Changes in the structural parameters and molecular dynamics of polyhydroxybutyrate-chitosan mixed compositions under external influences

Differential scanning calorimetry (DSC), EPR probe analysis, large-angle X-ray diffraction (XRD), and UV spectroscopy are used to study the molecular dynamics and structure of hydroxybutyrate (PHB) copolymer, chitosan, and mixed compositions thereof upon thermal treatment in an aquatic medium. It is shown that, in mixed compositions, starting from 30% PHB, the correlation time increases by an order of magnitude, indicative of a sharp slowdown of the molecular mobility of the probe, and, concurrently, the degree of crystallinity decreases abruptly, as evidenced by DSC and XRD analyses. The diffusion coefficient of rifampicin in mixed compositions also decreases with increasing PHB content. A short-term (1 h) thermal treatment (at 70°C) in water results in an increase in the molecular mobility of the probe in the system. Crystallinity changes in complex ways.     

Poly(3-Hydroxybutyrate) Matrices Modified with Iron(III) Complexes with Tetraphenylporphyrin. Analysis of the Structural Dynamic Parameters

The effect of small additions of the iron(III) complex with tetraphenylporphyrin (0–5%) on the structure and properties of ultrathin fibers based on poly(3-hydroxybutyrate) (PHB) was studied by differential scanning calorimetry (DSC), X-ray diffraction analysis (XRD), EPR probe method, and scanning electron microscopy. When tetramethylporphyrin was added to the PHB fibers, the crystallinity significantly increased, and the molecular mobility in the amorphous regions of the polymer decreased. The thermal treatment of the fibers (annealing at 140°C) led to significantly increased crystallinity and decreased molecular mobility in the amorphous regions of the PHB fibers. The addition of tetramethylporphyrin to the PHB fibers led to a sharp decrease in crystallinity. Ozonolysis of the fibers at small treatment times caused a considerable decrease in their molecular mobility (to 5 h), while prolonged ozonolysis led to increased mobility. The obtained fibrous materials have bactericidal properties and will find use in the development of antibacterial and antitumor therapeutic systems.     

Influence of the solvent on the segmental dynamics and structure in mixed compositions of polyurethane and styrene-acrylonitrile copolymer

The effect of the tetrahydrofuran (THF), methyl ethyl ketone (MEK), ethyl acetate (EA), and acetone (A) solvents on the structure and segmental dynamics of polyurethane (PU)-(styrene-acrylonitrile) (SAN) mixed compositions are studied by spin-probe EPR spectroscopy, differential scanning calorimetry, and infrared spectroscopy. The molecular mobility τ, the degree of crystallinity χ, the modulus of elasticity E alter only slightly in passing from 100% PU to a 50% PU-50% SAN, but the structural and dynamic properties change abruptly at a high SAN content in the composition, regardless of the type of solvent. The values of τ, χ, and elastic modulus for the mixed compositions increases depending on the type of solvent in the following sequence: THF, MEK, EA, A, which can be explained by the thermodynamic affinity between the solvent and solute. It is also shown that, with growing content of SAN in the composition, the number of intermolecular hydrogen bonds between nitrile and urethane groups (3344-cm^?1 band) increases.     

X-ray diffraction study of temperature dependence of Nairit polychloroprene permolecular structure

With use of the X-ray technique the permolecular structure of Nairit polychloroprene has been investigated. It is shown that the relative degree of crystallinity decreases with the increase in the polymerization temperature. At relatively low temperatures (18–30°C), in Nairits intensive formation of nuclei occurs and simultaneously existing crystallites collapse. Although mean sizes of crystallites decrease, the degree of crystallinity increases. At higher temperatures (above 30°C) melting of existing crystallites and decrease in the number of nuclei lead to decrease in crystallinity and mean sizes of crystallites.     

