Yuanyuan Geng

Free-standing poly(2-vinylpyridine) foam films doped with silver nanoparticles formed at the planar liquid/liquid interface.

Free-standing films of poly(2-vinylpyridine) doped with Ag(+) ions were fabricated at the planar liquid/liquid interface of an aqueous solution of AgNO(3) and a chloroform solution of the polymer through adsorption of the polymer molecules, combination with Ag(+) ions, and self-assembly of the composite species. Transmission electron microscopic (TEM) investigations indicated that the films were composed of planar thin layers decorated with separated microcapsules and foam structures of conglutinated microcapsules, and no Ag nanoparticles formed in the pristine films. After UV-light irradiation and KBH(4) aqueous solution treatment, Ag nanoparticles with the average size of 3.2 nm appeared and incorporated in the polymer matrices. X-ray photoelectron spectra (XPS) and UV-vis spectra are consistent with the TEM observations. Thermogravimetric analysis (TGA) showed good thermal stability of the composite films. The silver content was estimated to be 24.0% from the TG curve, closing to the calculated value. The catalytic performance of the composite films was evaluated by using the reduction of nitro-compounds, including nitrobenzene, 4-nitrophenol, and 4-nitrobenzoic acid by KBH(4) in aqueous solutions. The results indicated that the composite films have high and durable catalytic activity. The apparent reaction constants are related to the size of the nitro-compounds, suggesting that the Ag nanoparticles were incorporated in the matrices, and the diffusion of the reactant molecules has a great influence on the catalytic reaction.

Fabrication of composite thin films with microstructures of honeycomb, foam, and nanosphere arrays through adsorption and self-assembly of block copolymers at the liquid/liquid interface

The adsorption and self-organization behaviors of two kinds of block copolymers, polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and poly(4-vinylpyridine)-block-polystyrene-block-poly(4-vinylpyridine) (P4VP-b-PS-b-P4VP), at planar liquid/liquid interfaces were investigated. A gel film decorating with honeycomb-like microstructures forms at the liquid/liquid interface between PS-b-P4VP chloroform solution and chloroauric acid aqueous solution. However, foam films were developed when the chloroauric acid aqueous solution was replaced by a chloroplatinic acid solution or a silver nitrate solution. Furthermore, a free-standing film containing the ordered arrays of nanospheres appeared at the liquid/liquid interface between P4VP-b-PS-b-P4VP chloroform solution and chloroauric acid aqueous solution. The formation of these microstructures was attributed to the adsorption of polymer molecules, combining with inorganic ions and the self-assembly of the composite species at the interface. The doped metal ions and complex ions were transformed to metal nanoparticles after further treatment. This is a facile and convenient method to prepare polymer/inorganic nanoparticle composites. These results also indicate the great influences of the polymer structures and the inorganic species in the aqueous phases on the self-assembly behaviors of the polymers at the interfaces, the final morphology, and structure of the composites. In addition, the formed thin composite films doped with well-dispersed, homogeneous small noble metal nanoparticles exhibit great and durable catalytic activities for the reduction of 4-nitrophenol (4-NP) by potassium borohydride.

Fabrication of composite polymer foam films at the liquid/liquid interface through emulsion-directed assembly and adsorption processes.

The foam films of polystyrene-b-poly(acrylic acid)-b-polystyrene (PS-b-PAA-b-PS) doped with Cd(II) or Pb(II) species were fabricated at the planar liquid/liquid interfaces between a DMF/chloroform (v/v: 1/1) solution of the polymer and aqueous solutions containing cadmium acetate or lead acetate at ambient temperature. Optical microscopic observation shows the thin film is uniform on a larger length scale. Transmission electron microscopic (TEM) investigations reveal that the foam films are made up of microcapsules with the size of several hundreds of nanometers to micrometers. The walls of the microcapsules have a layered structure decorating with nanofibers and hollow nanospheres, where numerous inorganic fine nanoparticles are dispersed homogeneously. The film formation is a result of emulsion droplet-templated assembly and adsorption of the formed microcapsules at the planar liquid/liquid interface. Because of the miscibility of DMF with chloroform and water, DMF migrates to the aqueous phase while water migrates to the organic phase across the interface, resulting in the formation of a W/O emulsion, as revealed by optical microscopic observation, freeze fracture transmission electron microscopic (FF-TEM) observation, and dynamic laser scattering (DLS) investigation. The triblock copolymer molecules and the inorganic species adsorb and self-assemble around the emulsion drops, leading to the formation of the composite microcapsules. X-ray photoelectron spectroscopic (XPS) and FTIR spectroscopic results indicate that two kinds of Cd(II) or Pb(II) species, metal oxide or hydroxide, resulting from the hydrolysis of the metal ions and the coordinated metal ions to the carboxyl groups coexist in the formed thin films, which transform to metal sulfide completely after treating with hydrogen sulfide to get metal sulfide nanoparticle-doped polymer thin films.

