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Query: UMLS:C1275122 (TEM)
 21,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A one-pot, soft-chemistry, surfactant-assisted co-assembly approach to prepare La(1-x)Sr(x)MnO(3) (LSM)/Y(2)O(3)-stabilized ZrO(2) (YSZ) nanocomposites for use as solid oxide fuel cell (SOFC) cathodes has been investigated. This material with sub-hundred nanometer grain sizes for each phase is the first such nanocomposite where aqueous-based precursors of each component are incorporated in a single synthetic step. This approach utilizes the co-assembly of an anionic yttrium/zirconium acetatoglycolate gel, cetyltrimethylammonium bromide as the cationic surfactant template, and inorganic La, Mn, and Sr salts under alkaline aqueous conditions. The resulting as-synthesized product is an amorphous mesostructured organic/inorganic composite, which is transformed to a mesoporous inorganic oxide with nanocrystalline YSZ walls upon calcination. Calcination to temperatures above 600 degrees C lead to collapse of the mesopores followed by further crystallization of the nanocrystalline YSZ phase and a final crystallization of the LSM perovskite phase above 1000 degrees C. Both the fully crystalline LSM/YSZ and the mesoporous intermediate phase have been investigated for phase homogeneity by TEM energy-dispersive X-ray spectroscopy (EDX) mapping and spot analysis which confirm the dispersion of LSM within a YSZ matrix at the nanometer scale. Impedance spectroscopy analysis of LSM/YSZ nanocomposite electrodes demonstrate a low polarization resistance of around 0.2 omega cm(2) with an activation energy (E(a)) as low as 1.42 eV. Cathodic polarization studies show stable current densities over a 40 h test demonstration.
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PMID:Lanthanum strontium manganite/yttria-stabilized zirconia nanocomposites derived from a surfactant assisted, co-assembled mesoporous phase. 1270 68

The optimization of DNA-cationic polymer complexation is crucial for nonviral gene delivery. Although physicochemical characterization of the interaction between DNA and cationic polymers has recently attracted more attention in the nonviral DNA delivery field, the literature on the effect of varying polycation charge density on DNA-cationic polymer complexation is still scarce. Thus, the aim of this study was to systematically assess the influence of the degree of ionization of a weak cationic polyelectrolyte (poly[2-(dimethylamino)ethyl methacrylate] or DMAEMA homopolymer) on its ability to form complexes with DNA. This was achieved by varying the solution pH from 4.0 to 8.0 and analyzing the resulting effects on the binding affinity, thermodynamic properties, complex size, and morphology. Lowering the solution pH led to higher degrees of ionization for the cationic polymer and hence greater binding affinities with DNA, as judged by the increased propensity of the former to displace ethidium bromide from DNA and also by relatively low monomer:nucleotide molar ratio (0.8:1) required to retard the migration of free DNA. Isothermal titration microcalorimetry studies further confirmed that a stronger interaction occurred at low pH than at high pH. By decreasing the pH from 8.0 to 6.6, K(obs) increased from 7.8 x 10(5) to 20.4 x 10(5) M(-1). More efficient condensation at low pH was demonstrated by the reduction of ethidium bromide fluorescence in the loading wells from gel electrophoresis, decreased complex sizes without agglomeration occurring at high polymer/DNA ratios, together with discrete and dense spherical complexes observed in TEM studies. This may be attributed to the presence of electrostatic stabilization from excess cationic polymer chains, which provide a repulsive shell around the polymer/DNA complex. The physicochemical data indicate that the increased degree of ionization for the DMAEMA homopolymer at lower pH results in higher binding affinity, smaller and more compact complexes, and more efficient condensation. These findings therefore highlight the importance of the degree of ionization on DNA complex formation for weak cationic polyelectrolytes.
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PMID:Effect of polymer ionization on the interaction with DNA in nonviral gene delivery systems. 1274 85

