Synthesis and characterization of new imidazole and fluorene–bisphenol based polyamides: Thermal,photophysical and antibacterial properties

A new para-linked diether-diamine, 9,9-bis{4-[2-(4,5-diphenylimidazol-2-yl)-4-aminophenoxy] phenyl}fluorene (III), bearing fluorene–bisphenol and two ortho-linked diaryl-substituted imidazole rings were synthesized by the catalytic reduction of the nitro groups of compound (II), 9,9-bis{4-[2-(4,5-diphenylimidazol-2-yl)-4-nitrophenoxy]phenyl}fluorene, by using hydrazine monohydrate in the presence of Pd/C. Compound (II) was synthesized by the nucleophilic chloro displacement reaction of the synthesized 2-(2-chloro-5-nitrophenyl)-4,5-diphenyl-1H-imidazole with 9,9-bis(4-hydroxyphenyl)fluorene in refluxing DMAc in the presence of potassium carbonate. This diamine was condensed directly with aliphatic and aromatic diacids via the Yamazaki–Higashi phosphorylation method in the presence of triphenylphosphite (TPP), pyridine (Py) and halide salt to give high molecular polyamides (PAs). The synthesized PAs were obtained in quantitative yields with inherent viscosities between 0.51 and 0.76 dL g^?1. The structures of diamine and PAs were characterized by elemental analysis, FT-IR and NMR spectroscopy, and properties of PAs were investigated by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and UV–visible and fluorescence spectroscopy. The PAs showed good solubility in aprotic and polar organic solvents, with high thermal stability exhibiting the glass transition temperatures (T_gs) and 10% weight loss temperatures (T_10%) in the range of 226–330 °C and 400–466 °C in air, respectively, and fluorescence emission with maximum wavelengths (λ_em) in the range of 417–473 nm with quantum yields (Φ_f) of 9–35%. Two of these polymers together with compounds (II) and (III) were also screened for antibacterial activity against Gram positive and Gram negative bacteria.     

Characterization of Mechanical and Thermal Properties of Vinyl-ester/TiO2 Nanocomposites Exposured to Electron Beam

The effect of electron beam irradiation (EBI) on the properties of vinyl-ester/TiO₂ nanocomposites has been studied in the present paper. The nanoparticles (1, 3 and 5 wt%) in the matrix are dispersed by high shear matrix characterized by transition electron microscopy. Neat polymer and nanocomposites were exposed to EBI in 100, 500 and 1,000 kGy doses. The mechanical, thermal behaviors of nanocomposites were studied by tensile and flexural tests and thermo-gravimetric analysis. The results showed that irradiation improved the properties of neat resin and nanocomposies. Fourier transform spectroscopy spectra showed that VE and nanocomposite are stable against of irradiation of EBI up to 1,000 kGy.     

A new method for joint estimation of delay and Doppler from ambiguity function: combination of stochastic process and spatial processing for noise and clutter suppression

In this article, a new method is introduced for joint delay and Doppler estimation in ambiguity function (AF)-based radars. In this method, first each cell of AF is considered as a random variable and then a stochastic process is estimated for each cell based on its values during consecutive radar scans. In the second step, the AF is divided to high probability target and high probability clutter zones using parameters of the estimated stochastic processes. Finally, exact values of delay and Doppler of radar targets are extracted and localised from the divided AF by employing spatial processing techniques. Performance of the proposed method is evaluated in two different scenarios, corresponding to high and low speed targets, respectively. The obtained results show the greater ability of the suggested method in detection of the above types of targets compared to the present approaches. Furthermore, it can be shown that the proposed method causes more considerable improvement in the detection of low speed targets than high speed targets compared to available methods.     

Low-voltage low-power Gm-C filters: a modified configuration for improving performance

In this paper, after addressing the effect of finite output impedance of Gm cells on the performance of Gm-C filters, a modified configuration suitable for low-voltage operation is presented. In the proposed architecture, to efficiently increase the output impedance, body-driven impedance boosting is employed. The circuit-level topology of Gm cells is modified in order to increase the output impedance with minimized power consumption. To show the effectiveness of the proposed scheme, a 0.9-V 5-th order Butterworth low-pass filter with 8 MHz cutoff frequency is designed and simulated in 90-nm CMOS technology. Employing the proposed technique, power consumption is reduced from 0.7 mW to 0.5 mW.     

Thermoelectric composite structure with desirable mechanical properties for high-performance multi-functional applications

Thermoelectric (TE) structures based on energy harvesting technology have played a vital role in wide-reaching applications. In this study, a composite structure consisting of a glass fabric covered with a nanocomposite membrane (polyacrylonitrile [PAN]/carbon nanotube [CNT]/copper oxide nanoparticle [CuO]) was prepared to provide thermoelectric conversion. The performance of the TE composite structure was evaluated by analyzing the mechanical properties, thermoelectric properties, and the ability of the structure to power small electronic equipment. The results showed that the nanocomposite membrane was effective in improving the electrical properties, whereas the glass fabric could significantly suppress the thermal conductivity. The results suggest that the glass fabric covered with nanocomposite fibers containing nanofillers (15 wt% CNT & 15 wt% CuO) has a high potential to enhance the resistance against external force by 56% on average, compared to the uncovered glass fabric. Besides the power factor of the TE composite structure can reach up to 19.61 μW m⁻¹ K⁻², which can power an output voltage of 3.2 V at a temperature difference from 20 to 80°C.     

