Polyacrylamide-based hydrogel filled with carbon quantum dots (PAA@CQDs) exhibiting intensive photoluminescence (PL) under UV irradiation was prepared. The exceptional capability of the Fe3+ ions to quench PAA@CQDs PL in aqueous solution was found. The PL recovery after repeated quenching was detected when hydrochloric acid was used as a regenerant, thus ensuring the PAA@CQDs reusability as a chemosensor for the Fe3+ ions detection in aqueous media.

Ultra-high molecular weight polyethylene (UHMWPE) is a promising material for preparation of membranes and Li-ion battery separators. Existing methods of their preparation are either hardly scalable or demand rather complex equipment. In this work UHMWPE separators were prepared via thermally induced phase separation method (TIPS) without additional drawing from the blends of the polymer with decalin and its mixtures with dioctyl adipate (DOA). It was shown that the final membrane morphology is a result of significant shrinkage of the initially formed structure upon drying form the extractant. In this case, shrinkage was favorable since it enables formation of the samples with intermediate porosity (63-86 %) from a very dilute solution of UHMWPE (1.5 % wt.). The shrinkage behavior was examined using optical microscopy. Mechanical and transport properties were evaluated using standard methods whereas electrochemical performance of the prepared samples was investigated by assembling the disc-like batteries and their exploitation at different C-rates. It was shown that the TIPS method can be successfully used to prepare porous flat films with a thickness as low as 30 mu m are applicable as Li-ion battery separators. The structure of the prepared membranes consists of three-dimensional, irregularly shaped leaf-like particles that are mechanically interlocked (entangled) rather than chemically bonded. An increase in the DOA content in the mixed solvent (from 0 to 30 % wt.) was detected to increase the crystallinity (from 74 to 91 %), melting point (from 132.8 to 134.2 degrees C), tensile strength (from 0.8 to 4.0 MPa), elongation at break (from 420 to 660 %) and puncture strength (from 0.27 to 1.83 gf mu m- 1) and decrease the thickness (from 72 to 30 mu m), mean through pore size (from 0.6 to 0.33 mu m) and permeance (from 2050 to 280 L m-2h- 1 bar- 1).

Oriented polyvinylidene fluoride (PVDF) films were obtained in multistage process based on melt extrusion of polymer. We investigated the results of the polymorphic α→β crystalline phase transformation in the PVDF films subjected to uniaxial stretching. During uniaxial extension both appearance of a polar piezo active crystalline structure and significant changes in the samples morphology were observed. Variations in the PVDF films morphology, polymorphic composition, and supramolecular structure upon transformation were detected with Fourier transform infrared spectroscopy, wide-angle X-ray scattering, and scanning electron microscopy techniques. Broadband dielectric spectroscopy was used to ascertain a change in molecular mobility of the polymer chains during α→β phase transformation. The relaxation processes, γ-, αа-, αс-, and interfacial polarization, in both α- and β-phases of PVDF were identified in the dielectric loss spectra and described with either Arrhenius or Vogel-Fulcher-Tammann equations. The analysis of the equations parameters allowed concluding that initiation of a polymorphic α→β transition through uniaxial extension results in hindering the relaxators mobility in the β-phase of PVDF samples, except γ-relaxators. This finding confirms a proposal that γ-relaxators are located in the amorphous part of PVDF. Uniaxial extension resulted in a substantial increase in the interfacial polarization, which can be attributed to the emergence of new interface boundaries.

We synthesised a polyacrylamide (PAA) hydrogel filled with fluorescent carbon quantum dots (CQDs) for environmental sensing application. The obtained PAA@CQDs composite was characterised using scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, photoluminescence (PL) spectroscopy, time correlated single photon counting and UV-visible spectroscopy. In the PAA@CQDs composite, CQDs were shown to retain their high PL properties. Being immersed into FeCl3 solutions, PAA@CQDs samples demonstrated intensive PL quenching because of Fe3+ ions absorption. The limit of the Fe3+ ions detection was determined to be 0.124 mu M. We showed the formation of non-PL complex between CQDs and Fe3+ ions, ensuring static mechanism of the PAA@CQDs PL quenching.

Hydrophobic N-doped carbon quantum dots (N-CQDs) were prepared using citric acid and L-phenylalanine through hydrothermal synthesis at optimum conditions (temperature T = 200 degrees C and time t = 9 h) and thoroughly investigated with different techniques. In organic solvents (ethanol, chloroform, dimethyl formamide, and xylene) under 350 nm excitation wavelength, N-CQDs exhibit intensive blue photoluminescence (PL) with the quantum yield equal to 36.5 %. Being embedded into polymer matrices (poly(methyl methacrylate) and epoxy resin), N-CQDs preserved their high PL.

