Preparation and characterization of pseudocubic hematite particles by utilizing polyethylene amine nonionic surfactants in forced hydrolysis reaction

The shape and porosity of hematite particles, produced from a forced hydrolysis reaction of acidic FeCl₃ solution, were controlled by using polyethylene amine nonionic surfactants (Surfonamine®; 0～10 wt.%). Surfonamine® possesses a nominal formula of CH₃-(PEO) _x -(PPO) _y -NH₂. Surfonamine with the highest total amine content (PEO contents were over 76 mol%, L-100) gave spherical particles, but those with lower total amine contents (L-200, L-207 and L-300) produced pseudocubic hematite particles. The pH value of the system with 10 wt.% of L-100 rose up to 8.49. With this pH rise, the diameter of the spherical particles was dramatically decreased. This fast particle formation was explained by the aggregation of very fine 6-line ferrihydrite particles produced at their high pH conditions. The uniformity of pseudocubic hematite particles produced with L-200, L-207 and L-300 were improved by increasing their concentrations. Since the pH values of these systems before aging were controlled between 2.03 and 2.35, it was presumed that the Surfonamine molecules acts as a buffer agent and attained pseudocubic particles. From the calculation of crystallite size, all the pseudocubic hematite particles were regarded as a polycrystal as well as the large spherical hematite particles produced without Surfonamine (control system). This polycrystallinity of the particles provided evidence that the particles are grown by aggregation of polynuclear (PN) primary particles. Not only the morphology but also the pore size of hematite particles was controlled from nonporous to microporous by using Surfonamines. The N₂ adsorption experiment and t-plot curve analysis revealed that the pseudocubic hematite particles have uniform micropores. The XRD, transmission electron microscope, inductively coupled plasma atomic emission spectroscopy and total organic carbon analysis measurements employed on the systems produced for pseudocubic particles elucidated that the pseudocubic crystal habit was formed by the specific adsorption of chloride ions and/or chloroferric complexes to the {012} faces, restraining the growth process through stacking of ultrafine PN particles in the direction of normal to the {012} faces but strictly restricting the growth and mutual fusion of PN ones. The uniform micropores could be produced between the PN particles. The uniform pseudocubic particles were found to be an effective photocatalytic material than the spherical particles due to their large size with uniform flat crystal faces.     

Control on the porosity of disk-like hematite particles prepared from a forced hydrolysis reaction using polyvinyl alcohol

The effects of polyvinyl alcohol (PVA) molecules on the porosity of disk-like hematite particles produced from the forced hydrolysis reaction using two kinds of PVA molecules with a well-defined molecular weight and a high degree of saponification (PVA-105 and PVA-124) were investigated. It is evident from TEM and field-emission scanning electron microscope (FE-SEM) measurements that a fraction of particles lost their spherical habit and acquired a disk-like shape by the addition of small amounts of both PVA molecules, though no difference in the particle size between the two PVA systems was observed. FE-SEM images of the particles revealed that the disk-like hematite particles are made up of small cluster particles with a diameter of approx. 5–10 nm. The disk-like particles produced a rather lower concentration for PVA-124 with a higher molecular weight than that for PVA-105 with a lower molecular weight. This fact was due to the large number of hydroxy groups in PVA-124 molecules than in PVA-105; hydroxy groups act as adsorption sites onto polynuclear (PN) primary particles and cause pronounced effects on the formation and structure of particles during the aggregation of PN particles. It was clarified from N₂ adsorption measurements at 77 K that the porosity of the hematite particles can be controlled from microporous to mesoporous by changing the concentrations of PVA-105 and PVA-124, as was classified into three groups, i.e., groups 1, 2, and 3. The control particles produced without PVA molecules, classified into group 1, showed type IV adsorption isotherms, and only the voids produced between spherical particles were detected as mesopores. On the other hand, the particles produced with small amounts of PVA produced micropores as classified in group 2. In this group, the particles produced uniform micropores after being outgassed at 100–200 °C. The hematite particles produced with high concentrations of PVAs were classified into group 3. In this group, the particles after being outgassed at lower temperature produced micropores with diameters between 0.6 and 2.0 nm, though the micropores in the particles changed to mesopores after outgassing at 300 °C. This mesopore formation was attributed to the elimination of the PVA-adsorbed layer by evacuation at 300 °C, i.e., the large voids residing in the disk-like hematite particles make the particles mesoporous. This mesopore formation was further confirmed by adsorption experiments of C₆H₆(benzene) and CCl₄ molecules at 298 K.     

