Primary Building Blocks Research Articles

Controlled synthesis of monodisperse α-calcium sulfate hemihydrate nanoellipsoids with a porous structure.

We report a facile and green chemical solution approach to synthesize monodisperse α-calcium sulfate hemihydrate (α-HH) nanoellipsoids with a length of 600 nm and a width of 300 nm by simply mixing Ca(2+) and SO4(2-) glycerol-water precursor solutions in the presence of Na2EDTA. The α-HH nanoellipsoid is formed through a Na2EDTA-mediated self-assembly of small primary building blocks (α-HH domains: ∼14 nm). The study on the morphological evolution of α-HH reveals that the controlled synergy of supersaturation (precursor concentration) and Na2EDTA is crucial for the development of α-HH into nanoellipsoids. Further thermal annealing of the nanoellipsoid could make the α-HH domains transit into calcium sulfate anhydrites and grow up, generating the gaps between them and resulting in a porous structure. This work paves a new way for preparing high-quality α-HH nanoellipsoids with a monodisperse nanosize and a porous structure, promising their future application in many fields such as biomedicine.

Polyacrylic Acid Assisted Assembly of Oxide Particles and Carbon Nanotubes for High‐Performance Flexible Battery Anodes

A polyacylic acid assisted assembly strategy is applied for fabrication of flexible battery anodes in which electrochemically active nanocrystals and carbon ­nanotubes are used as primary building blocks. The strong interaction between each constituent in a porous network of conductive carbon nanotubes leads to excellent rate performance and cycling stability of the electrodes.

Particle formation pathways and polymorphism of curcumin induced by ultrasound and additives during liquid antisolvent precipitation

Precipitation of curcumin, a poorly water-soluble drug, has been carried out by the liquid antisolvent technique in the presence of ultrasound and stabilizers. Curcumin particles with varied morphology were observed to have formed during precipitation in the presence of ultrasound and additives such as sodium dodecyl sulfate (SDS), Tween 80, hydroxyl propyl methylcellulose (HPMC), polyvinyl pyrrolidone (PVP), and bovine serum albumin (BSA). Characterization of the precipitated particles reveals that curcumin particles precipitated with ultrasound and large polymeric stabilizers such as HPMC, PVP, and BSA are superstructures formed by aggregation of several primary curcumin nanoparticles. The particles in these cases appeared to be loose aggregates (of ~1–5 μm in size) composed of several curcumin nanoparticles (~50–200 nm in size). On the other hand, curcumin particles precipitated in the presence of ultrasound and without additive as well as small-molecule stabilizers like SDS and Tween 80 appear more fused (the primary building blocks of these particles were not clearly visible). Moreover, curcumin particles precipitated in the presence of ultrasound only and particles precipitated in the presence of ultrasound along with additives were found to exist in the orthorhombic form, whereas raw curcumin and curcumin particles precipitated without any additive and without ultrasound were found to exist in the monoclinic form. The results obtained in this work suggest that curcumin particles with the desired physical form and morphology can be engineered through a careful manipulation/choice of ultrasound and additives during precipitation.

One-step synthesis of hematite nanospindles from choline chloride/urea deep eutectic solvent with highly powerful storage versus lithium

Fe2O3 nanospindles assembled with nanoparticles as primary building blocks are directly synthesized by a versatile ionothermal strategy in the choline chloride/urea mixture-based deep eutectic solvent system. The proposed ionothermal protocol is attractive and environmental friendly because choline chloride and urea are both naturally biocompatible compounds. As an anode material for lithium-ion batteries, the resultant Fe2O3 nanospindles show high capacity and good cycle stability (921.7 mAh g−1 at a current density of 200 mA g−1 up to 50 cycles), as well as the excellent rate capability. The good electrochemical performance can be attributed to the nanospindle structure with high sufficient interfacial contact area between the active material and electrolyte, the short diffusion distance of Li ions. The environmentally benign strategy proposed in this study is expected to offer an attractive technique for the ionothermal synthesis of electrochemical energy storage materials.