A new method of fabricating porous membranes based on ultra-high molecular weight polyethylene (UHMWPE) by controlled swelling of the dense film was proposed and successfully utilized. The principle of this method is based on the swelling of non-porous UHMWPE film in organic solvent at elevated temperatures, followed by its cooling and further extraction of organic solvent, resulting in the formation of the porous membrane. In this work, we used commercial UHMWPE film (thickness 155 μm) and o-xylene as a solvent. Either homogeneous mixtures of the polymer melt and solvent or thermoreversible gels with crystallites acting as crosslinks of the inter-macromolecular network (swollen semicrystalline polymer) can be obtained at different soaking times. It was shown that the porous structure and filtration performance of the membranes depended on the swelling degree of the polymer, which can be controlled by the time of polymer soaking in organic solvent at elevated temperature (106 °C was found to be the optimal temperature for UHMWPE). In the case of homogeneous mixtures, the resulting membranes possessed both large and small pores. They were characterized by quite high porosity (45–65% vol.), liquid permeance of 46–134 L m−2 h−1 bar−1, a mean flow pore size of 30–75 nm, and a very high crystallinity degree of 86–89% at a decent tensile strength of 3–9 MPa. For these membranes, rejection of blue dextran dye with a molecular weight of 70 kg/mol was 22–76%. In the case of thermoreversible gels, the resulting membranes had only small pores located in the interlamellar spaces. They were characterized by a lower crystallinity degree of 70–74%, a moderate porosity of 12–28%, liquid permeability of up to 12–26 L m−2 h−1 bar−1, a mean flow pore size of up to 12–17 nm, and a higher tensile strength of 11–20 MPa. These membranes demonstrated blue dextran retention of nearly 100%.

Ternary mixtures of a semicrystalline (SC) polymer with a solvent and a nonsolvent are widely used primarily for preparation of membranes by nonsolvent induced phase separation (NIPS). A detailed analysis of the published studies devoted to phase equilibrium in such systems showed that the phase diagrams were either incomplete or presented in a schematic form. In the present paper, we propose a new method of plotting the ternary phase diagrams for the SC polymer – solvent – nonsolvent mixtures. This method is based on finding the location of the isotherm intersection with the curves on the temperature–composition pseudobinary phase diagrams for the SC polymer mixtures with solvent and binary mixtures of solvent and nonsolvent of different composition. The coordinates of the intersection points were used to plot for the first time the complete ternary phase diagram for the widely used mixture of polyvinylidene fluoride (PVDF) with dimethyl acetamide (DMAc) and water. The curves on the phase diagram separate the regions of homogeneous mixtures, coexistence of two liquids, macroscopically uniform gels (swollen SC polymer) and coexistence of such gels with liquid. Using the plotted phase diagram, a new understanding of the NIPS mechanism was proposed and confirmed by direct microscopic observation of the NIPS process and SEM analysis of the membranes obtained following this way. An unexpected result of the study is discovery of the crystalline complexes in the mixtures of PVDF and DMAc, which was confirmed using both DSC and XRD techniques.

Carbon quantum dots (CQDs) were produced through citric acid (CA) pyrolysis. For the first time, we searched for the optimum CA pyrolysis duration and temperature. As a basic quality criterion of quantum dots, photoluminescence quantum yield (QY) was chosen. For this purpose, the pyrolysis products were analysed with UV-Vis spectroscopy and fluorescence (FL) spectroscopy. The optimum pyrolysis time was accepted to be 240 min, whereas the optimum pyrolysis temperature was approved as 200 & DEG;C. The pyrolysis products obtained at the optimum conditions were further subjected to dialysis. Finally, the purified CQDs were characterised with FL spectroscopy, transmission electron microscopy, dynamic light scattering, Raman spectroscopy, and Fourier transform infra-red spectroscopy. The produced CQDs were shown to be stable in water solution. Their PL QY (6.1%) was decreased to 1.2% after CQDs exposure to daylight for 90 days. Luminescent polymer composites were produced when CQDs were embedded in the poly(vinyl alcohol) and bacterial cellulose matrices. The prepared composites can be used for fabrication of transparent, flexible, and luminescent films and for production of anti-counterfeiting paper for confidential documents, labels, and banknotes.

