Search Results (109)

Polymeric nanoparticles based on poly(ethyl cyanoacrylate) (PECA) and poly(ε-caprolactone) (PCL) were synthesized via semicontinuous microemulsion polymerization for potential biomedical applications. A systematic evaluation of four surfactants (Tween 80, Alkonat L70, Genapol LRO, and Brij-20) was carried out to determine their effects on micelle formation and particle size. Brij-20 enabled the formation of nanoparticles under 100 nm, with optimal conditions identified at 4% surfactant concentration and pH 1.75. The polymerization process included acid-catalyzed ring-opening of ε-caprolactone, followed by the semicontinuous addition of ethyl-2-cyanoacrylate under an inert atmosphere. Copolymerization was confirmed through FT-IR spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and differential scanning calorimetry, revealing a glass transition temperature (T_g) of 110.9 °C, indicating PECA as the dominant phase. Thermogravimetric analysis showed two decomposition events corresponding to each polymer. Transmission electron microscope analysis revealed nanoparticles averaging 51.74 nm in diameter. These findings demonstrate the feasibility of producing PECA-PCL nanoparticles with controlled size and composition, suitable for drug delivery and other biomedical uses. Full article

Magnetorheological (MR) fluids are frequently reported to have potential as lubricants for hydrodynamic bearings operating at high loads, but no comprehensive effort has been made to investigate their performance under a variety of operating conditions. This paper, therefore, presents an extensive experimental and numerical investigation of an MR-lubricated hydrodynamic journal bearing subjected to different loads and magnetic fields, and compares these results to those of an oil-lubricated bearing. It is shown that by increasing the magnetic field strength, the performance characteristics of the bearing can be changed from low hydrodynamic friction and a high transition speed to high hydrodynamic friction and a low transition speed. Furthermore, it was found that the way in which these characteristics scale with increasing load differs for the MR- and oil-lubricated bearings. With MR lubrication, the relative change in characteristics with the application of a magnetic field is smaller at higher loads, due to the strong shear-thinning rheology of MR fluids. To include these effects in the model, a basic relation for the apparent MR viscosity as a function of shear rate, temperature, and magnetic field strength is introduced. Finally, the bearing was made from a polymer to improve wear resistance under MR lubrication, but a comparison with a Reynolds equation-based numerical model indicates possible performance degradation due to shape errors, which is a known issue with this bearing material. Full article

A new poly(azomethine) with improved solubility was successfully prepared by the polycondensation of terephthalaldehyde and 2,2-Bis[4-(4-aminophenoxy)phenyl]-hexafluoropropane (4-BDAF) under green chemistry conditions. This new polymer containing hexafluoroisopropylidene was compared with a polymer containing isopropylidenediphenyl to study the influence of the presence of fluorine atoms on the properties of the polymer. Both were characterized by nuclear magnetic resonance (NMR), their molecular weight was measured by gel permeation chromatography (GPC), and their morphology was studied by X-ray diffraction (XRD). The two polymers obtained were soluble in most polar aprotic solvents and even in less polar solvents, which are practical and easily accessible solvents. Their thermal properties were determined by a thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). These two new polymers showed high resistance to thermal decomposition up to 490 °C, with a glass transition temperature (Tg) of 180 °C. The photophysical properties were studied by UV/Visible absorption. The polymers were doped and then deposited on cellulose filaments, an approach that made it possible to produce self-supporting conductive composites thanks to their mechanical properties. The topography of the resulting materials was characterized at submicron scales before estimating their electronic conductivity and gap energy by diffuse reflection spectroscopy. Full article