Single-walled carbon nanotubes were functionalized along their sidewalls with phenol groups using the 1,3-dipolar cycloaddition reaction. These phenols could be further derivatized with 2-bromoisobutyryl bromide, resulting in the attachment of atom transfer radical polymerization initiators to the sidewalls of the nanotubes. These initiators were found to be active in the polymerization of methyl methacrylate and tert-butyl acrylate from the surface of the nanotubes. However, the polymerizations were not controlled, leading to the production of high molecular weight polymers with relatively large polydispersities. The resulting polymerized nanotubes were analyzed by IR, Raman spectroscopy, DSC, TEM, and AFM. The nanotubes functionalized with poly(methyl methacrylate) were found to be insoluble, while those functionalized with poly(tert-butyl acrylate) were soluble in a variety of organic solvents. The tert-butyl groups of these appended polymers could also be removed to produce nanotubes functionalized with poly(acrylic acid), resulting in structures that are soluble in aqueous solutions.
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PMID:Polymerization from the surface of single-walled carbon nanotubes - preparation and characterization of nanocomposites. 1467 93

The phenomenon of two dilute aqueous phases composed of sodium dodecylsulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) was investigated under various conditions such as concentrations and molar ratios of the two surfactants, the addition of sodium chloride and temperature. Vesicles formation was found in the both phases by TEM image.
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PMID:Study on aqueous two-phase systems of the mixture SDS/CTAB surfactants. 1513 55

The formation of mixed aggregates has been investigated on a ternary system consisting of two cationic surfactants with similar polar heads and two and/or one 12 carbon atom hydrophobic tail, respectively, didodecyldimethylammonium bromide and dodecylethyldimethylammonium bromide and water. The study has been carried out by means of conductivity, zeta potential, and cryogenic transmission electronic microscopy (cryo-TEM) experiments on the very diluted region. A variety of mixed aggregates, microaggregates, vesicles, and micelles has been found, depending on system composition and total surfactant concentration. Mixed critical microaggregate concentration and mixed critical vesicle concentration have been determined from conductivity data. Furthermore, zeta potential and cryo-TEM experiments allow for the characterization of the aggregates/solution interface and of the shape and size of the aggregates. This experimental evidence has also been analyzed in terms of the theoretical packing parameter, P.
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PMID:Mixed vesicle formation on a ternary surfactant system: didodecyldimethylammonium bromide/dodecylethyldimethylammonium bromide/water. 1527 64

Well-dispersed crystalline tin dioxide (SnO2) nanoparticles were synthesized by a novel and simple water-in-oil (w/o) microemulsion-assisted hydrothermal process, using low-cost tin chloride as the starting material. The typical quaternary microemulsions of cetyltrimethylammonium bromide (CTAB)/n-pentanol/n-hexane/water were used as space-confined microreactors for the nucleation, growth, and crystallization of SnO2 nanoparticles under hydrothermal conditions. The techniques of XRD, TEM, HRTEM, SAED, EDS, FTIR, XPS, and N2 adsorption measurement were used to characterize the compositions and structures of obtained samples. The results show that the SnO2 nanoparticles have high specific areas (107-169 m2 g(-1)), small particle sizes (ca. 3.0 nm), high crystallinity, and narrow size distributions. The well-dispersed, uniform, and well-crystallized powders with microporous texture are favorable for gas-sensing applications. The as-developed microemulsion-assisted in situ crystallizing process can be extended to prepare other oxide, metal, and sulfide nanoparticles.
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PMID:Novel synthesis of well-dispersed crystalline SnO2 nanoparticles by water-in-oil microemulsion-assisted hydrothermal process. 1538 Apr 22

A variety of synthesis parameters for the preparation of gold nanoparticles by NaBH4 solution reduction in the W/O microemulsion media consisting of Cetyl Trimethyl Ammonium Bromide (CTAB)/n-hexanol/water system was investigated. The results showed that the molar ratio of water to surfactant (rw) had nothing to do with the gold particle size, but the concentration of the aqueous gold salt solution had a significant effect on the size of gold particle. Through optimizing the preparation parameters, Au/Al2O3 catalysts were prepared with two different methods, then the catalysts were characterized by ultraviolet-visible spectra, XRD and TEM, and the effect of two different preparation methods on active component gold particle size in the catalysts was studied.
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PMID:[Study on the ultraviolet-visible spectra of Au/Al2O3 catalysts]. 1576 32

