Polymer Science, Series A最新文献

Ceramic/polymer composites exhibit high dielectric constant, low dielectric loss, and high energy storage density. In this work, the characteristics of the spin-coating process to obtain a thin and uniform composite film without obvious defects were used to prepare composite films BaTiO₃/PVDF. High-quality composite films enable better study of their macro- and microstructures, dielectric and energy storage properties. The results show that the BaTiO₃/PVDF composite films prepared by the spin-coating process exhibit good uniformity in both macroscopic and microstructure. The average thickness is about 7 μm. At the same frequency, the dielectric constant increases with the increase in BaTiO₃ content. The dielectric constant of 30 vol % PVDF composite film reached 62 at 100 Hz, which was nearly 6.8 times higher than that of pure PVDF. In addition, the dielectric loss of the composite film first decreased and then increased with the increase of frequency. With increasing of the BaTiO₃ content, the breakdown strength of the composite film decreased. The P_max and U_charge of the composite film increased with increasing of the electric field. The P_max of 30 vol % composite film was 4.41 μC/cm² at 900 kV/cm_. The energy storage density of 15 vol % composite film was 6.916 J/cm³ at 1500 kV/cm.

The rheokinetics of gelation of poly(vinyl alcohol) aqueous solution systems with chemical crosslinks and physical junctions, including hybrid ones, has been studied. Hydrogels are obtained using glutaraldehyde and/or tetramethoxysilane as crosslinking components. It has been shown that at the initial step of gelation (until the systems reach critical gelation conversion) the efficiency of the process is determined by the concentration of the crosslinking agent rather than the chemical nature of network crosslinks. A comparative analysis of the mechanical properties of chemical, physical, and hybrid hydrogels at various temperatures is performed. Quasi-static uniaxial compression and tension tests make it possible to establish the contribution of network junctions and crosslinks to the behavior of hybrid hydrogels and their distinctive features.

A series of molecularly imprinted and nonimprinted cryogels based on the copolymer of 2‑hydroxyethyl methacrylate and N,N '-methylene-bis(acrylamide) are synthesized at various ratios and contents of comonomers in the polymerization mixture. The resulting materials are characterized in terms of surface morphology, swelling ability, average pore size, porosity, and compression mechanical characteristics. In addition, a comparative assessment of the adsorption properties of the molecularly imprinted and nonimprinted cryogels with respect to a target protein (α-chymotrypsin) in the dynamic mode is performed, as well as the in vitro biocompatibility of the cryogels using two cell lines.

Resin mineral composites (RMC) have attracted a great deal of attention in ultra-precision machining because of their excellent vibration-dampening properties; however, their poor mechanical properties limit their wide applications. Adding reinforcing fibers is an effective way to improve the mechanical properties of RMC. This paper systematically studies the effect of aramid fibers as reinforcing components on the mechanical and thermal expansion properties of RMC. Results show that the mechanical strength of RMC can be effectively improved by a suitable selection of surface treatment methods and parameters. The mechanical strength of RMC reached its maximum value when the ultrasonic power was 200 W and the treatment time was 6 min; the mechanical strength of RMC reached its maximum value when the concentration of phosphoric acid oxidation was 20 wt % and the treatment time was 2 h. This study investigates the effect of different surface treatments on aramid fibers on the mechanical properties of resin mineral composites, optimizes the aramid fiber surface treatment parameters, enhances the mechanical properties of resin mineral composites, and extends the applications of resin mineral composites in high-speed processing and ultra-precision processing.

Abstract

The crystal morphologies of poly(ε-caprolactone) solvent-cast films in the absence and presence of multi-walled carbon nanotubes were observed using polarized optical microscopy. The experimental results indicated ring-banded spherulites containing polygonal holes could be induced by dewetting on the surface of the substrate. The polymer crystals assembled into a hierarchical structure induced by the change of the crystallization temperature. Further it was found that the loading of nanotubes into polymer matrix could change the ring-banded structure in the spherulites.