Supramolecular Nanofibers Self‐Assembled from Foldamers: Structure Control through Preassembly

AbstractWe used a helical polymer backbone (polyacrylamide) as a scaffold to organize perylene diimide chromophores into well‐defined foldamers, which further undergo self‐assembly into supramolecular tube‐like arrays in aqueous media, as revealed by cryo‐TEM imaging. The arrays are supramolecular polymers, whose structure is templated by folded primary building blocks, representing a useful tool for directing self‐assembly . Exciton migration in the supramolecular arrays was studied by transient absorption and revealed a moderate exciton diffusion propensity.

Synthesis of regiospecifically fluorinated conjugated dienamides.

Modular synthesis of regiospecifically fluorinated 2,4-diene Weinreb amides, with defined stereochemistry at both double bonds, was achieved via two sequential Julia-Kocienski olefinations. In the first step, a Z-α-fluorovinyl Weinreb amide unit with a benzothiazolylsulfanyl substituent at the allylic position was assembled. This was achieved via condensation of two primary building blocks, namely 2-(benzo[d]thiazol-2-ylsulfonyl)-2-fluoro-N-methoxy-N-methylacetamide (a Julia-Kocienski olefination reagent) and 2-(benzo[d]thiazol-2-ylthio)acetaldehyde (a bifunctional building block). This condensation was highly Z-selective and proceeded in a good 76% yield. Oxidation of benzothiazolylsulfanyl moiety furnished a second-generation Julia-Kocienski olefination reagent, which was used for the introduction of the second olefinic linkage via DBU-mediated condensations with aldehydes, to give (2Z,4E/Z)-dienamides in 50%–74% yield. Although olefinations were 4Z-selective, (2Z,4E/Z)-2-fluoro-2,4-dienamides could be readily isomerized to the corresponding 5-substituted (2Z,4E)-2-fluoro-N-methoxy-N-methylpenta-2,4-dienamides in the presence of catalytic iodine.

Unconventional Assembly of Bimetallic Au-Ni Janus Nanoparticles on Chemically Modified Silica Spheres

This paper reports that Janus Au-Ni nanoparticles (JANNPs) can self-assemble onto silica spheres in a novel way, which is different from that of single-component isotropic nanoparticles. JANNPs modified with octadecylamine (ODA) assemble onto catechol-modified silica spheres (SiO2-OH) to form a very special core-loop complex structure and finally the core-loop assemblies link each other to form large assemblies through capillary force and the hydrophobic interaction of the alkyl chains of ODA. The nanocomposites disassemble in the presence of vanillin and oleic acid because of the breakage of the catechol-metal link. Vanillin-induced disassembly enables the JANNPs to reassemble into a core-loop structure upon ODA addition. The assembly of SiO2-OH and isotropic Ni or Fe3O4 particles generates traditional core-satellite structures. This unconventional self-assembly can be attributed to the synergistic effect of Janus specificity and capillary force, which is also confirmed by the assembly of thiol-terminated silica spheres (SH-SiO2) with anisotropic JANNPs, isotropic Au, and Ni nanoparticles. These results can guide the development of novel composite materials using Janus nanoparticles as the primary building blocks.

Atomistic simulations, mesoscopic modeling, and theoretical analysis of thermal conductivity of bundles composed of carbon nanotubes

