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Aromatic polyimides have excellent thermal stability, mechanical strength and toughness, high electric insulating properties, low dielectric constants and dissipation factors, and high radiation and wear resistance, among other properties, and can be processed into a variety of materials, including films, fibers, carbon fiber composites, engineering plastics, foams, porous membranes, coatings, etc. Aromatic polyimide materials have found widespread use in a variety of high-tech domains, including electric insulating, microelectronics and optoelectronics, aerospace and aviation industries, and so on, due to their superior combination characteristics and variable processability. In recent years, there have been many publications on aromatic polyimide materials, including several books available to readers. In this review, the representative progress in aromatic polyimide films for electronic applications, especially in our laboratory, will be described.

The paper studies the influence of anisotropy of properties and structural inhomogeneity on hardness and mechanical properties of titanium Ti-4Al-3 V alloy produced by wire-feed electron-beam additive manufacturing. Tensile and compressive strength testing of the alloy specimens determines its elastic modulus and strength properties at different points. VIC-3D digital optical system is used to study the mechanical properties of the material under stress. The fractography analysis explains the observed behavior of the material under different loading. It is shown that after the tension, specimens possess close values of mechanical properties in various directions, except for their bottom, where the structure changes due to partial mixing of deposited and substrate materials. Just the material plasticity changes notably in the volume, which is the highest in the growth direction. This is probably stipulated by the low number of barriers to the dislocation motion during tension. In compressive strength testing, constrained conditions for the dislocation motion in columnar grains provide a higher strength for specimens cut in the growth direction, than for those cut in the printing direction. All this will allow us to more accurately choose the hardening technology of such materials and probably recommend methods of fabricating small-sized parts.

The traditional high-temperature preparation process of polyimide can cause many problems and limits the wider application in extreme conditions. An important challenge to be solved urgently is the reduction of imidization temperature. In this work, twelve kinds of polyimide films with different chain rigidity were prepared at low temperature of 200 °C, in the absence or presence of imidazole used as the catalyst. The molecular rigidity and free volume were theoretically calculated, and relationship between structure and properties were systematically studied. The results show that imidization reaction under low temperatures is significantly affected by the rigidity of molecular chains. The rigid structure of polyimide is not conducive to the low-temperature imidization, but this adverse effect can be eliminated by adding catalyst, resulting the notably increased imidization degree. The optical and thermal properties can be improved to a certain extent for the chemically catalyzed system, resulting in relatively higher heat resistance and thermal stability. While the mechanical performance could be determined by complicating factors, greatly different from polyimide films prepared by high temperature method. To investigate aggregation structures of films, the effect of chain rigidity and catalyst on the stacking or orientation of molecular chains was further elaborated. This work can contribute to the understanding of chemically catalyzed imidization that is rarely reported in the existing research, and will provide guidance for the low-temperature preparation of high-performance polyimides.

In this study, a simple one-step template-free solution method was developed for the preparation of poly(3,4-ethylenedioxythiophene) (PEDOTs) with different morphologies by adjusting various ratios of oxidant (FeCl3·6H2O) to monomer (3,4-ethylenedioxythiophene (EDOT)). The results from structural analysis showed that the structure of PEDOT was strongly affected by the oxidant/monomer ratio, and the polymerization degree, conjugation length, doping level, and crystallinity of PEDOT decreased with increasing of the oxidant/monomer ratio. The morphological analysis showed that PEDOT prepared from an oxidant/monomer ratio of 3:1 displayed a special coral-like morphology, and the branches of ‘coral’ would adjoin or grow together with increasing content of oxidant in the reaction medium; consequently, the morphology of PEDOT changed from coral to sheets (at an oxidant/monomer ratio of 9:1). The electrochemical analysis proved that the PEDOT prepared from an oxidant/monomer ratio of 3:1 had the lowest resistance and the highest specific capacitances (174 F/g) at a current density of 1 A/g with a capacity retention rate of 74% over 1,500 cycles, which indicated that the PEDOT with a coral-like morphology could be applied as a promising electrode material for supercapacitors.

For many years, TiO2-based materials and improving their properties in order to expand their application areas have been the focus of numerous research groups. Various innovative approaches have been proposed to improve the photocatalytic and gas-sensing properties of TiO2 nanostructures. In this review, we aim to synthesize the available information in the literature, paying special attention to the sol–gel technology, which is one of the most frequently used methods for TiO2 synthesis. The influence of dopants on the structural, morphological, optical, and electrical properties of TiO2 and the way to modify them in a controlled manner are briefly discussed. The role of shallow and/or deep energy levels within the TiO2 bandgap in the electron transport behavior of doped TiO2 is emphasized. Selected research on photocatalytic applications in water disinfection, wastewater treatment, and self-sterilizing coatings that contribute to improving the quality of human life and environmental preservation is highlighted. A survey of biosensors that are closely related to medical applications such as cancer detection, implantology, and osteogenesis is also provided. Finally, the pressing problems that need to be solved in view of the future development of TiO2-based nanostructures are listed.