The precise and deterministic integration of fluorescent emitters with photonic nanostructures is an important challenge in nanophotonics and key to the realization of hybrid photonic systems, supporting effects such as emission enhancement, directional emission, and strong coupling. Such integration typically requires the definition or immobilization of the emitters at defined positions with nanoscale precision. While various methods were already developed for creating localized emitters, in this work we present a new method for the deterministic fabrication of fluorescent nanostructures featuring well-defined optical transitions; it works with a minimal amount of steps and is scalable. Specifically, electron-beam lithography is used to directly pattern a mixture of the negative-tone electron-beam resist with the europium complex Eu(TTA)₃, which exhibits both electric and magnetic dipolar transitions. Crucially, the lithography process enables precise control over the shape and position of the resulting fluorescent structures with a feature size of approx. 100 $\mathrm{n}$$\mathrm{m}$. We demonstrate that the Eu(TTA)₃ remains fluorescent after exposure, confirming that the electron beam does not alter the structure the optical transitions. This work supports the experimental study of local density of optical states in nanophotonics. It also expands the knowledge base of fluorescent polymer materials, which can have applications in polymer-based photonic devices. Altogether, the presented fabrication method opens the door for the realization of hybrid nanophotonic systems incorporating fluorescent emitters for light-emitting dielectric metasurfaces. Full article

Cobaltocenium-containing (co)polysiloxanes (Cc-PDMSs) with terminal and side groups were synthesized by the reaction of catalyst-free hydroamination between ethynylcobaltocenium hexafluorophosphate and polysiloxanes comprising amino moieties as terminal and side groups. The conversion of NH₂ groups in the polymers reaches 85%. The obtained (co)polysiloxanes “gelate” due to an increase in their molecular weight by approx. 30 times, when stored at room temperature over one week. “Gelated” Cc-PDMSs remain soluble in most polar solvents. The structure of Cc-PDMSs and the mechanism of “gelation” were established by ¹H, ¹³C{¹H}, ²⁹Si{¹H}, ¹⁹F{¹H}, ³¹P{¹H} nuclear magnetic resonance, infrared, ultraviolet–visible, and X-ray photoelectron spectroscopies. As determined by cyclic voltammetry, Cc-PDMSs possess redox properties (Co^II/Co^III transitions at E_1/2 = −1.8 and −1.3 V before and after “gelation”, respectively). This synthetic approach allows to increase the molecular weights of the synthesized polysiloxanes functionalized with cobaltocenium groups easily, leading to their higher film-forming ability, which is desirable for some electronic applications. Cc-PDMSs can be utilized as redox-active polymer films in modified electrodes, electrochromic devices, redox-active coatings, and components for batteries. Full article

Polyimides (PIs) have been extensively used in thin film and micro-electromechanical system (MEMS) processes based on their excellent thermal and mechanical stability and high glass transition temperature. This research explores the development of a novel multilayer and multifunctional polymer composite electro-piezomagnetic device that can function as an energy harvester or sensor for current-carrying wires or magnetic field sensing. The devices consist of four layers of composite materials with a polyimide matrix. The composites have various nanoparticles to alter the functionality of each layer. Nanoparticles of Ag were used to increase the electrical conductivity of polyimide and act as electrodes; lead zirconate titanate was used to make the piezoelectric composite layer; and either neodymium iron boron (NdFeB) or Terfenol-D was used to make the magnetic and magnetostrictive composite layer, which was used as the proof mass. A novel all-polymer multifunctional polyimide composite cantilever was developed to operate at low frequencies. This paper compares the performance of the different magnetic masses, shapes, and concentrations, as well as the development of an all-magnetostrictive device to detect voltage or current changes when coupled to the magnetic field from a current-carrying wire. The PI/PZT cantilever with the PI/NdFeB proof mass demonstrated higher voltage output compared to the PI/Terfenol-D proof mass device. However, the magnetostrictive composite film could be operated without a piezoelectric film based on the Villari effect, which consisted of a single PI-Terfenol-D film. The paper illustrates the potential to develop an all-polymer composite MEMS device capable of acting as a magnetic field or current sensor. Full article

Transition metal oxides have been widely used in microwave-absorbing materials, but how to improve impedance matching is still an urgent problem. Therefore, we introduced urea as a polymer carbon source into a three-dimensional porous structure modified by Co₃O₄ nanoparticles and explored the influence of different heat treatment temperatures on the wave absorption properties of the composite. The nanomaterials, when calcined at a temperature of 450 °C, exhibited excellent microwave absorption capabilities. Specifically, at an optimized thickness of 9 mm, they achieved a minimum reflection loss (RL_min) of −97.3 dB, accompanied by an effective absorption bandwidth (EAB) of 9.83 GHz that comprehensively covered both the S and Ku frequency bands. On the other hand, with a thickness of 3 mm, the RL_min was recorded as −17.9 dB, with an EAB of 5.53 GHz. This excellent performance is attributed to the multi-facial polarization and multiple reflections induced by the magnetic loss capability of Co₃O₄ nanoparticles, the electrical conductivity of C, and the unique three-dimensional structure of diatomite. For the future development of bio-based microwave absorption, this work provides a methodology and strategy. Full article