Control on shape, porosity and surface hydrophilicity of hematite particles by using polymers

The shape, porosity, and surface hydrophilicity of hematite particles formed from a forced hydrolysis reaction of acidic FeCl₃ solution were controlled by using a trace of polymers (0.001 and 0.003 wt%). The spherical particles were produced on the systems with polyvinyl alcohol (PVA) and polyaspartic acid (PAS). In the case of polyacryl amide (PAAm), slightly small spherical particles were precipitated at 0.003 wt%. However, polyacrylic acid (PAAc) and poly-γ-glutamic acid (PGA) gave ellipsoidal particles. This morphological change on hematite particles depended on the order of functional groups of polymers as –OH<–CONH₂<–COOH<–COOH and ⟩C=O, corresponding to the order in extent of polymer molecules for complexation to Fe³⁺ ions and adsorption onto particle surface. Accompanying this order, the hematite particles produced were changed from less porous to microporous. On the other hand, only the system with 0.003 wt% of PAAm produced mesoporous hematite particles. Choosing the kinds of polymers also controlled the ultramicroporosity and surface hydrophilicity of the particles.     

Phase behavior,crystallization, and nanostructures in thermoset blends of epoxy resin and amphiphilic star‐shaped block copolymers

This article reports thermoset blends of bisphenol A‐type epoxy resin (ER) and two amphiphilic four‐arm star‐shaped diblock copolymers based on hydrophilic poly(ethylene oxide) (PEO) and hydrophobic poly(propylene oxide) (PPO). 4,4′‐Methylenedianiline (MDA) was used as a curing agent. The first star‐shaped diblock copolymer with 70 wt % ethylene oxide (EO), denoted as (PPO‐PEO)₄, consists of four PPO‐PEO diblock arms with PPO blocks attached on an ethylenediamine core; the second one with 40 wt % EO, denoted as (PEO‐PPO)₄, contains four PEO‐PPO diblock arms with PEO blocks attached on an ethylenediamine core. The phase behavior, crystallization, and nanoscale structures were investigated by differential scanning calorimetry, transmission electron microscopy, and small‐angle X‐ray scattering. It was found that the MDA‐cured ER/(PPO‐PEO)₄ blends are not macroscopically phase‐separated over the entire blend composition range. There exist, however, two microphases in the ER/(PPO‐PEO)₄ blends. The PPO blocks form a separated microphase, whereas the ER and the PEO blocks, which are miscible, form another microphase. The ER/(PPO‐PEO)₄ blends show composition‐dependent nanostructures on the order of 10?30 nm. The 80/20 ER/(PPO‐PEO)₄ blend displays spherical PPO micelles uniformly dispersed in a continuous ER‐rich matrix. The 60/40 ER/(PPO‐PEO)₄ blend displays a combined morphology of worm‐like micelles and spherical micelles with characteristic of a bicontinuous microphase structure. Macroscopic phase separation took place in the MDA‐cured ER/(PEO‐PPO)₄ blends. The MDA‐cured ER/(PEO‐PPO)₄ blends with (PEO‐PPO)₄ content up to 50 wt % exhibit phase‐separated structures on the order of 0.5–1 μm. This can be considered to be due to the different EO content and block sequence of the (PEO‐PPO)₄ copolymer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 975–985, 2006     

Preparation of mesoporous hematite particles by a forced hydrolysis reaction accompanying a peptide production reaction