Mesophase pitch is usually prepared by radical polymerization or catalytic polymerization from coal tar, petroleum, and aromatic compounds, and the catalytic synthesis of mesophase pitch from pure aromatic compounds is more controllable in the preparation of high-quality mesophase pitch. However, the corrosive and highly toxic nature of the catalyst has limited the further development of this method. In this study, mesophase pitch was synthetized using ethylene tar and naphthalene as raw materials and boron trifluoride diethyl etherate as a catalyst. The effect of the catalytic reaction on the structure and properties of the mesophase pitch was investigated. The results show that naphthalene plays an important role in the mesophase content and reaction pressure (from above 6 MPa to 2.35 MPa). Mesophase pitch with fine-flow texture can be prepared by introducing more methylene groups, naphthenic structures, and aliphatic hydrocarbons during synthesis. Carbon fibers prepared from mesophase pitch show a split structure, and the thermal conductivity is 730 W/(m·K). This work provides theoretical support for lower toxicity and causticity and for reaction-controlled technology for the synthesis of high-purity mesophase pitch.

AbstractTo investigate the effects of the different types and content of monomer units and molecular weights Mns on the thermal, mechanical and barrier properties of the copolymers. Here, three unsaturated poly(L-lactic acid-co-butyrate itaconate) (P(LA-BI)), poly(L-lactic acid-co-butyrate fumaric) (P(LA-BF)), and poly(L-lactic acid-co-butyrate maleic) (P(LA-BM)) copolymers were synthesized by melt polycondensation and subjected to repeated grading. Based on a solvent/non-solvent (chloroform/n-heptane) mixture, an original sample was fractionated into 9–10 fractions. As the fractionation proceeded, the alterations in the monomer units content and Mns of the three copolymers showed disperate trends. The P(LA-BI) with 10.4% PBI content reaches a maximum value of Mn 8.82 × 104 and has the best physical properties. The elongation at break and oxygen transmission rate (OTR) were 491.3% and 106 cm3/m2 d–1 respectively, and the degree of crosslinking was 7.7%. P(LA-BF) exhibited the second-best Mn and physical properties, while P(LA-BM) displayed the worst physical properties. The elongation at break was 3.4% and the oxygen transmission rate (OTR) was 389 cm3/(m2 d) at 7.3% BM.

The development of membrane materials with high transport and separation properties for the removal of higher hydrocarbons from gas mixtures is an important and complex task. This work examines the effect of a cross-linking agent on the structure and transport properties of polydecylmethylsiloxane (C10), a material characterized by high selectivity towards C3+ hydrocarbons. C10 was cross-linked with various diene hydrocarbons, such as 1,7-octadiene (C10-OD), 1,9-decadiene (C10-DD), 1,11-dodecadiene (C10-DdD), and vinyl-terminated polysiloxanes, of different molecular weights: 500 g/mol (C10-Sil500) and 25,000 g/mol (C10-Sil25-OD). Using a number of characterization methods (IR-spectroscopy, WAXS, DSC, toluene sorption, and gas permeability), it was revealed that a change in the type and length of the cross-linking agent (at the same mole concentration of cross-linking agent) led to a significant change in the structure of the polymer material. The nature of cross-linking agent affected the arrangement of the decyl side-groups of the polymer, resulting in noticeable differences in the solubility, diffusivity, permeability, and selectivity of tested gases (N2, CH4, C2H6, and C4H10). For instance, an increase in the length of the hydrocarbon cross-linker was associated with a drop of n-butane permeability from 5510 (C10-OD) to 3000 Barrer (C10-DdD); however, the transition to a polysiloxane cross-linker led to an increase in corresponded permeability up to 8200 Barrer (C10-Sil25-OD). The n-butane/nitrogen selectivity was significantly higher for diene-type cross-linkers, and the maximum value was achieved for 1,7-octadiene (α(C4H10/N2) = 104).

The current work presents the fabrication of polyaniline (PAni)/polyvinyl alcohol (PVA) nanofiber composites through electrospinning. The morphological properties of the sample evaluated by employing the field emission scanning electron microscope (FESEM) and the diameters of the samples are between 141 to 234 nm. The presence of both PVA and PAni in the nanofiber structure was evaluated with the aid of Fourier-Transformation Infrared Spectroscopy (FTIR). When a rifampicin-doped PVA film and a rifampicin-doped nanofiber PAni/PVA film were irradiated with a continuous wave laser beam at a wavelength of 532 nm, diffraction ring patterns (DFRPs) were seen. The nonlinear refractive index (NLDX) , was determined from the number of observed rings. Large value obtained of the order of 212.48 × l0 –8 cm 2 /W for PAni/PVA nanofiber composites. The change in the nonlinear refractive index , depends primarily on both the natural refractive index of the material and the NLDX, in which diffraction patterns play a major role in this change. In addition to that, the optical limiting) (qualities were investigated. Within a solid PAni/PVA host, the dye shows of some impressive optical limiting features. It has been discovered that the mechanism responsible for the limitation of optical sensitivity is mostly of a thermal nature.

The films with various orientation degrees were produced by polyvinylidene fluoride (PVDF) melt extrusion. The crystalline structure of the oriented films was studied using wide-angle X-ray scattering. The relaxation processes within the temperature range of 273–333 K were investigated using thermally stimulated depolarization (TSD) method. Within examined temperature range, two relaxation processes were observed, which are assumed to be associated with dipolar-segmental motion. The intensity of these relaxation processes declined as the degree of orientation increased. In order to study the influence of crystallinity degree on the observed relaxation processes, the extruded PVDF films were subjected to isometric annealing. It was observed that an increase in the crystallinity degree leads to the growth of thermally stimulated depolarization intensity in the temperature range of 300–310 K and its decrease in the temperature range of 280–290 K.