Effect of external influences on the structural and dynamic parameters of medicinal copolymers

ESR spectroscopy, DSC, IR spectroscopy are used to study the molecular dynamics, mechanical properties, the ability to ozone oxidation of ethylene-propylene copolymer (SEPE) and a copolymer of ether and urethane groups (SPEU). The behavior of the copolymers under tensile stress changes dramatically upon addition of > 5% ethylene units to polypropylene. Reversible deformation of oriented copolymers containing <5% ethylene units is accompanied by an increase in molecular mobility, with the opposite tendency being observed at a higher content of ethylene units. The sorption properties change in parallel with the molecular mobility. Samples containing >5% ethylene units turn out to be less resistant to ozone oxidation. Upon deformation of isotropic and weakly oriented SPEU sample, molecular mobility increases at the initial stage of stretching, decreasing throughout the strain range covered. Ozone oxidation, both in the loaded and unloaded states leads to an increase in the rigidity of SPEU chains, which manifests itself in the growth of the modulus of elasticity, correlation time, and activation energy. Thermal annealing in water also increases the rigidity of SPEU molecules.     

Influence of the Solvent on the Formation of CNR/BNR Polymer Blends

Structural dynamic analysis combining IR spectroscopy, DSC, and EPR spectroscopy is applied to studying films based on chlorinated natural rubber (CNR), butadiene nitrile rubber (BNR), and blends thereof. The influence of various solvents, such as methyl ethyl ketone (MEK), ethyl acetate (EA), methyl acetate (MA), and acetone (A), on the structure and molecular dynamics (τ) of CNR/BNR polymer films is examined. The strongest changes in the molecular mobility (τ) and the glass transition temperature (T_gt) relative to those of the starting materials are observed for the 50: 50% CNR/BNR blends prepared using all the solvents (except for acetone, the maximum values of τ for which is observed at a ratio of CNR: BNR = 80: 20%), which can be explained by the inversion of phases in the blends. Annealing at 140°С causes an increase in the correlation time of the probe, and, consequently, a decrease in the molecular mobility, which is due to the intermolecular crosslinking of the components.     

Oxidation of dodecane on vanadium-molybdenum catalysts

The catalytic oxidation of dodecane with air oxygen on individual and mixed vanadium-molybdenum (1 ? x)V₂O₅ · xMoO₃ oxide is studied over a temperature range of 250 to 400°C. It is shown that oxidation of dodecane to organic acids at 250°C produces undecylic acid C₁₁H₂₆COOH and carbon oxides, as products of the subsequent oxidation of formic acid. The most effective catalyst is a mixed oxide containing 75 mol % MoO₃ and 25 mol % V₂O₅. At 275–300°C, this catalyst provides the maximum yield of acids and a relatively low fraction of complete-oxidation products. Above 250°C, a mixture of acids and carbon oxides is formed, the yield of which increases with the temperature up to 300°C. As the temperature is increased still further, the yield of acids decreases due to their subsequent oxidation. The catalytic oxidation is accompanied by changes in the phase composition, morphology, and degree of crystallinity of the mixed-oxide catalysts. A possible mechanism of the catalytic process is considered.     

Structural phase transformations in annealed cubic ZnS nanocrystals

The structural changes of cubic ZnS (cZnS) nanocrystals (NCs) doped with 0.2 at.% Mn²⁺ pulse annealed in vacuum and in air, up to 500 °C, were investigated by multifrequency electron paramagnetic resonance (EPR), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The samples, prepared by a surfactant (Tween20)-assisted liquid–liquid reaction at pH = 6, consist of NCs with a tight size distribution around 3 nm and high crystallinity self-assembled into a stable mesoporous structure. The EPR spectra of the as prepared samples contain only the characteristic lines of the substitutional Mn²⁺(I) centers. No spectra from Mn²⁺ ions localized in (hydro)oxidized regions of the NCs surface were observed. The absence of such a surface layer could explain the stability of the cubic (sphalerite) structure observed by XRD and TEM in the investigated cZnS:Mn NCs annealed in vacuum up to 500 °C. The observation of the cubic-hexagonal transformation for the same NCs annealed in air supports the role of such layer in promoting this structural transformation. The narrowing of the EPR spectral lines above 200 °C with the increase in the average size of the cZnS:Mn crystallites was observed. The effect was more pronounced for the sample annealed in air. EPR also revealed the formation of minute amounts of substitutional Mn²⁺-type centers in a hexagonal ZnO structure at T ~ 300 °C, corresponding to the early stages of the thermally induced oxidation of the cZnS:Mn NCs.     

