Thermal stabilization of polypyromellitimide films

The paper is devoted to the modification of the polyimide based on pyromellitic dianhydride and 4,4'-diaminodiphenyloxide with phosphoric and boric anhydrides. It is demonstrated that, due to the use of phosphorus- and boron-containing polyamidoacid compositions for casting the polyimide films, one can significantly increase their heat resistance without substantial expenditures while, at the same time, preserving the film-forming ability and mechanical properties of the polyimide.     

New polypyromellitimide films based on cyclotriphosphazene and bisaspartimide derived diamines

Three new thermally stable polypyromellitimide films were made by the thermal cyclodehydration of the corresponding polyamic acids obtained by the polymerization of pyromellitic dianhydride with 4,4′-bis{N²-[4-(4-aminobenzyl)phenyl]aspartimido} diphenylmethane, 4,4′-bis{N²-[4-(4-aminophenoxy)phenyl]aspartimido} diphenylether, and bis(4-aminophenoxy)tetrakis (4-phthalamic acid phenoxy)cyclotriphosphazene. The bis(4-aminophenoxy)tetrakis (4-phthalamic acid phenoxy)cyclotriphosphazene was obtained from hexakis(4-aminophenoxy)cyclotriphosphazene involving its reaction with phthalic anhydride. The structure of these materials and precursors were characterized by using Fourier-transform-infrared (FT–IR) and proton nuclear magnetic resonance spectroscopy. The thermal stabilities of the films were evaluated by the thermogravimetric analysis, showing char yields at 800°C ranging from 68% to 58% in a nitrogen atmosphere and 24% in air atmosphere.     

Effect of orientation extension on the structure and physicomechanical properties of porous polyethylene films

Effects of the degree, velocity, and temperature of repeated extension of porous PE films on their structure and transport and mechanical properties are investigated. The sizes of through-flow channels and the permeability of porous films are determined via filtration porosimetry. A rise in the temperature and the degree of extension in the course of orientation extension noticeably increases the sizes of pores, the overall porosity, the specific surface area, and the permeability of the films and improves their mechanical characteristics.     

Effect of Al-doping on the structure and optical properties of electrospun zinc oxide nanofiber films

Electrospun ZnO precursor nanofibers of average diameters 122±64 nm, 117±44 nm and 110±39 nm were fabricated by controlling the Al concentration of a polymeric solution. The resulting nanofibers were characterized by the XRD, SEM, EDS, TEM, XPS and PL. The electrospun Al-doped ZnO nanofiber films were polycrystalline and composed of densely packed grains, with crystallite size ranging from 28.7 nm, 25.7 nm, 25.4 nm to 20.4 nm corresponding to the atomic concentration of aluminum from 0, 1.6, 2.5 to 5.8 at.%. The incorporation of aluminum resulted in a decrease trend in the grain size and lattice parameter of the ZnO nanofiber films. The room temperature PL spectra of all samples show three different emissions, including UV (ultraviolet) emission with an obvious blue shift, Vis (visible) emission and NIR (near infrared) emission, the intensity of which decreases monotonically as the doping concentration is increased except for the highest doping level. The impurity content correlates with changes in the PL spectra, and the appropriate Al doping can improve the optical properties of ZnO nanofibers. The small size effect and Al-doping or the impurity incorporation should be responsible for the blue shift observation in Al-doped ZnO nanofiber films.     

Effect of synthesis conditions on the structure and sorption properties of films based on mesoporous tin dioxide

We have conducted a comparative study of the synthesis conditions for mesoporous materials and films based on tin dioxide in the presence of different types of templates, and we have studied their thermal stability and sorption properties. We demonstrate the advantage of using alcoholic reaction media and nonionic templates (triblock copolymers Pluronic-123 and Pluronic-127) to obtain thin films of mesoporous SnO₂ with relatively high parameters for the porous structure (V_meso = 0.15 cm³/g, S_BET = 147 m²/g) and cassiterite crystallite sizes down to 2.7 nm, significantly smaller than the thickness of the walls.     