The development of efficient sensors able to detect alcoholic compounds has great relevance in many fields including medicine, pharmaceuticals, food and beverages, safety, and security. In addition, the measurements of alcohols in air are significant for environmental protection because volatile alcohols can have harmful effects on human health not only through ingestion, but also through inhalation or skin absorption. The analysis of alcohols in breath is a further expanding area, being employed for disease diagnoses. The analyses performed by using chromatography, mass-spectrometry, nuclear magnetic resonance, ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, or Raman spectroscopy often require complex sampling and procedures. As a consequence, many research groups have focused their efforts on the development of efficient portable sensors to replace conventional methods and bulky equipment. The ability to operate at room temperature is a key factor in designing portable light devices suitable for in situ real-time monitoring. In the present review, we provide a survey of the recent literature on the most efficient chemiresistive materials for alcohol sensing at room temperature. Remarkable gas-sensing performances have mainly been obtained by using metal oxides semiconductors (MOSs), metal organic frameworks (MOFs), 2D materials, and polymers. Among 2D materials, we mainly consider graphene-based materials, graphitic carbon nitride, transition metal chalcogenides, and MXenes. We discuss scientific advances and innovations published in the span of the last five years, focusing on sensing mechanisms. Full article

The biaxially-oriented PA56/512 has excellent mechanical strength, extensibility and water–oxygen barrier properties and has broad application prospects in green packaging, lithium battery diaphragm and medical equipment materials. The correlation between the aggregation structure evolution and macroscopic comprehensive properties of copolymer PA56/512 under biaxial stretching has been demonstrated in this work. The structure of the random copolymerization sequence was characterized by ¹³C Nuclear magnetic resonance (NMR). The typical isodimorphism behavior of the co-crystallization system of PA56/512 and its BOPA-56/512 films was revealed by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) tests. And the aggregation structure, including the hydrogen bond arrangement, crystal structure and crystal morphology of PA56/512 before and after biaxial stretching, was investigated by XRD, Fourier-transform infrared spectroscopy (FTIR) and polarized optical microscopy (POM) tests. Furthermore, the effect of the biaxially-oriented stretching process on the mechanical properties of PA56/512 has been demonstrated. In addition, a deep insight into the influence of the structure on the crystallization process and physical–mechanical performance has been presented. The lowest melting point at a 512 content of 60 mol% is regarded as a “eutectic” point of the isodimorphism system. Due to the high disorder of the structural units in the polymer chain, the transition degree of the folded chain (gauche conformation) is relatively lowest when it is straightened to form an extended chain (trans conformation) during biaxially-oriented stretching, and part of the folded chain can be retained. This explains why biaxially stretched PA56/512 has high strength, outstanding toughness and excellent barrier properties at the pseudo-eutectic point. In this study, using the unique multi-scale aggregation structure characteristics of a heterohomodymite polyamide at the pseudo-eutectic point, combined with the new material design scheme and the idea of biaxial-stretching processing, a new idea for customized design of high-performance multifunctional polyamide synthetic materials is provided. Full article

Modern science and technology demand a low glass transition temperature, yet one tailored to specific thermoset needs and specific to individual hardener applications. Two novel, nonterminal liquid crystalline epoxy resins (LCER) were synthesised, with their structures characterized via nuclear magnetic resonance (NMR), mass spectrometry (MS), and elemental analysis. Their liquid crystalline nature and thermal properties were determined using polarized optical microscopy (POM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). A set of seven aromatic amines serving as curing agents was used to perform curing in fourteen different systems in order to assess the glass transition temperature (T_g) of the obtained polymer networks using DSC. The liquid crystalline elastomers were obtained with vitrification occurring in a low temperature range (−10–40 °C), with a more predictable outcome for amines with two aromatic rings in the structure than with one. Moreover, the resin with a core consisting of four aromatic rings produces networks with higher T_g than the three-aromatic resin. The use of nonterminal LCER allowed the lowering of the glass transition temperature of the polymers to more than 70 °C compared to a terminal analogue. This brings new possibilities of designing highly elastic yet cured polymers with potential for use in smart applications due to the LC nature of the resin. Full article