The influence of carbodimide (CI), well known as a condensing agent for producing peptides from l-phenylalanine (l-Phe), on the formation of hematite (-Fe₂O₃) particles through a forced hydrolysis reaction of acidic FeCl₃ solution was examined. The large ellipsoidal particles were produced together with needle-like -FeOOH and fine Fe₃O₄ ones in the systems both with l-Phe and CI, though the system only with CI was not essentially changed the particle shape. CI produced the characteristic large ellipsoidal particle accompanying the production of peptides by condensing l-Phe. This behavior was explained by the adsorption of peptides on β-FeOOH and polynuclear (PN) particles; the adsorption of peptides retarded the phase transformation from β-FeOOH to hematite along with the heterogeneous aggregation of PNs, resulting the large ellipsoidal hematite particles. CI reduced Fe³⁺ to Fe²⁺ ions during aging the solution. The decomposition of urea, by-products of peptide formation, produced two kinds of amines to raise the solution pH and provided -FeOOH and Fe₃O₄ particles. The large ellipsoidal hematite particles exhibited large specific surface area and high mesoporosity by adsorption of peptides onto PN particles within the hematite particles. The morphology and inner structure of hematite particles were exceedingly altered by using a reaction of peptide production and this procedure is expected for a new developing method of high-quality porous materials.     

In-vivo fluorescence imaging technique using colloid solution of multiple quantum dots/silica/poly(ethylene glycol) nanoparticles

This paper describes a method for producing silica particles containing multiple quantum dots (QD/SiO₂), a method for surface-modifying the particles with poly(ethylene glycol) (QD/SiO₂/PEG), and an in vivo fluorescence imaging technique using colloid solution of the QD/SiO₂/PEG particles. The QDs used were ZnS-coated CdSe_xTe_1?x nanoparticles surface-modified with carboxyl groups, and had an average size of 10.3 ± 2.1 nm. The QD/SiO₂ particles were fabricated by performing sol–gel reaction of tetraethyl orthosilicate using NaOH as a catalyst in the presence of the QDs. The produced particles formed core–shell structure composed of multiple QDs and silica shell, and had an average size of 50.2 ± 17.9 nm. Surface-modification of the QD/SiO₂ particles with PEG, or PEGylation of the particle surface, was performed by using methoxy polyethylene glycol silane. Fluorescence of QD colloid solution was not quenched even through the silica-coating and the PEGylation. Tissues of a mouse could be imaged by injecting the concentrated colloid solution into it and measuring fluorescence intensity emitted from the tissues.     

Control of properties of nanocomposites bio-based collagen and cellulose nanocrystals

Collagen is an important biomaterial because it has many applications in the biomedical sector. However, the high hydrophilicity of collagen (COL) leads to easy swelling. Thus, controlling this property is highly desirable. In this work, cellulose nanocrystals (CNCs) dispersed in glycerol (GLI) were incorporated in the matrix collagen to tailor the hydrophilicity and mechanical properties. Study of the hydrophilicity of the bio-based nanocomposite was evaluated by contact angle measurement and thermogravimetric analysis. Mechanical analyses showed that CNCs are excellent reinforcing fillers to the collagen matrix. Synchrotron small-angle X-ray scattering was employed to investigate the nanostructures of COL/GLI/CNC nanocomposites and CNC water dispersion. CNC in concentrations up to 1 wt% presents an intermediate shape between a rod and a plane with a 9.34-nm radius of gyration (R _g). Bio-based nanocomposites present two different structural levels with two types of particles with very different R _gs. At the intermediate power-law regime, a large-scale mass fractal aggregate is observed. In the high-power-law regime, it is observed scattering from primary particles smaller than 1 nm. As the CNC concentration increases, the original particle distorts from a rod to a plate. The cytotoxicity assay indicates that the collagen and nanocomposites did not affect the cell viability of rat calvarial cells in vitro.     

Thermoresponsive submicron-sized core–shell hydrogel particles with encapsulated olive oil

Thermoresponsive submicron-sized core–shell hydrogel particles with incorporated olive oil were synthesised and studied. The microspheres having poly(N-isopropylacrylamide-co-methyl methacrylate) core and poly(N-isopropylacrylamide) shell were synthesised by emulsifier-free seed polymerisation method. The morphology, particle size and distribution characteristics of the core microspheres were studied with different amount of initiator, monomer–solvent ratio and polymerisation time using scanning electron microscopy and dynamic light scattering particle size analysis. The prepared core and core–shell microspheres were regularly spherical with average size of around 190.0 and 320.0 nm respectively and nearly monodispersed size distribution. Transmission electron microscopy study revealed the core–shell structure of the microspheres. The thermoresponsive transition temperature (T _t) of the core–shell microspheres was determined as 33 °C by optical absorbance measurement, dynamic light scattering particle size analysis and differential scanning calorimetry. The release rate of olive oil from core–shell microspheres was accelerated by squeezing out the entrapped olive oil as the temperature was increased above T _t. Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy study indicated the formation of copolymer.     

