Electrogenerated chemiluminescence sensors using Ru(bpy)(3)(2+) doped in silica nanoparticles

A novel electrogenerated chemiluminescence (ECL) sensor based on Ru(bpy)(3)(2+)-doped silica (RuDS) nanoparticles conjugated with a biopolymer chitosan membrane was developed. These uniform RuDS nanoparticles ( similar to 40 nm) were prepared by a water-in-oil microemulsion method and were characterized by electrochemical and transmission electron microscopy technology. The Ru( bpy)(3)(2+)-doped interior maintained its high ECL efficiency, while the exterior nanosilica prevented the luminophor from leaching out into the aqueous solution due to the electrostatic interaction. This is the first attempt to branch out the application of RuDS nanoparticles into the field of ECL, and since a large amout of Ru(bpy)(3)(2+) was immobilized three-dimensionally on the electrode, the Ru( bpy)(3)(2+) ECL signal could be enhanced greatly, which finally resulted in the increased sensitivity. This sensor shows a detection limit of 2.8 nM for tripropylamine, which is 3 orders of magnitude lower than that observed at a Nafion-based ECL sensor. Furthermore, the present ECL sensor displays outstanding long-term stability.

Solvent-induced novel morphologies in diblock copolymer blend thin films

We report the morphology and phase behaviors of blend thin films containing two poly styrene-b-poly (methyl methacrylate) (PS-b-PMMA) diblock copolymers with different blending compositions induced by a selective solvent for the PMMA block, which were studied by transmission electron microscopy (TEM). The neat asymmetric PS-b-PMMA diblock copolymers employed in this study, respectively coded as a(1) and a(2), have similar molecular weights but different volume fractions of PS block (f(PS) = 0.273 and 0.722). Another symmetric PS-b-PMMA diblock copolymer, coded as s, which has a PS block length similar to that of a(1), was also used. For the asymmetric a(1)/a(2) blend thin films, circular multilayered structures were formed. For the asymmetric a(1)/symmetric s blend thin films, inverted phases with PMMA as the dispersed domains were observed, when the weight fraction of s was less than 50%. The origins of the morphology formation in the blend thin films via solvent treatment are discussed. Combined with the theoretical prediction by Birshtein et al. (Polymer 1992, 33, 2750), we interpret the formation of these special microstructures as due to the packing frustration induced by the difference in block lengths and the preferential interactions between the solvent and PMMA block.

In(OH)(3) and In2O3 nanorod bundles and spheres: Microemulsion-mediated hydrothermal synthesis and luminescence properties

Indium hydroxide, In(OH)(3), nano-microstructures with two kinds of morphology, nanorod bundles (around 500 nm in length and 200 nm in diameter) and caddice spherelike agglomerates (around 750 - 1000 nm in diameter), were successfully prepared by the cetyltrimethylammonium bromide (CTAB)/water/cyclohexane/n-pentanol microemulsion-mediated hydrothermal process. Calcination of the In(OH)(3) crystals with different morphologies (nanorod bundles and spheres) at 600 degrees C in air yielded In2O3 crystals with the same morphology. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and photoluminescence (PL) spectra as well as kinetic decays were used to characterize the samples. The pH values of microemulsion play an important role in the morphological control of the as-formed In(OH)(3) nano-microstructures from the hydrothermal process. The formation mechanisms for the In( OH) 3 nano- microstructures have been proposed on an aggregation mechanism. In2O3 nanorod bundles and spheres show a similar blue emission peaking around 416 and 439 nm under the 383-nm UV excitation, which is mainly attributed to the oxygen vacancies in the In2O3 nano-microstructures.

Didodecyldimethylammonium bromide lipid bilayer-protected gold nanoparticles: Synthesis, characterization, and self-assembly

Didodecyldimethylammonium bromide (DDAB) lipid bilayer-protected gold nanoparticles (AuNPs), which were stable and hydrophilic, were synthesized by in situ reduction of HAuCl4 with NaBH4 in an aqueous medium in the presence of DDAB. As-prepared nanoparticles were characterized by UV-vis spectra, transmission electron microscopy, dynamic light scattering analysis, and X-ray photoelectron spectroscopy. All these data supported the formation of AuNPs. Fourier transform infrared spectroscopy (FTIR) and differential thermal analysis/thermogravimetric analysis data revealed that DDAB existed in a bilayer structure formed on the particle surface, resulting in a positively charged particle surface. The FTIR spectra also indicated that the DDAB bilayer coated on the surface of AuNPs was probably in the ordered gel phase with some end-gauche defects. On the basis of electrostatic interactions between such AuNPs and anionic polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS), we successfully fabricated (PSS/AuNP)(n) multilayers on a cationic polyelectrolyte poly(ethylenimine) coated indium tin oxide substrate via the layer-by-layer self-assembly technique and characterized as-formed multilayers with UV-vis spectra and atomic force microscopy.