Optical properties and structure of drawn polyethyleneterephtalate-polyethylene films

Films made by coextrusion of polyethyleneterephtalate and low density polyethylene exhibit specular reflection of light when stretched. Unlike the behaviour of films made of pure PET, where specular reflection is rare and does occur at extremely high stretching rates only, PET/LDPE films show specular reflection independent of the stretching rate.A film, containing 70% PET and 30% LDPE, prepared by coextrusion of the two components, has been investigated by scanning electron microscopy, light microscopy and by measuring the optical properties with a spectrophotometer. The (unstretched) as prepared sample has been compared with a sample stretched to =4.The optical measurements show as a result of the stretching a strong decrease of the transmittance and an increase of the remittance. While there is no drastic change of the dispersion (which is only slight), the increase of the refractive index indicates some straininduced crystallization.The scanning electron micrographs show long, needlelike voids and indicate a fractionation of the two components as a result of the stretching. This fractionation has been investigated by heating the samples up under the light microscope: while the stretched sample shows a separation of the components, the unstretched sample does not.Dedicated to Prof. Dr. F. H. Müller.     

海藻酸钠-硫酸软骨素共混膜的结构及性能研究

利用溶液共混法成功制备了新型生物膜材料-硫酸软骨素共混膜,通过红外光谱、X-射线衍射、原子吸收光谱和扫描电镜对共混膜的结构进行了表征,并测定了不同配比共混膜的抗张强度、断裂伸长率,吸水率,同时考察了介质pH值和离子强度对共混膜吸水率的影响。结果表明:共混膜中海藻酸钠、软骨素之间具有较强的相互作用和良好的相容性,共混膜具有良好的力学性能。作为一种潜在的生物材料可望在生物医学领域得到应用。     

Interaction of polypyromellitimide with nitrogen dioxide

The mechanism of interaction of nitrogen dioxide with aromatic polyimides is considered by the example of polypyromellitimide. The formation of stable radicals of acylarylaminoxyl, iminoxyl and phenoxyl types has been detected by electron paramagnetic resonance spectroscopy. Acylarylaminoxyl radicals were detected in polypyromellitimide after its exposure to nitrogen dioxide at room temperature followed by pumping nitrogen dioxide from the samples. Iminoxyl and phenoxyl radicals were formed during thermolysis of the nitration products of the polymer at 373 K. The proposed mechanism is based on the reaction of dimers of nitrogen dioxide in the form of nitrosyl nitrate. It was observed that intermediate radical cations and nitric oxide were formed in the primary reaction of electron transfer from the polyimide to nitrosyl nitrate. The subsequent cage reactions with participation of radical cations and nitric oxide give nitroso compounds and nitrates which are precursors of stable nitrogen-containing and phenoxyl radicals.     

Investigation of structure and properties of divinylbenzene-styrene copolymer films

A method for preparation of divinylbenzene-styrene copolymer porous layer on the inner wall of a fused silica capillary was developed. Capillary gas chromatography was used to investigate the sorption capacity of copolymer film toward substances of various classes.     

Effect of bovine serum albumin on the structure and properties of Langmuir Blodgett films based phosphocholine and cholesterol

Mono- and bilayer Langmuir-Blodgett films based on phosphocholine and cholesterol and prepared by horizontal and vertical deposition are investigated by atomic force microscopy. It was found that bovine serum albumin (BSA) included at the stage of film formation. At the same time, isolation has a considerable effect on their structure. It was shown that the globular formation of nanostructures with heights of 4–7 nm occurs as a result of transferring lipids to a hydrophobic surface from a subphase containing BSA, indicating the reorganization of monolayers during protein isolation and inclusion in its composition.     

Effect of multiscale structure on the gas barrier properties of poly(lactic acid)/Ag nanocomposite films

Poly(lactic acid) (PLA) is the most suitable for biodegradable packaging film because of its excellent integrated property, but the poor gas barrier property is its weakness. In this study, a nanocomposite film based on PLA incorporated with 0‐, 1‐, 3‐, 5‐, 10‐, or 15‐wt% nano‐Ag was developed. Effect of multiscale structure on the barrier properties of PLA/nano‐Ag films was studied. The PLA nanocomposite film with 5‐wt% nano‐Ag had the lowest water vapor permeability (WVP) value. Oxygen transmission rate (OTR) value for PLA nanocomposites with 3‐wt% nano‐Ag was found to be the lowest among all the samples. Multiscale structure was demonstrated by the scanning electron microscopy, Fourier transform‐infrared spectroscopy, X‐ray diffraction measurement, and differential scanning calorimetry results. The crystallinity of the PLA phase increased with the content of nano‐Ag in the PLA composites. The evolution of the PLA phase crystallinity could improve the barrier properties of PLA/nano‐Ag composite films for food packaging applications. From the view of multiscale structure, it is better to achieve a balance among short‐range conformation in the amorphous region, long‐range‐ordered structure, and ordered aggregated structure to improve the barrier properties of PLA/nano‐Ag composite films.     