The propensity of carbon nanotubes (CNTs) to self-organize into continuous networks of bundles has direct implications for thermal transport properties of CNT network materials and defines the importance of clear understanding of the mechanisms and scaling laws governing the heat transfer within the primary building blocks of the network structures—close-packed bundles of CNTs. A comprehensive study of the thermal conductivity of CNT bundles is performed with a combination of non-equilibrium molecular dynamics (MD) simulations of heat transfer between adjacent CNTs and the intrinsic conductivity of CNTs in a bundle with a theoretical analysis that reveals the connections between the structure and thermal transport properties of CNT bundles. The results of MD simulations of heat transfer in CNT bundles consisting of up to 7 CNTs suggest that, contrary to the widespread notion of strongly reduced conductivity of CNTs in bundles, van der Waals interactions between defect-free well-aligned CNTs in a bundle have negligible effect on the intrinsic conductivity of the CNTs. The simulations of inter-tube heat conduction performed for partially overlapping parallel CNTs indicate that the conductance through the overlap region is proportional to the length of the overlap for CNTs and CNT-CNT overlaps longer than several tens of nm. Based on the predictions of the MD simulations, a mesoscopic-level model is developed and applied for theoretical analysis and numerical modeling of heat transfer in bundles consisting of CNTs with infinitely large and finite intrinsic thermal conductivities. The general scaling laws predicting the quadratic dependence of the bundle conductivity on the length of individual CNTs in the case when the thermal transport is controlled by the inter-tube conductance and the independence of the CNT length in another limiting case when the intrinsic conductivity of CNTs plays the dominant role are derived. An application of the scaling laws to bundles of single-walled (10,10) CNTs reveals that the transition from inter-tube-conductance-dominated to intrinsic-conductivity-dominated thermal transport in CNT bundles occurs in a practically important range of CNT length from ∼20 nm to ∼4 μm.

Influence of Silicon Nanoscale Building Blocks Size and Carbon Coating on the Performance of Micro‐Sized Si–C Composite Li‐Ion Anodes

AbstractSilicon has been intensively pursued as the most promising anode material for Li‐ion batteries due to its high theoretical capacity of 3579 mAh/g. Micro‐sized Si–C composites composed of nanoscale primary building blocks are attractive Si‐based anodes for practical application because they not only achieve excellent cycling stability, but also offer both gravimetric and volumetric capacity. However, the effects of key parameters in designing such materials on their electrochemical performance are unknown and how to optimize them thus remains to be explored. Herein, the influence of Si nanoscale building block size and carbon coating on the electrochemical performance of the micro‐sized Si–C composites is investigated. It is found that the critical Si building block size is 15 nm, which enables a high capacity without compromising the cycling stability, and that carbon coating at higher temperature improves the first cycle coulombic efficiency (CE) and the rate capability. Corresponding reasons underlying electrochemical performance are revealed by various characterizations. Combining both optimized Si building block size and carbon coating temperature, the resultant composite can sustain 600 cycles at 1.2 A/g with a fixed lithiation capacity of 1200 mAh/g, the best cycling performance with such a high capacity for micro‐sized Si‐based anodes.

Hierarchical self-assembly of miktoarm star polymers containing a polycationic segment: A general concept

We recently introduced a concept for the counterion-mediated hierarchical self-assembly of an amphiphilic ABC miktoarm star terpolymer in aqueous media into micrometer-sized compartmentalized particles with a highly periodic lamellar fine structure (“woodlice”). Herein, we extend this concept to different miktoarm star polymer systems containing a polycationic segment. The presence of a poly(N-methyl-2-vinylpyridinium) (P2VPq) block and its interaction with iodide/triiodide counterions is crucial. In analogy to linear diblock copolymer systems the hydrophilic/hydrophobic balance of polybutadiene-arm-poly(N-methyl-2-vinylpyridinium iodide)-arm-polystyrene miktoarm star terpolymers determines the morphology of the primary building blocks (spherical micelles and cylindrical micelles/vesicles) and the obtained superstructures (stacked lamellar structures and multilamellar vesicles) during this hierarchical process. When an ABA' miktoarm star copolymer (polystyrene-arm-poly(N-methyl-2-vinylpyridinium iodide)-arm-polystyrene) without a dynamic core-forming block was investigated, a different mechanism into “woodlouse” structured aggregates via aggregation and deformation of intermediate vesicles was found. The individual steps of the different self-assembly processes were investigated by transmission electron microscopy and additionally supported by dynamic light scattering, differential scanning calorimetry, and small-angle X-ray scattering.