Low-temperature hydrothermal synthesis of highly photoactive mesoporous spherical TiO2 nanocrystalline

TiO₂ microspheres with mesoporous textural microstructures and high photocatalytic activity were prepared by hydrothermal treatment of mixed solution of titanium sulfate and urea with designed time. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N₂ adsorption-desorption measurements. The photocatalytic activity was evaluated via the photocatalytic oxidation of acetone in air at room temperature. The results show that the hydrothermal time significantly influences on the morphology, microstructure and photocatalytic activity of the as-prepared samples. With increasing hydrothermal time, specific surface areas and pore volumes decrease, contrarily, the crystallite size and relative anatase crystallinity increase. The photocatalytic efficiency of the as-prepared samples is obviously higher than that of commercial Degussa P25 (P25) powders. Especially, the as-prepared TiO₂ powders by hydrothermal treatment for 7 h shows the highest photocatalytic activity, which exceeds that of P25 by a factor of more than 2 times.     

Sonochemical synthesis of zeolite NaP from clinoptilolite

In the present work, natural clinoptilolite was converted to zeolite NaP using ultrasonic energy, in which the transformation time shortened remarkably. The effect of post-synthesis treatment using conventional hydrothermal was also investigated. The synthesized powders were characterized by XRD, TGA/DTA, SEM, and PSD analysis. The results showed that, increasing the sonication time (energy) has no significant effect on the product’s morphology. The crystallinity of the synthesized samples increased slightly with increasing sonication time, but their yield remained relatively unchanged. Furthermore, post-synthesis hydrothermal treatment showed very little influence on properties of the final product. Because the ultrasonic irradiation creates acoustic cavitation cracks on the surface structure of clinoptilolite particulates and increases the concentration of soluble alumino-silicate species, which favors the prevailing super-saturation, crystallization and crystal growth of zeolite NaP happen faster. The particles of zeolite NaP synthesized by ultrasonic irradiation consist of small crystallites of uniform size.     

Spin probe ESR studies of PEGxLiClO4 polymer electrolyte systems

The technique of Electron Spin Resonance (ESR) is shown to be useful in the study of dynamics of solid polymer electrolytes (SPE). Through the ESR of the nitroxide radical (2,2,6,6-tetramethyl-1-piperidine-1-oxyl; TEMPO) dispersed in the SPE PEG₄₆LiClO₄ temperature dependence of correlation time is found. The glass transition temperature T_g is estimated to be −51 °C from the measurement of T_50G, the temperature at which the extrema separation 2A_ZZ becomes 50G and is found to be close to that measured using DSC (−51.7 °C). T_g for pure PEG-2000, which could not be measured from DSC because of its high crystallinity, is determined to be −72 °C by spin probe ESR. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Microstructural study of different LDH morphologies obtained via different synthesis routes

In order to better understand the relationship between LDH synthesis parameters and their particle sizes, diverse carbonate intercalated NiAl-LDH phases were prepared using different coprecipitation conditions and their structure, microstructure and morphology were characterized. The samples were synthesized by coprecipitation either at constant pH, in strong alkaline medium or using urea decomposition. The influence of a post-synthesis hydrothermal treatment was also investigated. A well crystalline NiAl-CO₃ phase but containing a high stacking fault density was obtained by combining a strong basic medium and hydrothermal treatment at 120 °C for 24 h. Interestingly, the hydrothermal treatment increases the crystallinity of the samples but does not eliminate stacking faults. The crystallite sizes determined by modeling X-ray diffraction peak broadening with linear combinations of spherical harmonics are fully consistent with TEM observations confirming the validity of the approach used and indicating that the particles are probably small single crystals.     