Effect of water on the mechanical properties of collagen films

The effect on water on mechanical properties of collagen films has been studied. The S-shaped sorption isotherm is separated into an adsorption curve C₁ and a solution curve C₂. From the C₂ curve, a value of 0.8 is calculated for the Flory-Huggins interaction parameter χ₁. The dynamic shear modulus G′, loss modulus G″, and loss tangent tan δ determined as functions of water content indicate two dispersions at low and at high water content. The region of water content from about 0.05 to 0.1 g/g, G′ decreases suddenly, G″ has a peak, and tan δ increases, corresponds to the region where the C₂ component of sorption becomes detectable. Another dispersion occurs at water contents above 0.2 g/g. A composite curve can be obtained by shifting stress-relaxation curves obtained at different humidities along the log time axis. When only the C₂ component of sorbed water is taken into account, the shift factor a_c is explained by a relation of Fujita and Kishimotos' based on free-volume theory. Shift factor for the relaxation curves of wool fibers, except for an initial part at times of less than 1 sec, are described by the same equation. The parameter β in the equation has the same value of 0.16 for both collagen and wool.     

Surface structure and photoluminescence properties of AZO thin films on polymer substrates

Al‐doped zinc oxide (AZO) thin films were deposited on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates by radio frequency (RF) magnetron sputtering method at room temperature. The effects of film thickness on the surface structure and the photoluminescence properties of the films were investigated by atomic force microscopy (AFM), secondary ion mass spectroscopy (SIMS) and room temperature photoluminescence (PL). AFM analysis showed that the surface of all films was extremely flat and uniform at nanoscale. Root mean square (RMS) value of the surface roughness which scanned the surface area of 3 µm by 3 µm and grain size increased with increasing the film thickness. Thus, the surface morphology of the films became rough because of the coarse grains. The depth profile of AZO layers was analyzed by SIMS. It was found that the thickness of the AZO layer is almost same with the desired film thickness. The PL intensity of the dominant peak decreased and shifted slightly towards the shorter wavelengths with increasing the film thickness. According to the relationships between luminescence intensity and crystalline characteristics, it was observed that the intensity of the peak decreased by the increased surface area of the grains. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of structure on properties of aromatic-aliphatic polybenzimidazoles

Homopolymers and copolymers containing the polybenzimidazoles ring were prepared from terephthalic acid (T), fumaric acid (F), and 3,3′-diaminobenzidine tetrachloride (DAB) in polyphosphoric acid. The polymers were characterized by viscometry, infrared spectroscopy, and nitrogen analyses. The effect of copolymer composition on the ultraviolet and visible spectra, solubility in various solvents, and density was also investigated. The relative thermal stability of the various polybenzimidazoles was investigated by using dynamic thermogravimetry in air. Polybenzimidazole derived from terephthalic acid was most stable, and the introduction of aliphatic residues resulted in a decrease in thermal stability. However, the homopolymer of fumaric acid was more stable than the copolymers of fumaric acid and terephthalic acid.     

Effect of thickener structure on paper-coating color properties

Physical and chemical properties of clay-based paper-coating colors have been characterized. The “surface potential” (zeta potential) of kaolin particles used in paper-coating formulations was determined as functions of pH and sodium polyacrylate (used as a dispersant) concentration. The optimal pH and dispersant concentration have been established. The effect of adsorption of two different thickeners on the kaolinite particle potential was also investigated. The rheological properties of coating colors, thickened with an associative polymer and a commonly used thickener, have been compared. The rheological behavior of all the coating colors studied was found to be similar, except for the magnitude of the elastic modulus, which was considerably larger for the more hydrophobic thickener. The water-retention properties of the colors could be qualitatively correlated with the molecular structure of the thickeners. An interaction mechanism (e.g. formation of hydrophobic micellar domains) between kaolinite particles and the associative polymer has been proposed. Received: 10 August 2000/Accepted: 2 January 2001     