The influence of concentration of doping elements on anatase–rutile transformation at the synthesis of rutile pigments (Ti,Cr,Nb)O2 and their pigmentary properties

An analysis of the effects of dopants concentration and different starting titanium compounds on the anatase to rutile phase transformation at the synthesis of rutile pigments Ti_1?3xCr_xNb_2xO_2±δ is presented in this study. The main goal was to analyze reaction mixtures for x = 0.05 (previous study) and 0.30 by simultaneous TG–DTA analysis and to determine the temperature of anatase–rutile transition. For x = 0.05, initial temperatures 760–830 °C are needful for a formation of rutile structure. The temperature is the lowest for the hydrated Na₂Ti₄O₉ paste (760 °C) and similar for other starting compounds of titanium. But for x = 0.30, the anatase–rutile transition begins at higher temperatures 910–1,030 °C because of high-Nb content, which is the inhibitor of this modification change. In addition, we found the influence of calcination temperatures (850, 900, 950, 1000, 1050, 1100, and 1150 °C) on color properties and particle size distribution of these materials prepared from anatase TiO₂ and with x = 0.30. Selected pigments were also analyzed by X-ray powder diffraction.     

Synthesis and characterization of Ti(IV)-substituted calcium hydroxyapatite particles by forced hydrolysis of Ca(OH)2-Na5P3O10-TiCl4 mixed solution

Ti(IV)-substituted calcium hydroxyapatite (TiHap) particles were prepared by aging Ca(OH)₂, TiCl₄, and sodium triphosphate (sodium tripolyphosphate, Natpp: Na₅P₃O₁₀) mixed solution at 100 °C for 18 h. The ellipsoidal secondary TiHap particles with ca. 100～150 nm in length composing by aggregation of small ellipsoidal primary particles with ca. 20 nm in length were produced at atomic ratio of Ti/(Ca+Ti) [X_Ti]≦0.2. The in situ IR spectra of these TiHap particles exhibited very small bulk OH^? band at 3,570 cm^?1. This result indicated that the TiHap particles were formed by aggregation of fine primary particles and OH^? ions along with c-axis in the primary particles were disordered. The TiHap particles with Ca/P atomic ratio larger than theoretical value of 1.67 did not exhibit surface P–OH groups at 3,659 and 3,682 cm^?1. The diffuse reflectance UV spectra of TiHap particles revealed that these particles have a UV absorption property, especially fabricated at X_Ti?=?0.1. The particles prepared at X_Ti?=?0.6 and 0.8 were amorphous and nanoparticles with 5～10 nm in diameter, but those precipitated at X_Ti?=?1.0 were poorly crystallized anataze-type TiO₂ nanoparticles.     

Visible light activated catalytic effect of iron containing soda-lime silicate glass characterized by 57Fe-Mössbauer spectroscopy