Fabrication of self-assembled palladium nanosheets using layered organic/inorganic hybrid as the template

In this paper, a simple route to the fabrication of palladium nanosheets is described. The interaction of palladium chloride (PdCl2) and n-octylamine salt resulted in the formation of a quasi-perovskite-type composite with a layered structure on a molecular scale. This composite can be employed as a template for preparing ultrathin Pd nanosheets when a {PdCl4}(2-) network is reduced in situ by hydrogen in toluene. The x-ray diffraction results indicate that the resulting Pd nanosheets are highly ordered, and they are confined inside the organic matrix as evidenced by high resolution transmission electron microscopy. These Pd nanosheets can be reorganized into layered structures in non-polarized organic solvent when the ordered structure is destroyed. This method of preparing Pd nanosheets is expected to be applicable to other layered organic/inorganic perovskite systems for obtaining the corresponding metal nanosheets.

An effective approach to synthesis of poly(methyl methacrylate)/silica nanocomposites

A novel synthetic route for nearly monodispersed poly(methyl methacrylate)/SiO2 composite particles (PMSCP) is reported. Silica nanoparticles modified with oleic acid were used as 'seeds'. Methyl methacrylate (MMA) monomer was copolymerized with oleic acid via in situ emulsion polymerization, in the presence of an initiator; it resulted finally in the formation of composites with core-shell morphology. The composite particles were examined by transmission electron microscopy (TEM), scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). The number of silica particles inside the composite particles increases with an increase in the silica concentration. The effect of grafted silica concentration on the morphology of PMSCP is also reported in detail. It was found by thermogravimetric analysis that PMSCP show a potential application for fire retardance.

Crystallization and phase behavior of crystalline syndiotactic 1,2-polybutadiene/isotactic polypropylene blends in solution-cast thin films

Crystallization and phase behavior in solution-cast thin films of crystalline syndiotactic 1,2-polybutadiene (s-1,2-PB) and isotactic polypropylene (i-PP) blends have been investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM) and field-emission scanning electron microscopy (FESEM) techniques. Thin films of pure s-1,2-PB consist of parallel lamellae with the c-axis perpendicular to the film plane and the lateral scale in micrometer size, while those of i-PP are composed of cross-hatched and single-crystal-like lamellae. For the blends, TEM and AFM observations show that with addition of i-PP, the s-1,2-PB long lamellae become bended and i-PP itself tends to form dispersed convex regions oil a continuous s-1,2-PB phase even when i-PP is the predominant component, which indicates a strong phase separation between the two polymers during film formation. FESEM micrographs of both lower and upper surfaces of the films reveal that the s-1,2-PB lamellae pass through i-PPconvex regions from the bottom, i.e. the dispersed i-PP regions lie on the continuous s-1,2-PB phase. The structural development is attributed to an interplay of crystallization and phase separation of the blends in the film forming process.

3-Mercaptopropionic Acid Capped Gold Nanoclusters: Quantized Capacitance in Aqueous Media

3-Mercaptopropionic add monolayer protected gold nanoclusters (MPA-MPCs) were synthesized and characterized by transmission electron microscopy, UV-Vis spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The exact value of quantized double-layer capacitance of MPCS in aqueous media was obtained by differential pulse voltammograms.

Effects of surfactant loadings on the dispersion of clays in maleated polypropylene

A series of organically modified clays (OMCs) with a surfactant loading range from 0.625 to 2.5 times the cation exchange capacity (CEC) were melt-mixed with maleated polypropylene (PPMA). Wide-angle X-ray diffraction and transmission electron microscopy results of these narrocomposites show that dispersion of clays becomes unfavorable in the PPMA matrix during melt intercalation as the surfactant loading increases in the process of modifying clays, though larger interlayer distances are obtained in their corresponding OMCs. It is even important that clays uniformly disperse at the nanoscale level in the PPMA matrix when the surfactant loadings are below the CEC, which implies that incomplete exchange of inorganic cations in the process of modifying clay benefits the dispersion of clays in the PPMA matrix.

Direct formation of form I poly(1-butene) single crystals from melt crystallization in ultrathin films

The morphologies and crystalline structures of melt-crystallized ultrathin isotactic poly(1-butene) films have been studied with transmission electron microscopy and electron diffraction. It is demonstrated that a bypass of form II crystallization can be achieved with an increase in its crystallization temperature. Electron microscopy observations show that melt-grown isotactic poly(1-butene) single crystals have a well-shaped hexagonal form, whereas form I crystals converted from form II display the morphologies of their tetragonal precursors. Electron diffraction results indicate that, instead of the twinned hexagonal pattern of the converted form I crystal, the directly formed form I single crystals exhibit an untwinned hexagonal pattern.

Preparation of polymer/silica nanoscale hybrids through sol-gel method involving emulsion polymers. II. Poly(ethyl acrylate)/SiO2

Poly(ethyl acrylate) (PEA)/SiO2 hybrids with different compositions were prepared under different casting temperatures and pH values. Their morphology as investigated by transmission electron microscopy (TEM) shows that samples with different compositions have different morphologies. When the SiO2 content is lower, PEA is the continuous phase and SiO2 is the dispersed phase. At higher SiO2 content, the change in phase morphology takes place, nd PEA gradually dispersing in the form of latex particles in SiO2 matrix. Change in phase morphology depends mainly on the time the sol-gel transition occurs. At suitable casting temperature and pH value, PEA/SiO2 in 95/5 and 50/50 hybrids with even dispersion was obtained.