To clarify the pathogenesis and molecular basis of ischemia-related nerve cell death, we examined the occurrence of DNA fragmentation as a hallmark of apoptotic cell death following incomplete ischemia in the rat brain by means of in situ end labeling of fragmented DNA, Incomplete ischemia was produced by permanently occluding one carotid artery, while temporarily occluding the other, The condensed nuclei of ischemic neurons in the neocortex, and in the subiculum and CA1 area of the hippocampus were positively stained 24 h and 3 days following vessel occlusion, respectively, and their morphology was typically apoptotic. The ischemic neurons with condensed nuclei gradually increased in number and were clearly stained for fragmented DNA in these areas. The labeled nuclei in the neocortex became pyknotic 72 h later, and in the hippocampus 7 days later incomplete ischemia. After attaining a peak, the number of labeled nuclei decreased with the duration of recovery in all areas. These results suggest that an apoptotic process plays, at least primarily, a role in the degeneration of neurons associated with incomplete forebrain ischemia in rat.

The effect of ultraviolet (UV) irradiation on gas permeability and mechanical properties of low-density polyethylene (LDPE) films was investigated in the temperature range from 20 degrees C to 60 degrees C. It was shown that UV exposure of the films resulted in their artificial aging, which is manifested as a decrease in gas permeability and as a variation in structure and mechanical properties of the LDPE films. A correlation between gas permeability and mechanical characteristics of the LDPE films subjected to the action of temperature and UV irradiation was found. The novelty of the performed investigations is due to the fact that the gas permeability of polymers exposed to the combined effects of UV radiation and temperature has not been studied so far.

High-density polyethylene (PE) swelling in organic solvents, orthodichlorobenzene and orthoxylene, was investigated. The PE specimen swelling kinetics was described with the first-order equation. For the first time, the PE specimen swelling rate constant was shown to decrease with increasing thickness of the specimens. The equilibrium PE specimen swelling was evaluated. It was found that equilibrium swelling independent of specimens’ thickness. PE specimen storage in organic solvents was shown to change its mechanical characteristics (tensile strength, Young’s modulus, and elongation at break) due to polymer plasticization. We showed that an increase in flexibility and elongation at break becomes noticeable after relatively short-term immersion of the PE specimens into these organic solvents. However, the tensile strength of swollen specimens remains enough high. The interaction between polymer chains and solvent molecules was not detected. The results obtained are important for design and operation of PE coatings and PE products, such as pipes, tanks, and other accessories subjected to contacts with oil products.

Molecular dynamics of a low-band gap polymer, poly{[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylheryl)carbonyl]thieno[3,4-b]thiophenediyl]} (PTB7), and its 1:1.5 wt blend with a fullerene derivative, [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM), accessible for organic photovoltaics was studied with the broadband dielectric spectroscopy (BDS) technique in a wide range of frequency (from 10(-1) to 10(6) Hz) and temperature (from -130 to 150 degrees C). In the BDS spectra, three types of molecular mobility of the polymer chains designated as gamma-, beta(1)-, and beta(2)-relaxations, along with conductivity and electrode polarization processes, were recognized, separated, and analyzed. The relaxation processes in PTB7 and PTB7:PC71BM were described with Arrhenius-type equations and related parameters were found. Their analysis allowed us to reveal the influence of the PC71BM molecules on the dynamics of the polymer chains. Based on dc conductivity data, the Cole-Cole diagrams for PTB7 and PTB7:PC71BM were plotted. They allowed for estimating the hole lifetime and its comparison with the hole extraction time.

Using a broadband dielectric spectrometry we studied the effect of carbon nanofillers (CN) with various aspect ratio (fullerene C60, multi-walled carbon nanotubes (MWCNT), reduced graphene oxide (rGO) and hybrid rGO:MWCNT nanofillers) on the electrical conductivity of the polyazomethine-based nanocomposites. One-dimensional MWCNTs with high aspect ratio were shown to be the most effective CN for fabrication of polymer-based nanocomposites with enhanced electrical conductivity.

The results of kinetic investigations of the orthodichlorbenzene and orthoxylene sorption by the high density polyethylene specimens of different thickness for 35 days are presented. It is shown that the sorption of solvents results in swelling of the polymer and its plasticization, which is expressed in changes in its mechanical characteristics such as ultimate strength, deformation to failure, and Young's modulus.

Poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4ʹ,7ʹ-di-2-thienyl-2ʹ,1ʹ,3ʹ-benzothiadiazole)] (PCDTBT) and its blend with [6,6]-phenyl C71-butyric acid methyl ester (PCBM) available for photovoltaic application were investigated with Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and broadband dielectric spectroscopy (BDS). In the BDS spectra, the molecular dynamics, polarization, and conductivity processes were identified, analyzed, and discussed for both PCDTBT and the PCDTBT/PCBM blend. The dielectric constant of the blend was successfully predicted when the dielectric constants of PCDTBT and PCBM and their weight ratio in the blend were taken into account. Enhanced dc conductivity due to increased charge carrier mobility was detected in the blend. The energetic offset of the photovoltaic blend under study was shown to be directly estimated from the BDS data.