Ten penicillinase plasmids of varying taxonomic origin were studied after transfer to a variety of bacterial hosts. Nine of the ten plasmids specified enzymes with the following identical, or very similar, properties: substrate profile, molecular weight, susceptibility to heat and inhibitors, and electrophoretic mobility, i.e., TEM-like enzymes. The tenth R-mediated beta-lactamase was a cephalosporinase. Plasmids with TEM-like enzymes mediated resistance patterns identical towards the beta-lactam drugs, whereas the resistance pattern of the cephalosporinase plasmid was distinctly different. Expression of enzyme and resistance had a dual R-factor and host specificity. Escherichia coli K-12 and Salmonella typhi constituted one group of the same R-factor phenotype expressions. Most, but not all, penicillinase plasmids exhibited in Proteus PM1 a considerably lower order of beta-lactamase activity and an even lower order of resistance to the beta-lactam drugs than the previous two hosts. This difference was most pronounced for the resistance to carbenicillin, which was mediated by the plasmids specifying the synthesis of TEM-like enzymes. Release by osmotic shock was complete in the host E. coli K-12 for the TEM-like enzymes, but was lower for the cephalosporinase and minimal or negative in the PM1 host. Crypticity factor for benzylpenicillin, ampicillin, and carbenicillin was not related to the increase in resistance mediated by the penicillinase plasmids in both K-12 and PM1 hosts. Inoculum size effects for the penicillins and 6-aminopenicillanic acid were higher in PM1 than in K-12 R(+) cultures. The expression of penicillinase plasmids in wild-type bacteria was strain specific and not species specific. For two plasmids of different phenotypes for beta-lactamase activity (and resistance) in K-12 and PM1 hosts, a positive correlation was found between their phenotype and the relative amount of episomal deoxyribonucleic acid, as detected by ethidium bromide density gradient centrifugation. This is interpreted as indicating differences in the mode of replication of the plasmids in the two hosts.
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PMID:R-mediated beta-lactamases and episomal resistance to the beta-lactam drugs in different bacterial hosts. 1582 72

Dilute dispersions of the synthetic bilayer forming double-chained cationic lipid dioctadecyldimethylammonium bromide (DODAB) were investigated. In dispersions sonicated above the chain melting temperature Tm (approximately 45 degrees C) it was found by H NMR that about 50% of the surfactant chains remained fluid when the samples were cooled to room temperature, which is 20 degrees C below Tm. In contrast, there was no sign of a fluid fraction in unsonicated samples at room temperature. The addition of the anionic surfactant sodium dodecyl sulfate (SDS) to DODAB dispersions at room temperature resulted in the formation of an essentially stoichiometric DODA-DS complex with frozen chains, as seen by titration calorimetry and H NMR experiments. For sonicated samples, turbidity experiments demonstrated that, after a fast complexation reaction, the system remains colloidally stable unless the SDS-to-DODAB mixing ratio is too close to unity. H NMR experiments also showed that in the unreacted DODAB the fraction of fluid chains remained close to 50%, indicating either that SDS reacts equally fast with fluid and frozen DODAB or that there is a relaxation of the fluid fraction after the complexation. The melting enthalpy and the melting temperature of the alkyl chains rise gradually as the mixing ratio increases. We observed with cryo-TEM that the fraction of large unilamellar vesicles was significantly larger after addition of SDS. This indicates vesicle fusion. Based on both wide- and small-angle X-ray scattering patterns, the structure of the equimolar SDS-DODAB complex at 25 degress C was proposed to be lamellar.
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PMID:Temperature quenched DODAB dispersions: fluid and solid state coexistence and complex formation with oppositely charged surfactant. 1596 78

Surfaces of Wyoming SWy-2-Na-montmorillonite were modified using ultrasonic and hydrothermal methods through the intercalation and adsorption of the cationic surfactant octadecyltrimethylammonium bromide (ODTMA). Changes in the surfaces and structure were characterized using X-ray diffraction (XRD), thermal analysis (TG), and electron microscopy. The ultrasonic preparation method results in a higher surfactant concentration within the montmorillonite interlayer when compared with that from the hydrothermal method. Three different molecular environments for surfactants within the surface-modified montmorillonite are proposed upon the basis of their different decomposition temperatures. Both XRD patterns and TEM images demonstrate that SWy-2-Na-montmorillonite contains superlayers. TEM images of organoclays prepared at high surfactant concentrations show alternate basal spacings between neighboring layers. SEM images show that modification with surfactant reduces the clay particle size and aggregation. Organoclays prepared at low surfactant concentration display curved flakes, whereas they become flat with increasing intercalated surfactant. Novel surfactant-modified montmorillonite results in the formation of new nanophases with the potential for the removal of organic impurities from aqueous media.
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PMID:Modification of Wyoming montmorillonite surfaces using a cationic surfactant. 1614 47


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