In situ study of nanostructure and morphological development during the crystal-mesophase transition of poly(di-n-hexylsilane) and poly(di-n-butylsilane) by X-ray and hot-stage AFM

Nanostructure and morphology and their development of poly(di-n-hexylsilane) (PDHS) and poly(di-n-butylsilane) (PDBS) during the crystal-mesophase transition are investigated using small angle X-ray scattering (SAXS), wide angle X-ray diffraction and hot-stage atomic force microscopy. At room temperature, PDHS consists of stacks of lamellae separated by mesophase layers, which can be well accounted using an ideal two-phase model. During the crystal-mesophase transition, obvious morphological changes are observed due to the marked changes in main chain conformation and intermolecular distances between crystalline phase and mesophase. In contrast to PDHS, the lamellae in PDBS barely show anisotropy in dimensions at room temperature. The nonperiodic structure and rather small electronic density fluctuation in PDBS lead to the much weak SAXS. The nonperiodic structure is preserved during the crystal-mesophase transition because of the similarity of main chain conformation and intermolecular distances between crystalline phase and mesophase.

Branched crystal morphology of linear polyethylene crystallized in a two-dimensional diffusion-controlled growth field

The branched crystal morphology of linear polyethylene formed at various temperatures from thin films has been studied by atomic-force microscopy (AFM), transmission electron microscopy (TEM), electron diffraction (ED) pattern and polymer decoration technique. Two types of branched patterns, i.e. dendrite and seaweed patterns, have been visualized. The fractal dimension d(f) = 1.65 of both dendrite and some of seaweed patterns was obtained by using the box-counting method, although most of the seaweed patterns are compact. Selected-area ED patterns indicate that the fold stems tilt about 34.5degrees around the b-axis and polymer decoration patterns show that the chain folding direction and regularity in two (200). regions are quite different from each other. Because of chain tilting, branched crystals show three striking features: 1) the lamella-like branches show two (200) regions with different thickness; 2) the crystals usually bend towards the thin region; 3) the thick region grows faster by developing branches, thus branches usually occur outside the thick region. The branched patterns show a characteristic width w, which gives a linear relationship with the crystallization temperature on a semilogarithmic plot.

Liquid crystalline phases, microtwinning in crystals and helical chirality transformations in a main-chain chiral liquid crystalline polyester

A main-chain nonracemic chiral liquid crystalline polymer was synthesized from (R)-(-)4'-{w-[2-(p-hydroxy-o-nitrophenyloxy)-1-propyloxy]-1-decyloxyl-4-biphenylcarboxylic acid. This polymer contained 10 methylene units in each chemical repeating unit and was abbreviated PET(R*-10). On the basis of differential scanning calorimetry, wide-angle X-ray diffraction, and polarized light microscopy experiments, chiral smectic C (S-C*) and chiral smectic A (S-A*) phases were identified. Both flat-elongated and helical lamellar crystal morphologies were observed in transmission electron microscopy. Of particular interest was the flat-elongated lamellar crystals were constructed via microtwinning of an orthorhombic cell with dimensions of a = 1.42 nm, b = 1.28 nm, and c = 3.04 nm. On the other hand, the helical lamellar crystals were exclusively left-handed, which was opposite to the right-handed helical crystals grown in PET(R*-9) and PET(R*-11) (having 9 and 11 methylene units, respectively). Note that these three polymers had identical right-handed chiral centers (R*-). Therefore, a single methylene unit difference on the polymer backbones on an atomic length scale substantially changed the chirality of the crystals in the micrometer length scale. Furthermore, aggregates of these helical crystals in PET(R*-10) did not generate banded spherulites in polarized light microscopy. Possible reasons for this change and loss of helical senses (handedness) on different length scales in chirality transferring processes were discussed.

Structural electrochemical study of hemoglobin by in situ circular dichroism thin layer spectroelectrochemistry

Secondary and tertiary or quaternary structural changes in hemoglobin (HB) during an electroreduction process were studied by in situ circular dichroism (CD) spectroelectrochemistry with a long optical path thin-layer cell. By means of singular value decomposition least-squares analysis, CD spectra in the far-UV region give two similar a components with different CD intensity, indicating slight denaturation in the secondary structures due to the electric field effect. CD spectra in the Soret band show a R --> T transition of two quaternary structural components induced by electroreduction of the heme, which changes the redox states of the center ion from Fe3+ to Fe2+ and the coordination number from 6 to 5. The double logarithmic analysis shows that electroreduction of hemoglobin follows a chemical reaction with R --> T transition. Some parameters in the electrochemical process were obtained: formal potential, E-0t = -0.167 V; electrochemical kinetic overpotential, DeltaE(0) = -0.32 V; standard electrochemical reaction rate constant, k(0) = 1.79 x 10(-5) cm s(-1); product of electron transfer coefficient and electron number, alphan=0.14; and the equilibrium constant of R --> T transition, K-c = 9.0.