Succinylated Octopamine Ascarosides and a New Pathway of Biogenic Amine Metabolism in Caenorhabditis elegans

The ascarosides, small-molecule signals derived from combinatorial assembly of primary metabolism-derived building blocks, play a central role in Caenorhabditis elegans biology and regulate many aspects of development and behavior in this model organism as well as in other nematodes. Using HPLC-MS/MS-based targeted metabolomics, we identified novel ascarosides incorporating a side chain derived from succinylation of the neurotransmitter octopamine. These compounds, named osas#2, osas#9, and osas#10, are produced predominantly by L1 larvae, where they serve as part of a dispersal signal, whereas these ascarosides are largely absent from the metabolomes of other life stages. Investigating the biogenesis of these octopamine-derived ascarosides, we found that succinylation represents a previously unrecognized pathway of biogenic amine metabolism. At physiological concentrations, the neurotransmitters serotonin, dopamine, and octopamine are converted to a large extent into the corresponding succinates, in addition to the previously described acetates. Chemically, bimodal deactivation of biogenic amines via acetylation and succinylation parallels posttranslational modification of proteins via acetylation and succinylation of L-lysine. Our results reveal a small-molecule connection between neurotransmitter signaling and interorganismal regulation of behavior and suggest that ascaroside biosynthesis is based in part on co-option of degradative biochemical pathways.

Morphology transformations in tetrabutyl titanate–acetic acid system and sub-micron/micron hierarchical TiO2 for dye-sensitized solar cells

The concentration of tetrabutyl titanate (TBT) and H2O influence on the reaction kinetics of TBT and acetic acid (AcOH) solvothermal system are systematically studied. It is found that TBT and H2O have greatly accelerated the hydrolysis–condensation process of the TBT–AcOH system. By adjusting those concentrations with reaction time, we prepare five kinds of sub-micron/micron precursors, which are hierarchical structures consisting of different primary building blocks. The morphology of these precursors varies from noninterlaced structures composed of flower-like microsphere and ellipsoid sphere to interlaced structures composed of flower-like microsphere interlaced nanofibers, ellipsoid spheres interlaced flower-like microsphere and nanoparticles interlaced flower-like microsphere. These interlaced structures are synthesized for the first time and are not ordinary mixtures of the noninterlaced structures. After heat treatment, these precursors are transformed to anatase TiO2. Shape-dependent photovoltaic performances of dye-sensitized solar cells (DSSCs) are also discussed. DSSCs based on these hierarchical sub-micron/micron TiO2 show 7.3%–7.9% energy conversion efficiencies, and the devices based on interlaced structures have higher efficiencies (7.4%–7.9%) than those of the devices based on noninterlaced structures (7.3%–7.6%).

Supramolecular Assemblies of a Semirigid Polyanion in Aqueous Solutions

In this article, we report the supramolecular assemblies of a semirigid polyelectrolyte, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT) in water. Cryo-TEM observation and SAXS measurement reveal that PBDT forms bundle-like structure even in very dilute concentration, CP, of 0.02 wt %. These bundle-like assemblies serve as new primary building blocks and self-assemble further as CP increases, to form large associations with or without long-range orientation. When 2 wt % < CP < 6 wt %, liquid–liquid phase separation occurs. Some of the supramolecular associations form bipolar liquid crystalline (LC) droplets via a typical nucleation and growth process. The droplets grow up by the coalescence of small ones and sediment under the gravity and coalesce to form a bottom nematic phase. When CP ≥ 6 wt %, the solutions are in a uniform nematic phase. The existence of these preliminary supramolecular assemblies of PBDT in aqueous solutions should be crucial for the formation of nematic LC phase at a significantly low CP, as well as the formation of macroscopic ordered structures in hydrogels via electrostatic interaction between PBDT and oppositely charge multivalent metallic ion or polycation.