A relationship between local structure and visible light activated catalytic effect of iron containing soda lime silicate glass with the composition of 15Na₂O·15CaO·xFe₂O₃·(70-x)SiO₂, x = 5–50 mass %, abbreviated as NCFSx was investigated by means of ⁵⁷Fe-Mössbauer spectroscopy, X-ray diffractometry (XRD), small angle X-ray scattering (SAXS), electrospray ionization mass spectrometry (ESI–MS) and ultraviolet–visible light absorption spectroscopy (UV–Vis). Mössbauer spectra of NCFSx glass with ‘x’ being equal to or larger than 30 after isothermal annealing at 1,000 °C for 100 min consisted of a paramagnetic doublet and a magnetic sextet. The former had isomer shift (δ) of 0.24 mm s^?1 and quadrupole splitting (Δ) of 0.99 mm s^?1 due to distorted Fe^IIIO₄ tetrahedra, and the latter had δ of 0.36 mm s^?1 and internal magnetic field (H _int) of 51.8 T due to hematite (α-Fe₂O₃). The absorption area (A) of α-Fe₂O₃ varied from 47.2 to 75.9, 93.1, 64.8 and 47.9 % with ‘x’ from 30 to 35, 40, 45 and 50, indicating that the amount of precipitated α-Fe₂O₃ varied with the Fe₂O₃ content of NCFSx glass. The precipitation of α-Fe₂O₃ was also confirmed by XRD study of annealed NCFS glass with ‘x’ larger than 30. A relaxed sexted with δ, H _int and Γ of 0.34 mm s^?1 and 37.9 T and 1.32 mm s^?1 was observed from the Mössbauer spectra of annealed NCFSx glass with ‘x’ of 45 and 50, implying that the precipitation of non-stoichiometric iron hydroxide oxide with the composition of Fe_1.833(OH)_0.5O_2.5 having the similar structure of α-Fe₂O₃ and α-FeOOH. A remarkable decrease in the concentration of methylene blue (MB) from 10 to 0.0 μmol L^?1 with the first-order rate constant (k) of 2.87 × 10^?2 h^?1 was observed for 10-day leaching test using annealed NCFS50 glass under visible light irradiation. ESI–MS study indicated that existence of fragments with m/z value of 129, 117 and 207 etc. originating from MB having m/z of 284. This result evidently showed that the MB concentration decreased due to visible light induced decomposition caused by the visible light activated catalytic effect of α-Fe₂O₃ and/or Fe_1.833(OH)_0.5O_2.5 precipitated in soda-lime silicate glass matrix.     

Effects of amino acids on the formation of hematite particles in a forced hydrolysis reaction

The influence of amino acids on the formation of hematite particles from a forced hydrolysis reaction of acidic FeCl3 solution was examined. The spherical particles were produced on the systems with L-phenylalanine (L-Phe), L-serine (L-Ser) and L-alanine (L-Ala), though L-glutamine (L-Gln) and L-glutamic acid (L-Glu) gave ellipsoidal hematite particles. This morphological change in hematite particles is consistent with the order of stability constant of amino acids against to Fe3+ ions (K). The hematite particles produced with L-Glu, L-Gln and L-Ser were highly porous because they are formed by aggregation of cluster particles. These particles exhibited microporous behavior by outgassing the particles below 200 degrees C while they changed to mesoporous after treating above 300 degrees C by elimination of amino acids molecules remained between the cluster particles within the hematite particles. The hematite particles strongly depended on the nature of amino acids such as alternation of solution pH and adsorption affinity to beta-FeOOH and/or polynuclear primary (PN) particles. The systems on L-Ala and L-Phe, showing very rapid phase transformation from beta-FeOOH to hematite, exhibited the Ostwald ripening. A rotational particle preparation procedure suggested that the morphology of hematite particle is governed by the mode and strength of amino acid adsorption onto beta-FeOOH and/or PN particles.     

Sol–gel synthesis of nanocrystalline Zn1−xNixFe2O4 ceramics and its structural,magnetic and dielectric properties

Zn_1?xNi_xFe₂O₄ (0.0 ≤ x ≤ 1.0) nanoparticles are prepared by sol–gel method using urea as a neutralizing agent. The evaluation of XRD patterns and TEM images indicated fine particle nature. The average crystallite size increased from 10 to 24 nm, whereas lattice parameters and density decreased with increasing Ni content (x). Infrared spectra showed characteristic features of spinel structure along with a strong influence of compositional variation. Magnetic measurements reveal a maximum saturation magnetization for Zn_0.5Ni_0.5Fe₂O₄ (x = 0.5); however, reduced value of magnetization is attributed to the canted spin structure and weakening of Fe³⁺(A)–Fe³⁺(B) interactions at the surface of the nanoparticles. Impedance analysis for different electro-active regions are carried out at room temperature with Ni substitution. The existence of different relaxations associated with grain, grain boundaries and electrode effects are discussed with composition. It is suggested that x = 0.5 is an optimal composition in Zn_1?xNi_xFe₂O₄ system with moderate magnetization, colossal resistivity and high value of dielectric constant at low frequency for their possible usage in field sensor applications.     