We prepared the polyazomethine/MWCNTs nanocomposites varying in the nanofiller loading (from 0 to 1.5 wt %). Taking into account an upshift of the characteristic D and G bands of MWCNTs in the Raman spectrum of the nanocomposite, we confirmed the interfacial interactions between MWCNTs and polymer chains. When we studied the nanocomposites morphology, we concluded that both disentanglement and dispersion of MWCNTs in the polymer matrix are provided by interfacial interactions. Using broadband dielectric spectroscopy technique, we investigated the interfacial polarization in the nanocomposites. We found that this phenomenon is valuable for electrical conductivity of the nanocomposites with high MWCNTs loading, particularly, at high temperatures and low frequencies.

We produced nanocomposites comprised of polyazomethine and reduced graphene oxide by solution mixing. The nanofiller concentration ranged from 0.25 to 1.5 wt.%. Both neat polymer and nanocomposites samples were investigated using broadband dielectric spectrometry under the same conditions. The electrical conductivity s of the samples was examined as a complex value being a combination of two parameters: dc conductivity (sigma(dc)) and ac conductivity (sigma(ac)). The temperature dependences of sigma(ac) were found to follow the Arrhenius equation, whereas the frequency dependences of sigma(ac) were shown to obey a power law. We proposed that the correlated barrier hopping could explain behaviour of sigma(ac) of the nanocomposites under study.

The polyazomethine/hybrid carbon nanofillers composites were fabricated. The nanofilles were comprised of thermally reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs) varying in rGO:MWCNTs ratio; the total nanofillers loading was 1 wt%. The scanning electron miscroscopy images revealed uniform distribution of the hybrid nanofillers and formation of 3D networks between rGO and MWCNTs. Molecular dynamics of the polymer chains in these nanocomposites was investigated with broadband dielectric spectroscopy. The polymer fragility, the dielectric glass transition temperature, and the dielectric relaxation strength of the nanocomposites were evaluated and analyzed depending on the rGO:MWCNTs ratio. The thermal glass transition temperature and the thermal relaxation strength evaluated from the differential scanning calorimetry data were shown to behave in other manner. This behavior was interpreted in terms of a fraction of polymer being immobilized in an interfacial layer around the nanoparticles.

Using solution blending method, we produced nanocomposites based on polyazomethine (PAZ) loaded with hybrid carbon nanofillers. The nanofillers comprised reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs). The total nanofiller loading was equal to 1 wt% while the rGO:MWCNTs ratio varied as follows: 100:0, 75:25, 50:50, 25:75, and 0:100 wt%: wt%. The complex dielectric permittivity data obtained with a broadband dielectric spectrometer were used to analyze electrical conductivity of the nanocomposites in wide ranges of frequency and temperature. Electrical conductivity was found to increase with increasing MWCNT sportion and its maximum value was achieved when the nanofiller contained the MWCNT snanoparticles exclusively. We extracted the electrical conductivity components, dc conductivity sigma(dc) and ac conductivity sigma(ac), and analyzed their behavior as function of frequency and temperature. The temperature dependences of sigma(ac) were described with the Arrhenius equation, whereas its frequency dependences were characterized with a power function. For explaining the sac behavior, the correlated barrier hopping mechanism was accepted. Interfacial interactions between the hybrid nanofillers and the polymer matrix (the Maxwell-Wagner-Sillars effect) were detected. It was found to be strongly pronounced in the nanocomposites with high portion of MWCNTs in the hybrid fillers.

Incompatible blends of cellulose acetate butyrate (CAB) and copolymer of ethylene, acrylic ester, and maleic anhydride (PE-Acr-MA) with a component ratio 70/30 vol% were prepared by melt extrusion at the rates of 150 and 500 rpm.The goal was to modify weak impact properties of CAB.We showed that at a speed of 500 rpm, both small individual (0.9 μm in diameter) and large coalesced (2.3 μm in diameter) particles of the PE-Acr-MA phase were formed; the impact strength of the blend increased in 6.5 times as compared with that of pure CAB.However, at a melt mixing rate of 150 rpm, the size of the individual PE-Acr-MA particles decreased in 3.8 times, whereas that of the coalesced particles diminished by 6.6 times; the impact strength of the blend increased in about 40 times as compared with that of pure CAB and reached the values around and higher than 70 kJ/m 2 .The effect of the screw rotating speed on viscoelastic properties of each component and their viscosity ratio was analyzed and shown to control blend morphology and mechanical properties.