Calculating effective growth rate from a random Leslie model: Application to incidental mortality analysis

Demographic models are commonly used to study cetacean population dynamics and are characterized by a wide range of age classes. The primary building blocks are age-specific survival or mortality and birth rates, which can be combined using a Leslie matrix protocol to provide estimates of maximum possible rates of increase for population size. In this context, specific mortality data are valuable for modeling the viability of threatened species. Depletion of prey, pollution, and other anthropogenic disturbances are believed to have contributed to the decline of populations, but the evidence is less conclusive for these factors than for bycatch. In an attempt to estimate a population growth rate that incorporates uncertainties in vital parameters, we apply a random Leslie analysis to calculate effective growth rate for the time-dependent mean-value population. Here we provide the algorithm to implement it for a general 13×13 random survival model. An effective growth rate can be characterized by studying the time evolution of the mean-value population vector state (in an age-structured description). We show that the asymptotic behavior of the mean-value vector state, which characterizes the population growth rate when the model has random vital parameters, exhibits a value that is below previously expected potential estimations. We demonstrate the procedure using bibliographic revision data of the harbor porpoise (Phocoena phocoena) in Canadian waters, subjected to incidental mortality.

An oil droplet template method for the synthesis of hierarchical structured Co3O4/C anodes for Li-ion batteries

Superposed cobalt(II)-cobalt(III) layered double hydroxide (Co(II)-Co(III)-LDH) nanoplates were synthesized by an oil droplet template method, in which the main steps are as follows: LDH nanosheets were first assembled on an oil droplet template to form a multishell sphere, and then the oil droplet was easily removed under centrifugal force due to its very different density from that of the assembled LDH shell. This resulted in the multishell spheres being split open to create superposed LDH nanoplates. The resulting material has a three-stage architecture, namely, the primary building blocks of nanosheets, the secondary architecture of shells derived from the nanosheets, and the long-range architecture of superposed nanoplates assembled from the vertically stacked shells. Most importantly, the as-fabricated LDH-based hierarchical structure can be readily converted to a Co3O4/C composite via calcination, without obvious structural alteration, where the residual surfactant is the source of the carbon. When used as an anode material for Li-ion batteries, the Co3O4/C electrode exhibits an excellent electrochemical performance, which is attributed to the unique hierarchically porous structure.

Independence in Europe: Secession, Sovereignty, and the European Union

III. THE EUROPEAN UNION AS A FORUM FOR SELF-DETERMINATION CLAIMS European integration was not always popular among nationalists in Europe's stateless nations. The SNP, for example, argued that integration amounted merely to the transfer of sovereignty over Scotland from one alien government in London to another in Brussels. (156) Yet by the 1980s, the SNP had become firm supporter of the European project and proponent of Independence in (157) Flemish nationalists have also embraced integration, and the N-VA describes itself as extremely pro-European party that supports both a stronger Flanders and stronger (158) The centrality of the EU to Catalan nationalist discourse is evident in the banners carried by demonstrators in Barcelona calling for Catalonia to become New European State, (159) in the Declaration of Sovereignty's assurance that [t]he founding principles of the European Union shall be defended and promoted, (160) and in Artur Mas's proposed wording for future referendum question: Do you want Catalonia to become new state within the European Union? (161) It is overly simplistic to conclude that the EU encourages or discourages separatism or that it makes secession easier or more difficult. Nonetheless, European integration affect[s] how the parties to [separatist] conflict perceive their own interests and identities. (162) Three aspects of the EU play particularly important role in shaping Flemish, Scottish, and Catalan self-determination claims and considering how such claims might be addressed: the respective roles of and regions in EU institutions, the rules governing EU membership, and the debates over the future of in the wake of the eurozone crisis. A. States and Regions Although it is often obscured by considerations of the EU's impact on sovereignty, the fact remains that the EU is in ways governed cooperation among the governments of its member states rather than by supranational structures with independent authority. (163) States remain the primary actors within the EU Membership in the EU is limited to sovereign that meet the EU's admissions criteria and that are admitted through unanimous vote by member states. (164) Once admitted to membership, participate directly in the EU's primary governing institutions: the European Council (consisting of ministers from each member state), the European Commission (consisting of one commissioner from each member state), and the European Parliament (consisting of elected representatives from the member states). (165) Thus, [statehood in the EU ... retains meaning for nationalists because it still remains the sole means by which nationalists can be recognized as sovereign equals in the European political system. (166) Attempts to establish formal channels for regional participation in EU governance have produced only limited results. During the 1980s and 1990s, it became popular to envision Europe of the in which local governments would replace as the primary building blocks of more fully integrated Europe. Many regions established information offices in Brussels in an effort to access the emerging European policymaking structures. (167) Bolstering the of the Regions idea was the Maastricht Treaty, which entered into force in 1993. (168) Maastricht enshrined the principle of subsidiarity (pursuant to which authority over any given area of competency should be vested at the lowest possible political level) in EU law, established Committee of the Regions, and allowed regional ministers to sit on member state delegations in the European Council where the member state deemed such participation appropriate. (169) Yet on balance, the robust regional role that the Maastricht Treaty appeared to promise has never fully materialized. According to Laible, many observers point not to the strength of regions in EU policymaking, but to their weakness. …