Effect of single-walled carbon nanotubes and carbon nanofibers on the structure and mechanical properties of thermoplastic polyimide matrix films

The effects of additives of single-walled carbon nanotubes prepared via electric-arc synthesis and carbon nanofibers produced via gas-phase synthesis on the crystallization capacities and mechanical and electric properties of composite films of a thermoplastic polyimide (PI) matrix based on 1,3-bis-(3,3′, 4,4′-dicarboxyphenoxy)benzene and 4,4′-bis-(4-aminophenoxy)biphenyl after their uniaxial drawing and additional annealing are studied. The use of these fillers induces the heterogeneous nucleation of a crystalline phase of PI on the nanoparticle surface. A higher specific interface area in the case of addition of carbon nanotubes relative to that of carbon nanofibers leads to the formation of the crystalline structure of PI with a small crystallite size and high imperfection. Uniaxial drawing leads to the formation of a supermolecular structure that is optimum for crystallization during additional annealing and removes the kinetic hindrances to crystal growth. The properties of these fillers have a significant effect on the orientation of the nanoparticles and the matrix macromolecules during the uniaxial drawing of the films, which is accompanied by an increase in the elastic modulus with an increase in the draw ratio and the ability of the composite films to undergo orientational crystallization during additional annealing.     

Effect of sol temperature on the structure,morphology, optical and photoluminescence properties of nanocrystalline zirconia thin films

Transparent nanocrystalline zirconia thin films were prepared by sol–gel dip coating technique using Zirconium oxychloride octahydrate as source material on quartz substrates, keeping the sol at room temperature (SET I) and 60 °C (SET II). X-ray diffraction (XRD) pattern shows the formation of mixed phase [tetragonal (T) + monoclinic (M)] in SET I and a pure tetragonal phase in SET II ZrO₂ thin films annealed at 400 °C. Phase transformation from tetragonal to monoclinic was achieved in SET II film annealed at 500 °C. Atomic force microscopy analysis reveals lower rms roughness and skewness in SET II film annealed at 500 °C indicating better optical quality. The transmittance spectra gives a higher average transmittance >85% (UV–VIS region) in SET II films. Optical spectra indicate that the ZrO₂ films contain direct—band transitions. The sub- band in the monoclinic ZrO₂ films introduced interstitial O⁻defect states above the top of the valance band. The energy bandgap increased (5.57–5.74 eV) in SET I films and decreased (5.74–5.62 eV) in SET II films, with annealing temperature. This is associated with the variations in grain sizes. Photoluminescence (PL) spectra give intense band at 384 and 396 nm in SET I and SET II films, respectively. A twofold increase in the PL intensity is observed in SET II film. The “Red” shift of SET I films and “Blue” shift of SET II films with annealing temperature, originates from the change of stress of the film due to lattice distortions.     

Dose effects in radiation-induced conductivity of polypyromellitimide

Dose effects in radiation-induced conductivity of polypyromellitimide were numerically simulated in terms of the Rose-Fowler-Vaisberg model with allowance for bipolar carrier transport and the generation of radiation traps during irradiation. The reasons for the lack of a noticeable dose effect in this polymer upon pulse irradiation in light of its presence in the case of continuous irradiation are discussed.     

Effects of film structure on electrochromic properties of the multilayer films containing polyoxometalates

Multilayer films of tungstophosphate anion (P₂W₁₈) and poly(allylamine hydrochloride) (PAH) were fabricated on quartz and ITO substrates by layer-by-layer self-assembly method. These films were characterized by UV–vis spectroscopy, cyclic voltammetry (CV), chronoamperometric (CA), chronocoulometry (CC) and atomic force microscopy (AFM). The effects of film structure on multilayer electrochromic properties were investigated. The electrochromic responses of the composite films were related to the surface coverage of anion and multilayer thickness. It was found that higher concentration of polycation and anion, or adding salt to the polycation solution used for multilayer film preparation led to thicker and denser film structure which improved optical contrast and coloration efficiency whereas prolonged response time.