Preparation and analysis of multilayer composites based on polyelectrolyte complexes

A method for preparing multilayer film composites based on chitosan has been developed by the example of polymer pairs: chitosan–hyaluronic acid, chitosan–alginic acid, and chitosan–carrageenan. The structure of the composite films is characterized by X-ray diffractometry and scanning electron microscopy. It is shown that the deposition of a solution of hyaluronic acid, alginic acid, or carrageenan on a chitosan gel film leads to the formation of a polyelectrolyte complex layer at the interface, which is accompanied by the ordering of chitosan chains in the surface region; the microstructure of this layer depends on the nature of contacting polymer pairs.     

Low-Voltage Scanning Electron Microscopy and Energy-Dispersive X-Ray Microanalysis of the Interface of Multilayer Polymer Composite

The morphology of the layer of polyelectrolyte complex, which is formed in the composite based on chitosan and sulfoethyl cellulose during the contact of a solution of one of them with a gel film of the other one, has been investigated by the low-voltage (≤3 kV) scanning electron microscopy. A technique for eliminating the effects related to charge accumulation on the dielectric film surface is proposed.     

Seed-mediated synthesis of uniform ZnO nanorods in the presence of polyethylene glycol

Large quantities of ZnO nanorods have been synthesized by the seed-mediated method in the presence of polyethylene glycol at 90 °C. The products are characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and high-resolution transmission electron microscopy. The as-grown ZnO nanorods are uniform with a diameter of 40–70 nm and length about 2 μm. The nanorods grew along the [0 0 1] direction. Possible roles of ZnO seeds and polymer in the growth of ZnO nanorods are also discussed.     

Novel polymer–inorganic hybrid materials fabricated with in situ composition and luminescent properties

A new polymer–inorganic material was synthesized from terephthalic acid (TPA) and rare-earth ion (Tb³⁺, Eu³⁺) complex, which rare-earth ions connect with polymer by covalent bands. The luminescent europium and terbium coordination polymers, PET–Tb and PET–Eu, were produced in situ through low temperature solution polycondensation (PET = polyethyl terephthate ester). FTIR spectroscopy, ultraviolet absorption and scanning electron microscopy were applied to characterize the structure of obtained hybrid material. Phosphorescence and fluorescence spectra were applied to characterize the photophysical properties of the obtained hybrid material. The experimental result shows that the strong luminescence of rare-earth ions substantiates optimum energy match and effective intramolecular energy transfer between the triplet state energy of coordination complex and the emissive energy level of the rare-earth ions. The hybrid material systems can be expected to have potential applications in photophysical sensors.     

Conductivity,thermal and infrared studies on plasticized polymer electrolytes with carbon nanotubes as filler

New composite polymer electrolytes (CPE) are prepared using solution-casting technique. The CPE are based on polyethylene oxide (PEO) and employ lithium hexafluorate (LiPF₆) as the doping salt, ethylene carbonate (EC) as the plasticizer and amorphous carbon nanotubes (αCNTs) as the filler. The crystallinity and ionic conductivity of the CPE are examined in this work. The conductivity increases from 10^?10 to 10^?5 S cm^?1 upon the addition of salt. The incorporation of EC and αCNTs into the salted polymer enhances the conductivity significantly to 10^?4 and 10^?3 S cm^?1. The Vogel–Tamman–Fulcher (VTF) plots suggest that the temperature dependence of conductivity is a thermally activated process. Differential Scanning Calorimetry (DSC) studies show that the melting transition temperature and crystallinity decrease upon the addition of salt, EC and αCNTs into the polymer electrolyte system. The complexation, nature and concentration of the various ionic species are examined using Fourier Transform Infrared Spectroscopy (FTIR). Scanning electron microscopy (SEM) images show the changes in morphologies of the composite polymer electrolytes. The application of CPE especially in batteries and the advantages of this composite are highly conductive and stable at elevated temperature.     

Electron Microscopy Studies of Manuscripts from Russian National Library

Crystallography Reports - Inks of historical documents from the collection of the Russian National Library and model samples on paper and polymer were studied by transmission electron microscopy...     

Metastable SiCN glass matrices studied by energy-filtered electron diffraction pattern analysis

Bulk SiCN glasses, derived from polymer precursors with tailored architectures, were characterized upon pyrolysis at 1000 °C and subsequent annealing at 1400 °C and 1540 °C. The characterization tools employed were high-resolution transmission electron microscopy (HRTEM) imaging and energy-filtered selected area electron diffraction (EF-SAED). Main emphasis of this work was to verify as to whether the intrinsic amorphous structure of polymer-derived bulk materials exhibits different structural features upon pyrolysis, that depend on the functionalities of the pre-ceramic polymer, and whether such characteristic features are maintained upon high-temperature anneal. HRTEM imaging did not reveal any pronounced variation between the different SiCN glass structures after the organic–inorganic transition at 1000 °C or even upon heat treatment at 1400 °C. However, EF-SAED analysis showed differences in the amorphous structure of the four polymer-derived SiCN glasses studied even upon thermolysis at 1000 °C. The evolution of the electron diffraction intensity profiles of the EF-SAED patterns after subsequent thermal treatment at elevated temperatures showed clear evidence of structural rearrangements within the SiCN glass networks upon annealing at temperatures exceeding the pyrolysis temperature. The experimental results provide evidence that the metastable glass structure of polymer-derived SiCN ceramics depends on the starting polymer employed and, in addition, that the intrinsic glass architecture affects the thermal stability (onset of crystallization) of the amorphous matrix.     