Amphiphilic copolymers of amino acids capable of self-assembly in aqueous media into nanoparticles are of interest as potential drug delivery systems. In this work, a series of amphiphilic copolymers of lysine and phenylalanine with different chirality and content of monomer units are synthesized and characterized. Effect of the composition of copolymers on the characteristics and physicochemical and biological properties of nanoparticles formed due to self-assembly is studied. Specifically, the hydrodynamic characteristics of nanoparticles are determined and compared with average diameters in the dry state. Critical aggregation concentrations are assessed and effect of the рН of medium and the time of incubation on the stability of dispersions of nanoparticles is investigated. In addition, the data on the cytotoxicity of nanosystems depending on the chirality of hydrophobic amino acid are obtained.

To maintain CO₂/O₂ permselectivity of poly(lactic acid) (PLLA) microporous films for better preservation of fresh produce, Polytrifluoropropylmethylsiloxane (PTFPMS) was introduced into PLLA to prepare PLLA-PTFPMS-PLLA (PLTL) block copolymer. And PLTL-n% microporous films were prepared using varying ratios of chloroform/acetone blended solvents as the film-casting solution in this study. PTFPMS filled a portion of the micropores of the PLTL-n% film. While the micropores enhanced the O₂ and CO₂ dioxide permeability of the PLLA microporous film, PTFPMS maintained the CO₂/O₂ selective permeability of the film. In comparison to PLLA films, the CO₂ permeability of mixed solvents-treated PLTL-20% film increased from 1.99 × 10^–8 to 10.08 × 10^–8 cm³ m/m² h Pa, O₂ permeability increased from 0.70 × 10^–8 to 2.02 × 10^–8 cm³ m/m² h Pa, and CO₂/O₂ permselectivity increased from 2.9 to 5.0 at 5°C. In addition, PLTL-n% microporous films also have good flexibility and UV shielding properties.

The films of heterocyclic copolyaramide used at NPO OOO “LIRSOT” for the production of high-strength polyaramide threads are obtained, their gas transport characteristics for helium, oxygen, and carbon dioxide are studied, and the parameters of free volume elements are investigated by positron annihilation lifetime spectroscopy. According to the data obtained, the copolyaramide under study belongs to the class of polymers with high barrier characteristics and its properties are close to those of the commercial samples of thermotropic liquid-crystalline copolyesters Vectra. The low values of gas permeability of copolyaramide are related to decreased gas diffusion coefficients. A comparison of the activation energies of permeability, diffusion, and sorption enthalpy of gases shows that these parameters are also comparable to those of barrier polymers. The gas permeability data are confirmed by positron annihilation lifetime spectroscopy: the sizes of free volume elements obtained for copolyaramide (R₃ = 2.5 Å) are also comparable with those for copolyester Vectra (R₃ = 2.1 Å). The results of this study demonstrate that the tested domestic heterocyclic copolyaramide can be used for the manufacture of barrier films and coatings as a substitute for Vectra liquid-crystalline copolyesters.

Conductive hydrogel-based flexible strain sensors have gradually attracted the attention of scientific researchers in recent years. They are capable of converting invisible mechanical stimulus signals into visible electrical signals and have excellent biocompatibility and good electrical conductivity, which also provide the basis for the development of flexible electronic devices. Nowadays, conductive hydrogel, as the core component of flexible sensors, puts forward higher requirements for sensitivity, fast response, and cycle stability to adapt to human activity detection and health monitoring. In this paper, acrylamide (AM), cellulose nanocrystals (CNC), and sodium alginate (SA) were used as raw materials to prepare PAM/CNC/SA double network hydrogel by in situ free radical polymerization. Soaked in the CaCl₂ solution, a PAM/CNC/SA-Ca²⁺ double-network conductive hydrogel is formed. The results show that the addition of CNC can significantly improve the mechanical properties of the hydrogel. In addition, the introduction of the Ca²⁺ ion has a certain positive effect on the conductivity of the hydrogel. At the same time, the conductive hydrogel has good strain sensitivity (gauge factor up to 16.63). Therefore, conductive hydrogels have potential application value and broad application prospects in the field of flexible sensors.

Filled composites of low-density polyethylene with nanocarbon fillers, namely, graphite nanoplates and reduced graphene oxide, of various compositions, are obtained in a solid phase under shear deformations in a rotary disperser. A difference in the structure of the obtained nanocomposites is demonstrated using scanning electron microscopy. A comparative study of the mechanical properties, porosity, and rheological behavior of the composites is carried out. It is revealed that the nature of graphene nanofillers and the composition of blends influence the characteristics of the resulting materials.