Performance Evaluation of 32-nm CNT-OPAMPs in Analog Circuits: Design and Comparison of Leapfrog Filters

In this paper, we have presented the design and characteristic performance evaluation of a 6-order Leapfrog Filter. First we designed the filter by using Silicon-based CMOS Operational Amplifiers (Si-OPAMPs). Then we designed the filter with Carbon Nanotube-based Operational Amplifiers (CNT-OPAMPs) using a benchmark nine-transistor Operational Amplifier (OPAMP) model with single-walled Carbon Nanotube Field-Effect Transistors (SW-CNTFETs) as primary building-blocks for 32nm technology. We compared the performance between the two and achieved higher phase margin, improved power dissipation, and significantly higher input resistance for the CNT-OPAMP based filter. Then we further evaluated the performance of the CNT-OPAMP based filter by changing the number of SWNTs used in the intrinsic channel region of the CNTFET, keeping all other design parameters the same. Our simulation-based assessment has shown a satisfactory superiority for CNT-OPAMP filter design in comparison with Si-based CMOS filter design. The results obtained suggest that the CNT-OPAMP has a promising potential for low-power, high-speed applications in both analog and mixed-signal nanoelectronic circuits.

On the origin of hot metasedimentary quartzites in the lower crust of continental arcs

Volcanic arcs associated with subduction zones are thought to be the primary building blocks of continents. The composition of the magmas, particularly in continental arcs, is the product of mixing between differentiation of juvenile magmas and pre-existing crustal wallrock, the former being typically mafic and the latter more silicic. Because the upper continental crust is on average thought to be more silicic than the mafic lower crust, mixing with silicic endmembers should occur primarily in the upper crust. However, we show here that the lower crust of continental arcs contains silicic metasediments. We examine garnet-bearing, granulite-facies sedimentary quartzite xenoliths from the Sierra Nevada batholith in California, a Cretaceous continental arc. The quartzites have equigranular textures and contain quartz (>50%), plagioclase (<30%), garnet (10%), and small amounts (<1%) of rutile, aluminosilicate, biotite, monazite, zircon, graphite and trace orthopyroxene. Cathodoluminescent images show zircons with rounded detrital cores mantled by metamorphic overgrowths. Hf isotopic model ages and U–Pb upper intercept ages, for a given zircon, are similar, but the zircon population shows variable protolith ages ranging from Proterozoic to Archean. In contrast, all zircons share similar lower intercept U–Pb ages (103±10Ma), which coincide with the peak of arc magmatism in the Sierra Nevada. The Precambrian protolith ages are similar to North American cratonal basement, and together with the abundance of quartz and detrital zircons, suggest that these quartzites represent ancient, passive margin sediments instead of juvenile active margin sediments in the oceanic trench and accretionary prism. Importantly, these quartzites record peak metamorphic temperatures and pressures of 700–800°C using Ti-in-quartz thermometry and 0.7–1.1GPa using garnet–aluminosilicate–plagioclase thermobarometry, indicating that these xenoliths experienced significant heating and possible partial melting in the lower crust, most likely related to arc magmatism as suggested by similarities between the lower intercept U–Pb ages and the ages of plutonism in the Sierra Nevada. Possible mechanisms by which these sediments were transported into the lower crust include continental underthrusting beneath the continental arc, underplating by buoyant slab-derived sedimentary