Low temperature synthesis of spindle‐like ZnO nanostructures under microwave irradiation

A simple and general microwave route is developed to synthesize nanostructured ZnO using Zn(acac)₂·H₂O (acac = acetylacetonate) as a single source precursor. The reaction time has a great influence on the morphology of the ZnO nanostructures and an interesting spindle‐like nanostructure is obtained. The microstructure and morphology of the synthesized materials are investigated by X‐ray diffraction (XRD), scanning electron microscopy (SEM), field‐emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). It is found that all of them with hexagonal wurtzite phase are of single crystalline structure in nature. Ultraviolet–visible (UV‐vis) absorption spectra of these ZnO nanostructures are investigated and a possible formation mechanism for the spindle‐like ZnO nanostructures is also proposed.     

Effect of polymer matrix on structure of Se particles formed in aqueous solutions during redox process

Transmission electron microscopy and X-ray energy dispersive microanalysis study of the structure of particles formed during the reduction of Se(IV) to Se(0) in aqueous solutions in the presence of amphiphilic polymers showed the formation of Se/polymer composite particles. The content of carbon inside the particles can be as large as 80 at %. Polymers deeply influence the structure of particles. Depending on polymers, the composite particles may be unstable with time and they spontaneously evolve from Se/polymer composite particles to crystalline particles of monoclinic Se. For the stable ones, addition of bacterial cellulose Acetobacter xylinum gel-film can induce crystallization in the particles which expel the polymeric material. The Se/polymer composite particles and Se crystalline particles exhibit different sensitivity to electron irradiation and stiffness.     

Growth of calcium carbonate in polyacrylamide hydrogel: Investigation of the influence of polymer content

The growth of calcium carbonate crystals has attracted growing attention as a model system for biomineralisation processes. Organic molecules and gelatinous matrices are known to play an essential role in the formation of hard tissues. For the investigation of the function of specific influence factors, a model experiment is necessary. Several hydrogels were previously tested as growth matrices for calcium carbonate.

For laboratory experiments, a double diffusion set-up for the growth of crystals in gels was established earlier. Calcium carbonate crystals were grown in polyacrylamide hydrogels.

Here the influence of the polymer content in the hydrogels on the crystallisation behaviour is reported. Time-resolved and spatially resolved crystallisation experiments were conducted. The collected calcium carbonate precipitates were analysed by light microscopy, scanning electron microscopy and X-ray diffraction.

The morphology of the developing crystals was found to be dependent on the polymer content of the hydrogels.     

Phase formation and physical properties of mechanically alloyed amorphous 55Mg35Ni10Si

Amorphous 55Mg35Ni10Si alloy powder has been synthesized by mechanical alloying technique using pure Mg, Ni and Si elemental powders. The transformation of the crystalline powders into an amorphous one has been investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and differential scanning calorimetry. The new material produced has a higher thermal stability than reported results, which is beneficial to the fabrication of Mg–Ni–Si bulk amorphous components through powder metallurgy.     

One‐step green synthesis by organic molten salt method and optical properties of CdS nanosheets

Cadmium sulfide (CdS) nanosheets were synthesized by an environment friendly, “green” organic molten salt (OMS) method at 220 °C. The as‐synthesized products were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS), respectively. The XRD results reveal that the as‐synthesized CdS nanosheets are of the hexagonal wurtzite structure and the CdS nanosheets grow along the c‐axis. The SEM results indicate that the diameters and thickness of the CdS nanosheets are about 20–40 nm and 5–10 nm, respectively. The optical properties of the CdS nanosheets were investigated by ultraviolet–visible (UV‐Vis) spectroscopy and photoluminescence (PL) spectroscopy. The ultraviolet–visible spectrum exhibits two excitonic peaks with a step‐like absorption and the photoluminescence spectrum shows a green emission peak centered at around 524 nm. A possible growth mechanism of CdS nanosheets was discussed.     

Investigation of the structure of nanocrystalline refractory oxides by X-ray diffraction,electron microscopy,and atomic force microscopy

The structures of nanocrystalline fibrous powders of refractory oxides have been investigated by different methods: determination of coherent-scattering regions, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic-force microscopy (AFM). The sizes of nanograins of different crystalline phases of refractory metal oxides have been determined during the formation of these nanograins and the dynamics of their growth during heat treatment in the temperature range 600–1600°C has been studied. The data on the structure of nanocrystalline refractory oxide powders, obtained by different methods, are in good agreement. According to the data on coherent-scattering regions, the sizes of the ZrO₂ (Y₂O₃) and Al₂O₃ grains formed are in the range 4–6 nm, and the particle sizes determined according to the TEM and AFM data are in the ranges 5–7 and 2–10 nm, respectively. SEM analysis made it possible to investigate the dynamics of nanoparticle growth at temperatures above 1000°C and establish the limiting temperatures of their consolidation in fibers.