DC conductivity and dielectric properties of maize starch/methylcellulose blend films

The transient current, electrical conductivity, dielectric constant (ε′), and dielectric loss factor (ε″) of starch and methylcellulose homopolymers and their blends with various compositions were studied under different conditions. The x-ray diffraction pattern was obtained for individual polymers and 50:50 wt/wt% blend sample to identify both the structure and degree of crystallinity. From transient current, the ionic and electronic transfer number as well as charge carrier density and drift mobility were determined. The values of activation energy in the temperature range 30–90 °C indicate that the conduction mechanism is due to combined electronic and ionic processes, while in the temperature range 100–160 °C, electronic contribution is predominant. The complex dielectric data of the present samples in an extended frequency and temperature range appear as different relaxation processes, which are connected with polymer dynamics.     

The physicochemical characteristics of oxidized polysaccharides

The paper presents the results obtained in studies of the physicochemical characteristics of modified polysaccharides prepared by the catalytic oxidation of starch with molecular oxygen in an alkaline medium. The amorphous-crystalline structure of starch was partially retained after oxidation. The differential scanning calorimetry data were used to determine the specific heat capacity of oxidized polysaccharides in the vitreous state over the temperature range 10–160°C and the enthalpy and temperature characteristics of fusion of amorphous-crystalline lamellae. The structural and thermodynamic parameters of crystallites (surface free energy, enthalpy, and entropy) were calculated. The segmental mobility of oxidized polysaccharide macromolecules and the transition from the vitreous to high-elasticity state were observed at T _g = 187.7°C, and the transition to the viscous-flow state, above 209°C. The pyrolysis of the polymer began after the unfreezing of its segmental mobility and was accompanied by the release of water and carbon dioxide and the formation of a large amount of coke foam.     

THERMAL CHARACTERIZATIONS OF WOOD FLOUR/STARCH CELLULOSE ACETATE COMPOUNDS

Thermogravity analysis (TGA) and differential scanning calorimetric (DSC) analysis, as well as dynamic thermal analysis (DMA), were carried out to study the interfacial interaction between wood flour (WF) and starch/cellulose acetate (SCA) blend. It was found that the main components in the compounds, namely, starch, cellulose, and cellulose acetate, started to decompose at around 330°C, a characteristic temperature for breaking glycoside-linked glucose units. Complexation of lignin in WF with amylose in SCA occurred during compounding, which gave rise to new crystallites that have a melting point of around 160°C. Hydrogen bonding is believed to play a key role in the crystallization. With increasing WF content, both the glass transition temperature and softening temperature increase as a result of the restricted molecular chain mobility imposed by rigid cellulose filaments. In addition, the DMA data revealed that amylose can occur as linkages in the crystallites. All these observations indicated that the interfacial adhesion between SCA and WF is relatively strong, even in absence of a coupling agent.     

Fabrication of hydroxyapatite and TiO2 nanorods on microarc-oxidized titanium surface using hydrothermal treatment

AC-type microarc oxidation (MAO) and hydrothermal treatment techniques were used to enhance the bioactivity of commercially pure titanium (CP-Ti). The porous TiO₂ layer fabricated by the MAO treatment had a dominant anatase structure and contained Ca and P ions. The MAO-treated specimens were treated hydrothermally to form HAp crystallites on the titanium oxide layer in an alkaline aqueous solution (OH-solution) or phosphorous-containing alkaline solution (POH-solution). A small number of micro-sized hydroxyapatite (HAp) crystallites and a thin layer composed of nano-sized HAps were formed on the Ti-MAO-OH group treated hydrothermally in an OH-solution, whereas a large number of micro-sized HAp crystallites and dense anatase TiO₂ nanorods were formed on the Ti-MAO-POH group treated hydrothermally in a POH-solution. The layer of bone-like apatite that formed on the surface of the POH-treated sample after soaking in a modified simulated body fluid was thicker than that on the OH-treated samples.     

Calculation of the Thermal Parameters of Boron Silicide by Differential Scanning Calorimetry

The DSC, TG, DTA, and DTG analyses of boron silicides, which are widely applied in radiation material science and nuclear technology, have been performed depending on the thermal treatment rate. The kinetic parameters (energy, enthalpy, oxidation reaction rate, heat capacity, and activation energy) of effects occurring in the thermal treatment of boron silicides of 99.5% purity within a temperature range of 25–900°C at a rate of 5–20°C/min have been established. It has been established that the phase transition typical for silicides with its central peak at a temperature 572 ± 5°C can exist in boron silicides depending on the thermal treatment rate. In TG and DTG spectra, this appears as an oxidation thermal effect at T ≥ 660°C with a change increase in mass of nearly 9%.     

