well-dispersed. From the XRD patterns, the nanoparticles could be identified as cubic phase. In the reaction, bmimBF4 is likely to act as a stabilizer and as a template, controlling the dispersion and morphology of the product.