Synthesis and characterization of thermoresponsive amphiphilic block copolymers incorporating a poly(ethylene oxide‐stat‐propylene oxide) block

Amphiphilic BuO‐(PEO‐stat‐PPO)‐block‐PLA‐OH diblock and MeO‐PEO‐block‐(PEO‐stat‐PPO)‐block‐PLA‐OH triblock copolymers incorporating thermoresponsive poly(ethylene oxide‐stat‐propylene oxide) (PEO‐stat‐PPO) blocks were prepared by ring‐opening polymerization of lactide (LA) initiated by macroinitiators formed from treating BuO‐(PEO‐stat‐PPO)‐OH and MeO‐PEO‐block‐(PEO‐stat‐PPO)‐OH with AlEt₃. MeO‐PEO‐block‐(PEO‐stat‐PPO)‐OH was prepared by coupling MeO‐PEO‐OH and HO‐(PEO‐stat‐PPO)‐OH, followed by chromatographic purification. The cloud points of 0.2% aqueous solutions are between 36 and 46 °C for the diblock copolymers that contain a 50 wt % EO thermoresponsive block and 78 °C for the triblock copolymer that contains a 75 wt % EO thermoresponsive block. Variable temperature ¹H NMR spectra recorded on D₂O solutions of the diblock copolymers display no PLA resonances below the cloud point and fairly sharp PLA resonances above the cloud point, suggesting that desolvation of the thermoresponsive block increases the miscibility of the two blocks. Preliminary characterization of the micelles formed in aqueous solutions of BuO‐(PEO‐stat‐PPO)‐block‐PLA‐OH conducted using laser scanning confocal microscopy and pulsed gradient spin echo NMR point to significant changes in the size of the micellar aggregates as a function of temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5156–5167, 2005     

The search for a solid electrolyte,as a polysulfide barrier,for lithium/sulfur batteries

Composite Li₁₀SnP₂S₁₂ (LSPS)/polyethylene oxide (PEO) films, containing 25 to 50 % polymer, were electrophoretically deposited from acetone-based suspension and tested as possible candidates for polysulfide barriers in Li/S batteries. It was found by XRD and XPS tests that saturation of composite films by LiI salt, followed by prolonged annealing at 90 °C, diminishes the crystallinity of neat LSPS and results in the formation of a novel composite Li_10+xI_xSnP₂S₁₂ (LISPS)/P(EO)₃/LiI solid electrolyte (x < 1). The high room-temperature ion conductivity of amorphous sulfide Li_10+xI_xSnP₂S₁₂ (0.1–0.3 mS cm^?1) is restricted by slow ion transport via the polymer electrolyte (PE) imbedded in ceramics and grain boundaries between the PE and sulfide. Increase in polymer content and temperature improves total ion transport in the LISPS/PEO system. Conformal EPD coating of sulfur and lithium sulfide cathodes by the developed composite electrolyte increased the reversible capacity and Faradaic efficiency of the Li/S and Li/Li₂S cells and enabled their operation at 60 °C.     

Preparation of La0.67Ca0.33MnO3:Ag x polycrystalline by sol–gel method

La_0.67Ca_0.33MnO₃:mol%Ag _x (LCMO:Ag _x , x = 0, 0.04, 0.08, 0.10 and 0.20) ceramics were prepared by sol–gel method. The X-ray diffraction studies of the LCMO:Ag _x samples confirm the pure phase of the LCMO composites with Pbnm space group. With the increase of Ag doping from x = 0 to 0.20, the normalized resistivity (ρ/ρ _300K ) of the samples around the metal–insulator transition temperature (T _p ) reduced in sequence. Both T _p and the peak of temperature coefficient of resistance (T _k ) improved 5–8 K. Energy dispersive X-ray spectroscopy analysis showed that the composition of La, Ca and Mn of the obtained LCMO composites was in accordance with the composition of the precursor. The results indicated that the improvement of grain boundaries and crystallization were responsible for the enhancements of ρ, T _p and T _k of LCMO:Ag _x composites. The fitted curves of electrical resistivity for LCMO:Ag _x composites indicated that the mechanisms of grain/domain boundary, electron–electron and magnon scattering and adiabatic small polaron hopping are proposed to explain the phase transition of ferro-magnetic metallic region (T < T _p ) and the para-magnetic insulating region (T > T _p ), respectively.     