It is commonly acknowledged that polymer composites in service are often subjected to not only intricate mechanical loads but also harsh environmental conditions. The mechanical and thermal properties of five particular composites are explored here. The composites are composed of laminates of glass cloth type “E” sheet infilled with a duroplastic matrix. This is a thermoset polymer—epoxy resin with different molecular weights. The composites were fabricated by IZOERG company, which is based in Poland. The final articles were 1.5 mm thick by 60 cm long and 30 cm wide, with the glass layers arranged parallel to the thickness. Young’s modulus and tensile strength were measured at room temperature. Using the thermal analysis of dynamic mechanical properties (DMTA), the values of the storage modulus and the loss modulus were determined, and the damping factor was used to determine the glass transition temperature (Tg). It was revealed that the nature of changes in the storage modulus, loss modulus, and damping factor of composite materials depends on the type of epoxy resin used. Thermal expansion is a crucial parameter when choosing a material for application in cryogenic conditions. Thanks to the TMA method, thermal expansion coefficients for composite materials were determined. The results show that the highest value of the coefficient of thermal expansion leads the laminate EP_4_2 based on brominated epoxy resin cured with novolac P. Duroplastic composites were characterized at cryogenic temperatures, and the results are interesting for developing cryogenic applications, including electric motors, generators, magnets, and other devices. Full article

This paper addresses a range of environmental issues stemming from the improper disposal of construction waste and its low recycling rate by examining the effects and mechanisms of polyvinyl alcohol (PVA) solution in modifying recycled aggregates. Basic physical properties, energy-dispersive spectroscopy (EDS), X-Ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to study these effects and mechanisms. Tests on basic mechanical properties were performed to assess the impact of aggregate modification and the brick-concrete ratio on recycled brick-aggregate concrete’s mechanical characteristics. Nuclear magnetic resonance and microhardness tests were performed to analyze the influence exerted by PVA modification on the interfacial transition zone (ITZ), microstructure, and pore structure, thus exploring the connection between modified recycled-brick-aggregate concrete’s microstructure and its icromechanical properties. The findings show that the water absorption and crushing index of recycled aggregates (RA) immersed in a 10% PVA solution for 24 h decrease significantly, while the apparent density increases most notably. This phenomenon can be ascribed to the development of a PVA coating on the exterior of the reused aggregates. The optimal mechanical properties for recycled brick aggregate concrete (RAC) occur when the replacement rate is 30% and the brick-concrete ratio is 1:1. The compressive strength is 44.2 MPa, the bending strength is 15.6 MPa, and the splitting tensile strength is 3.85 MPa. Additionally, the modification with PVA results in a higher percentage of transition pores, while simultaneously reducing the percentage of macropores. There is an uptick in the frequency of harmless and less harmful pores, and a declining proportion of harmful and more harmful pores. The ITZ’s structural morphology in the RAC is effectively improved by the coating structure formed through the bonding of the polymer with cement hydration products, and PVA modification reduces the thickness of this zone. Full article

A set of polyphenylene oxides incorporating DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) functionality, denoted as DOPO−R−PPO, was synthesized by copolymerization of 2,6-dimethylphenol (2,6-DMP) with various DOPO-substituted tetramethyl bisphenol monomers. In the initial step, a Friedel–Crafts acylation reaction was employed to react 2,6-DMP with different acyl chlorides, leading to the formation of ketone derivatives substituted with 2,6-dimethylphenyl groups. Subsequently, the ketones, along with DOPO and 2,6-DMP, underwent a condensation reaction to yield a series of DOPO-substituted bisphenol derivatives. Finally, polymerizations of 2,6-dimethylphenol with these DOPO-substituted bisphenols were carried out in organic solvents using copper(I) bromide/N-butyldimethylamine catalysts (CuBr/DMBA) under a continuous flow of oxygen, yielding telechelic PPO oligomers with DOPO moieties incorporated into the polymer backbone. The chemical structures of the synthesized compounds were characterized using various analytical techniques, including Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H NMR), phosphorus nuclear magnetic resonance (³¹P NMR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). When compared to conventional poly(2,6-dimethyl-1,4-phenylene oxide)s with a similar molecular weight range, all DOPO−PPOs exhibited higher glass transition temperatures, enhanced thermal degradability, and increased char yield formation at 800 °C without compromising solubility in organic solvents. Full article