     

Polypyrrole/polyphosphate organic–inorganic nanocomposites

Polypyrrole/polyphosphate organic–inorganic nanocomposites were synthesized by a single-step synthesis in which the inorganic host network develops initially from a sol–gel transition and provide a restricted environment for pyrrole polymerization. The organic polymer forms, entrapped within the polyphosphate gel. The samples were characterized by UV–visible–NIR, infrared, Raman and electron paramagnetic resonance spectroscopies and thermogravimetric analysis. Self-standing thick films and powdered samples were obtained by adjusting the pyrrole and oxidant total amounts and their stoichiometric ratio. Self-standing samples in which the organic polymer is dispersed in nanosized domains within the inorganic matrix were prepared with up to a 10.8% polypyrrole load in its oxidized conducting form.     

Electron microscopy of phase and structural transformations in soft magnetic nanocrystalline Fe-Zr-N films

The effect of deposition conditions (film thickness) on the structure of soft magnetic Fe_80–78Zr₁₀N_10–12 films formed by reactive magnetron deposition on a heat-resistant glass substrate has been investigated by analytical transmission electron microscopy, high-resolution electron microscopy, and diffraction analysis. The processes of evolution of the phase and structural state of films and the film-substrate interface upon annealing in the temperature range of 200–650°C have been analyzed taking into account the thermodynamic, kinetic, and structural factors and the specific features of the nanocrystalline state.     

Kinetics of the thermally induced precursor curing to polymer via statistical analysis of TEM images

Thermally induced curing of the precursor to the cross-linked polymer was studied with transmission electron microscopy. The cured polymer was observed to have micro-domain morphology. Analysis of the microscopic images resulted in the statistical size distributions of micro-domains described subsequently using principles of irreversible thermodynamics. The statistical distribution parameters were determined to change with the curing temperature. A correlation of micro-structural and macroscopic parameters (the mean size of micro-domains and the dynamic Young’s modulus), both varying during the precursor curing, was found and explained in terms of the kinetic concept of fracture.     

Influence of Curing Frequency on the Morphology and the Electro-Optical Property of Polymer-Stabilized Cholesteric Textures

The effect of curing frequency on the morphology of polymer networks and the electro-optical property of normal-mode polymer-stabilized cholesteric textures (PSCTs) has been investigated. The scanning electron microscopy indicates that the shape of polymer networks transforms from honeycomb-like to fiber-like due to the increased solubility of the monomer at higher curing frequencies. The PSCTs cured at lower frequencies with sufficiently large network voids show a two-stage reorientation process that correlates with two kinds of cholesteric liquid crystal (LC) under different environments. The threshold voltage decreases as the curing frequency increases from 1 Hz to 10,000 Hz, while the field-off response time increases.     

Synthesis and characterization of mesoporous,tungsten-containing molecular sieve composites

Mesoporous, tungsten-containing molecular sieve (W-SBA-15) composites were successfully synthesized via one-step hydrothermal processing using tetraethyl orthosilicate (TEOS) as the silica precursor, sodium tungstate as the tungsten precursor, and pluronic P123 triblock polymer (EO₂₀PO₇₀EO₂₀, M_av = 5800) as a structure-directing reagent. The influence of various synthesis factors, such as TEOS/sodium tungstate (Si/W) molar ratios, stirring solution temperatures, TEOS pre-hydrolysis time, and crystallization temperatures, on the structure of the W-SBA-15 composite were investigated. The prepared materials were characterized by using X-ray diffraction (XRD), infrared spectroscopy (IR), diffuse reflectance ultraviolet–visible spectroscopy (DR UV–vis), scanning electron microscopy (SEM), and nitrogen adsorption–desorption measurements. The results showed that all the W-SBA-15 composite materials retained the mesopore structure of SBA-15 and the tungsten oxide species successfully substituted silica in the framework.     

Preparation of amorphous carbon nanotubes using attapulgite as template and furfuryl alcohol as carbon source

Amorphous carbon nanotubes were synthesized by vapor deposition polymerization (VDP) method using attapulgite as template and furfuryl alcohol as carbon source. The morphology and microstructure analysis of the as-prepared samples showed that highly pure amorphous carbon nanotubes were obtained, and determined by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SEAD) and energy dispersive X-ray (EDX) spectrum. The Brunauer–Emmett–Teller (BET) surface area analysis indicated that the specific surface area of the as-prepared amorphous carbon nanotubes reaches up to 503.1 m²/g. A hypothesis about the formation mechanism of the amorphous carbon nanotubes was also proposed accordingly.     

Cover Picture: Cryst. Res. Technol. 2/2010

The cover picture shows secondary electron microscopy (SEM) images of In2O3 nanocrystals. (see pages 173–177).