Synthesis of VO2 Nanopowders. Part II. Hydrolysis of Vanadium Alkoxide/Citric Acid Premixes: VO2 Nanostructures of Controlled Shape

Reaction of VO(OiPr)₃/citric acid premixes with excess water produces stable, blue dispersions of V_xO_y gel nanoparticles (5–100 nm in diameter) that can be isolated via acetone precipitation. Annealing under reducing conditions transforms these gel particles into crystalline, faceted VO₂ nanoparticles of similar size. Larger V_xO_y gel particles (75–200 nm in diameter) form when V_xO_y nanogel dispersions are aged with aqueous ammonia. Upon annealing, these larger gel particles transform into crystalline VO₂ rods of 50 nm–10 μm in length. Hysteresis loops confirming a semiconductor-to-metal phase transition near 68 °C expected for crystalline VO₂ particles are recorded by variable-temperature electrical resistance and powder X-ray diffraction measurements.     

Structural relaxation of PbO–WO3–P2O5 glasses

The structural relaxation of three compositional series of PbO–WO₃–P₂O₅ glasses with composition (0.5 ? x/2)PbO·xWO₃·(0.5 ? x/2)P₂O₅, x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5; 0.5PbO·xWO₃·(0.5 ? x)P₂O₅, x = 0, 0.1, 0.2, and 0.3; and (0.5 ? x)PbO·xWO₃·0.5P₂O₅, x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 was studied by thermomechanical analysis. The structural relaxation was studied in the transformation region using the Tool–Narayanaswamy–Moynihan’s and Tool–Narayanaswamy–Mazurin’s models. The relaxation function of Kohlrausch Williams and Watts was used. The parameters of both models were calculated by nonlinear regression analysis of thermodilatometric curves measured by thermomechanical analyzer under the constant load. Both models very well describe the experimental data. It was found that the modulus is increasing with increasing amount of WO₃ in all glasses. On the contrary, the width of the spectrum of relaxation times is decreasing with increasing amount of WO₃ in all studied glasses. Both models possess the values of metastable melt thermal expansion coefficient equal to their experimental value.     

Microstructure and dielectric properties of Nd doped CaCu3Ti4O12 synthesized by sol–gel method

Ca_(1?3x/2)Nd _x Cu₃Ti₄O₁₂ (x = 0, 0.1, 0.2 and 0.3) powders and ceramics were prepared by sol–gel method. Effect of Nd on microstructure and dielectric properties were investigated. XRD patterns suggest that pure perovskite-like CCTO phase were obtained after calcining at 800 °C for 2 h. SEM pictures reveal that particle size monotonously decreases from 250 to 120 nm with increase of Nd concentration. The lattice parameters show an increasing trend with the enhancing amount of Nd³⁺ substitution. The average grain size of CCTO ceramics decrease from 2.0 to 0.8 μm with increase in Nd doping, which indicates that high concentration of Nd inhibits grain growth of CaCu₃Ti₄O₁₂. Both of the dielectric constant and dielectric loss decrease with increase in Nd concentrations. Ca_(1?3x/2)Nd _x Cu₃Ti₄O₁₂ ceramics with x = 0.3 shows the lowest dielectric constant of 1.12 × 10⁴ as well as the lowest dielectric loss value of 0.12 at 20 °C(10 kHz).     

Thermodynamics of formation of β-cyclodextrin inclusion complexes with four series of surfactant homologs

We report on a titration microcalorimetric study of the formation of β-cyclodextrin inclusion complexes with the members of series of anionic, cationic, and nonionic surfactant homologs containing even numbers of carbon atoms in the alkyl chains. n-Alkyltrimethylammonium bromides (C_xTAB, x = 6–16), sodium n-alkyl sulfates (SC_xS, x = 6–12), sodium n-alkanesulfonates (SC_xSN, x = 6–12), and N,N-dimethylalkylamine-N-oxides (DC_xAO, x = 8–12) were selected for use. The stoichiometry, the binding constant, and the changes in enthalpy, entropy, and Gibbs free energy of the complexation reactions were determined at 298 K. It was found in each case that the complexation is favored by both the enthalpy and the entropy changes and that the thermodynamics of the process is affected far more strongly by the length of the alkyl chain than by the nature of the headgroup.