水热法制备蒲公英状微晶和纳米带状β-SrV2O6及微结构表征

"利用Sr(NO3)2和V2O5作为反应前驱物, 已二酸作为矿化剂,在水热法反应条件下成功制备了微米尺寸蒲公英状及纳米尺寸的纳米带状β-SrV2O6晶微体. 通过粉末X衍射和电子显微镜的研究分析,结果表明所得的反应生成物属于正交晶系,其晶格常数为a=9.694 ?,b=3.687 ?,c=12.570 ? (空间群Pnma). 电子显微结果表明蒲公英状的微晶是揭示许多棒状微晶呈球型放射状构成的图案,而纳米带状的β-SrV2O6则呈现显示良好的挠性. 两者的微晶体生长方向沿h010i晶轴方向. 详细探讨了水     

Effect of hydrothermal treatment on the acidity distribution of γ-Al2O3 support

The influence of hydrothermal treatment on the total acidity and the acidity distribution of γ-Al₂O₃ were studied in this paper. The experimental results indicated that the hydrothermal treatment of γ-Al₂O₃ at moderate condition (140 °C, 1.0-24.0 h) led to the formation of the plate-like γ-AlOOH crystallites with different morphologies, which resulted in the change of the surface acidity of the corresponding γ-Al₂O₃ supports. The increase of the reaction time in the period of 1.0-2.0 h led to the increase of the specific surface area, the surface OH, the total acidity and the ratio of the weak acidity in the acidity distribution of γ-Al₂O₃. The further prolongation of reaction time caused the overgrowth of γ-AlOOH crystallites, leading to the decrease of the specific surface area, the surface OH and the total acidity of the corresponding γ-Al₂O₃.     

Ultra-stable temperature control in EPR experiments: thermodynamics of gel-to-liquid phase transition in spin-labeled phospholipid bilayers and bilayer perturbations by spin labels

An ultra-stable variable temperature accessory for EPR experiments with biological samples has been designed and tested. The accessory is comprised from a digitally controlled circulator bath that pumps fluid through high-efficiency aluminum radiators attached to an EPR resonator of a commercial X-band EPR spectrometer. Temperature stability of this new accessory after a 15 min re-equilibration is at least +/-0.007 K. For a standard 1-cm-long capillary sample arranged inside an EPR tube filled with silicon oil, the temperature variations do not exceed +/-0.033 K over the sample temperature range from 283 to 333 K. This new accessory has been tested by carrying out a comparative spin-labeling EPR and differential scanning calorimetry (DSC) study of the gel-to-liquid phase transition in multilamellar vesicles (MLV) composed of a synthetic phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC). We demonstrate that the gel-to-liquid phase transition temperatures of MLV DMPC measured by EPR and DSC agree within +/-0.02 K experimental error even though the sample for EPR study was labeled with 1 mol% of 5PC (1-palmitoyl-2-stearoyl-(5-doxyl)-sn-glycero-3 phosphocholine). Cooperative unit number measured by EPR, N=676+/-36, was almost 50% higher than that obtained from DSC (N=458+/-18). These high values of N indicate that (i) the lipid domains should include at least several spin-labeled lipid molecules and (ii) the spin-probe 5PC molecules are not excluded into domains that are different from the bulk lipid phase as was speculated earlier. Overall, our data provide DSC and EPR evidence that in studies of the gel-to-liquid phase transition, the effect of bilayer perturbation by spin-labeled lipids is negligible and therefore thermodynamic parameters of the phase transition can be accurately measured by spin-labeling EPR. This might serve as an indication when spin-labeled molecules with structures similar to those of lipids are introduced at low concentrations, they are easily accommodated by fluid phospholipid bilayers without significant losses of the lipid cooperativity.