The metal–radical approach is a well-established synthetic way toward multi-spin systems that relies on the coordination of stable radical ligands with transition metal ions. The advantage offered by the use of paramagnetic ligands is that metal–radical magnetic exchange coupling is direct between the magnetic orbitals of the radical and metal ion. With the aim of further exploring this approach, crystals of four heterspin complexes, [M(hfac)₂L^F]₂ {M = Mn, Co, or Ni and hfac = hexafluoroacetylacetonate} and [Cu(hfac)₂L^F]_n, were obtained using a new fluorinated pyrazolyl-substituted nitronyl nitroxide radical, 4,4,5,5-tetramethyl-2-(5-fluoro-1-methyl-1H-pyrazol-4-yl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L^F) as a ligand. The newly synthesized complexes were fully characterized, including X-ray crystallography and magnetometry. XRD analysis revealed that complexes [M(hfac)₂L^F]₂ have similar dimer structures in which a metal ion is in a six-coordinated environment with four O atoms from the two hfac ligands, one radical O atom, and one pyrazole N atom from ligand L^F. Nonetheless, the packing patterns of the complexes were found to be considerably different. In [Mn(hfac)₂L^F]₂, there are no magnetically important short contacts between manganese dimers. By contrast, in [Co(hfac)₂L^F]₂ and [Ni(hfac)₂L^F]₂, there are short contacts between non-coordinate O atoms of nitronyl nitroxide moieties. Magnetic behaviors of [M(hfac)₂L^F]₂ showed that the M ions and the directly coordinated radicals are strongly antiferromagnetically coupled (J_Mn-ON = −84.1 ± 1.5 cm⁻¹, J_Co-ON = −134.3 ± 2.6 cm⁻¹, and J_Ni-ON = −276.2 ± 2.1 cm⁻¹; $\widehat{H}=-2J{\widehat{\stackrel{⃑}{S}}}_{\mathrm{M}}{\widehat{\stackrel{⃑}{S}}}_{\mathrm{N}\mathrm{O}}$). Notably, the magnetization of [Mn(hfac)₂L^F]₂ having molecular structure proved to be accompanied by hysteresis. The [Cu(hfac)₂L^F]_n complex has a chain-polymer structure with alternating magnetic fragments: three spin exchange clusters {O_NO–Cu(II)–O_NO} and {Cu(II)} ions. Despite the direct coordination of radicals, its magnetic properties are weakly ferromagnetic (J_Cu-ON = 14.8 ± 0.3 cm⁻¹). Full article

Magnetic polymer composites have recently attracted considerable interest, primarily because of their promising applications, especially in the biomedical industry. The aim of this study is to investigate the impact of ultraviolet C (UVC) irradiation as a disinfection method on the mechanical characteristics of composite polymer magnets. Tensile and compression tests were conducted following the standards set by ASTM D3039 and ASTM D3410, respectively. In addition, energy dispersive spectroscopy (EDS) was used to determine the effect of the disinfection method on the amount of carbon, oxygen, and iron within the surface of the composite polymer magnet material. The UVC’s irradiation impact was statistically assessed by a t-test. The results of the tensile tests demonstrated a significant increase in the transition force, measuring 0.41 kN and 0.58 kN before and after UVC exposure, respectively. Similarly, the outcomes of the compression tests showed a notable increase in yield force, registering 4.9 kN and 6 kN before and after UVC treatment. This suggests that the composite magnetic material has gained a higher capacity to withstand compressive loads than tensile loads. Finally, the EDS analysis revealed the carbon mass percentage was 71.69% prior to UVC radiation exposure, with it increasing to 78.56%, following exposure. This suggests that the composite material exhibited improved hardness. These findings highlight that UVC irradiation has a beneficial impact on both the mechanical and chemical properties of the composite magnet material, which support its use as a disinfection method in clinical settings. Full article