diapirs, or viscous downflow of country rock in response to diapiric ascent of plutons. Continental underthrusting has been independently documented during the Sevier orogeny, coinciding with the peak of arc magmatism. We thus speculate that supracrustal rocks may have been underthrusted into deep crustal magmatic zones. Regardless of how these metasediments arrived in the lower crust, our observations indicate that silicic metasediments occur in the lower crust of volcanic arcs, not just in the upper crust as is commonly thought. Transport of metasediments into deep crustal magmatic zones should influence the composition of arc magmas and continental crust in general.

METABOLIC ENGINEERING OF BIOCATALYSTS FOR CARBOXYLIC ACIDS PRODUCTION

Fermentation of renewable feedstocks by microbes to produce sustainable fuels and chemicals has the potential to replace petrochemical-based production. For example, carboxylic acids produced by microbial fermentation can be used to generate primary building blocks of industrial chemicals by either enzymatic or chemical catalysis. In order to achieve the titer, yield and productivity values required for economically viable processes, the carboxylic acid-producing microbes need to be robust and well-performing. Traditional strain development methods based on mutagenesis have proven useful in the selection of desirable microbial behavior, such as robustness and carboxylic acid production. On the other hand, rationally-based metabolic engineering, like genetic manipulation for pathway design, has becoming increasingly important to this field and has been used for the production of several organic acids, such as succinic acid, malic acid and lactic acid. This review investigates recent works on Saccharomyces cerevisiae and Escherichia coli, as well as the strategies to improve tolerance towards these chemicals.

Role of polymeric surfactants on the growth of manganese ferrite nanoparticles

The growth kinetics of manganese ferrite (MnFe2O4) nanoparticles was studied by solvothermal reaction of iron and manganese salts in ethylene glycol as a solvent. To explore the mechanism of the nanoparticle formation and development, polyethylene glycol (PEG) with different molecular weights and polyvinyl pyrrolidone (PVP) were used as polymeric surfactants to investigate their effects on the formation of MnFe2O4 nanoparticles. The size evolution and the size distribution not only dependent on the kind of surfactant but also on the time and temperature of reaction process. In the presence of low molecular weight PEG (PEG300), nanoparticles with diameter of 180nm and narrow size distribution could be produced at 160°C during 12h of reaction while the nanoparticles with average size of 330nm were formed by using PEG300 at 200°C and 48h. Therefore, by increasing the temperature and the time of reaction, the size of nanoparticles was increased and finally reached a critical size and then collapsed. When a large molecular weight surfactant PEG10000 was used, the nanoparticles with average size of 230nm were formed at 180°C and 60h. In the case of PEG300 and PEG10000 as lower and higher molecular weights, the separation between building blocks occurred after 60h and 48h for 180°C and 200°C, respectively. However, more collapses between primary building blocks were observed by using PEG10000. The nanoparticles were composed of small building blocks and exhibited a spherical mesocrystal structure which was demonstrated from the TEM and scanning electron microscope (SEM) results. The investigation on the growth mechanism of the nanoparticles indicated that the formation of manganese ferrite was followed by the attachment and growth of primary building blocks and their Ostwald ripening process.