Unique self-assembly behavior of amphiphilic block copolymers at liquid/liquid interfaces

Diblock copolymers (polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP)) with different molecular weights self-assembled into various supramolecular microstructures at the polymer chloroform solution/aqueous chloroauric acid interface under different conditions. Generally, multilayered foam films composed of microcapsules with walls decorated with or without round interfacial micelles formed when using a higher concentration of aqueous solution; honeycomb monolayers appeared with decreasing aqueous solution concentration; fish net-like or labyrinthine monolayers were generated with a further decrease in aqueous concentration. The appearance of these microstructures reflects the different adsorption and self-assembling behaviors of PS-b-P2VP including interfacial micellization, encapsulation, and microphase separation under different conditions. In addition, the relative molecular weights of the two blocks and the total molecular weight of the polymers had a large effect on the adsorption and self-assembly of the polymers and on the final microstructure architecture. Furthermore, the factors that affect the adsorption rate and intermolecular interactions of the polymers and, consequentially, the self-assembling behavior and final microstructure are discussed. The catalytic activities of these composite microstructures were evaluated.

Surface morphology of {100} faces of L-arginine phosphate monohydrate single crystals investigated by atomic force microscopy

Surface morphology of (100) faces of LAP crystals was investigated by atomic force microscopy (AFM). Both the steps and the two-dimensional nuclei elongate along the b direction, which is determined by the crystal structure. Fluctuations in the growth conditions could result in the formation of protuberances on the step fronts. Tree-like growth belts are initially observed on LAP crystals. It is assumed that the formation is caused by uneven liquid flow of the mother solution.

EX SITU ATOMIC FORCE MICROSCOPY STUDIES OF GROWTH MECHANISMS OF MANGANESE MERCURY THIOCYANATE CRYSTALS

Growth mechanisms of the {110} planes of the manganese mercury thiocyanate, MnHg(SCN)4 (MMTC), crystals have been investigated by using atomic force microscopy (AFM). The results show that spiral dislocation controlled mechanism and two-dimensional (2D) nucleation mechanism operate simultaneously during growth. 2D nuclei are found to cover up the outcrop of dislocation hillocks. Pairs of circular 2D nuclei appear on the wider steps terraces and the slope of 2D nucleation islands. Hillocks introduced by both simple spiral dislocation sources and 2D nucleation are elliptical in shape. It is determined the long sides orientate along the c-direction or the direction about 45° to the c-axis. Anisotropic growth hillocks and isotropic 2D nuclei coexist on the surface, which may be due to unequal supersaturations in the mother solution during the evaporation process.

ATOMIC FORCE MICROSCOPY STUDIES ON GROWTH STEPS AND 2D NUCLEI ON THE {100} FACES OF DEUTERATED L-ARGININE PHOSPHATE CRYSTALS

Growth steps and 2D nuclei of the {100} faces of the deuterated L-arginine phosphate (DLAP) crystals have been studied using ex-situ atomic force microscopy (AFM). Straight steps along the b direction as well as meandered steps are detected. The bunched steps have wider terraces than the elementary ones, which are supposed to result from the slower growth rate of the former than the latter. Many 2D nuclei exist on the step terraces and edges acting as the growth sources. Occasionally, 2D islands generated by 2D nuclei could also be observed. In conclusion, the crystal grows by layer growth mechanism.

Dislocation Growth And Microcrystal Formation Of Manganese Mercury Thiocyanate Crystals

Dislocation growth and microcrystals are investigated on the {110} faces of MMTC crystals grown from aqueous solution. Growth of MMTC crystals occurs in elementary steps (~ 0.81 nm), introduced by both simple and complex dislocation sources. The bright particles with regular sizes and shapes are assumed to be microcrystals transferred from aggregates that deposit on the faces during the crystal growth.

GROWTH HILLOCKS ON THE {100} FACES OF L-ARGININE PHOSPHATE MONOHYDRATE SINGLE CRYSTALS INVESTIGATED BY ATOMIC FORCE MICROSCOPY

Growth hillocks on the {100} faces of L-arginine phosphate monohydrate (LAP) single crystals grown at 25°C and at a supersaturation of 0.32 have been discussed. The typical dislocation growth hillocks are lopsided and elongate along the b direction. The dislocation sources are probably caused by the extra stress field which is introduced by the hollow cavities distributing on the steps and hillocks generated by the two-dimensional nucleus. The elongated shape is due to the characteristic structure of the LAP crystal. Apart from that, the formation of the lopsided growth hillocks is explained by the liquid flow theory.