Dummy template molecularly imprinted polymer for omeprazole and the study of its drug binding and release properties

In this study, we tried to prepare an omeprazole (OMP)‐imprinted polymer and study its binding and release properties in an aqueous media. Because of the instability of OMP under polymerization conditions and the inability of the molecule to form effective interactions with monomers, pantoprazole (PANTO) was used as a dummy template for the imprinting process. Different monomers and solvents were evaluated in polymerization. The optimized imprinted polymer was prepared in chloroform as a porogen. Also, 4‐vinylpyridine and ethylene glycol dimethacrylate were selected as a functional monomer and a crosslinker, respectively. The optimized imprinted polymer was evaluated in a binding study. The binding and release properties of the polymer were then investigated at different pHs. Our data indicated a higher affinity of the imprinted polymer to PANTO and OMP than that of nonimprinted polymer (NIP). The maximum percentage of OMP released from the imprinted polymer was 36–41%, whereas that for the NIP was 74–85%. These data were related to the 38–43 and 29–34 μg of OMP released from the imprinted polymer and NIP, respectively. Also, the protective effect of the imprinted polymer for OMP at pH 2 was greater than that of the nonimprinted one. This study revealed that the dummy template molecular imprinting was an effective method for preparing selective imprinted cavities in a polymeric matrix, especially for the molecules that were unstable during polymerization or unable to establish effective bonds with the monomers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4165–4170, 2013     

Assessment of intertube interactions in different functionalized multiwalled carbon nanotubes incorporated in a phenoxy resin

In this work, about 1 wt% of different functionalized carbon nanotubes (CNTs), namely CNT? COOH (CNT with carboxylic groups), CNT? NH₂ (CNT with amine groups) and CNT? OH (CNT with hydroxyl groups), as well as nonfunctionalized CNTs were incorporated into a phenoxy resin via a melt mixing process. The extent of intertubes and polymer–tubes interactions and their influence on state of CNTs dispersion were assessed through determination of electrical, rheological, and morphological characteristics. CNT? NH₂ showed the lowest intertubes interactions followed by CNT? OH and CNT? COOH. Nanocomposite made from CNT? COOH showed the poorest state of CNTs dispersion and the biggest CNTs agglomerates and it remained nonconductive. The acid‐functionalized CNTs were not able to form strong polymer–tube interactions because of their high cohesive energy and therefore in the melt rheological investigations they exhibited the lowest storage modulus and complex viscosity as well as the highest loss factor among all the studied CNTs. A good balance between intertubes and polymer–tube interactions is necessary through proper selection of CNTs functional groups for achieving a good state of CNTs dispersion and consequently obtaining enhanced electrical and viscoelastic properties. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Cellulose acetate butyrate membrane containing TiO2 nanoparticle: Preparation, characterization and permeation study

Cellulose acetate butyrate/TiO₂ hybrid membranes were prepared via phase inversion by dispersing the TiO₂ nanoparticles in casting solutions. The influence of TiO₂ nanoparticles on the morphology and performance of membranes was investigated. The scanning electron microscope images and experiments of membrane performance showed that the membrane thickness and pure water flux were first increased by adding the TiO₂ nanoparticles to the casting solution up to 4 wt% and then decreased with the addition of further nanoparticles to it. The obtained results indicated that the addition of TiO₂ in the casting solution enhanced the rejection and permeate flux in filtration of bovine serum albumin solution. Furthermore, increasing the TiO₂ nanoparticle concentration in the casting solution increased the flux recovery and consequently decreased the fouling of membrane.     

Photocatalytic degradation of ammonia by light expanded clay aggregate (LECA)-coating of TiO2 nanoparticles

Photocatalytic degradation of ammonia on supported TiO₂ nanoparticles was investigated. The TiO₂ nanoparticles used as photocatalyst were coated on light expanded clay aggregate granules (LECA), which is a porous and light weight support. Photocatalytic reaction activity of prepared catalyst was determined by ammonia degradation from water synthetically polluted with ammonia. Experiment results showed significantly high photocatalytic activity for the immobilized catalysts. The ammonia was removed more than 85% within 300 min of the process with optimum calcinations temperature 550 °C and pH 11. Kinetics of the photocatalytic reaction followed a pseudo-first order model. XRF, XRD and SEM analyses revealed a rather uniform coating of TiO₂ on the support. By using floated TiO₂/LECA as a photocatalyst in aqueous solution of NH ₃ ^? , the ammonia was photodegraded into N₂ and H₂ gases, while NO ₂ ^? and NO ₃ ^? were formed at very low concentrations.     

Characterization and comparative evaluation of polysulfone and polypropylene hollow fiber membranes for blood oxygenators

Blood oxygenators are used to saturate oxygen levels and remove carbon dioxide from the body during cardiopulmonary bypass. Although the natural lung is hydrophilic, commercially used oxygenator materials are hydrophobic. Surface hydrophobicity weakens blood compatibility, as long-term contact with the blood environment may lead to different degrees of blood activity. Polysulfone may be considered an alternative hydrophilic material in the design of oxygenators. Therefore, it may be directed toward developing hydrophilic membranes. This study aims to investigate the feasibility of achieving blood gas transfer with a polysulfone-based microporous hollow fiber membrane and compare it with the commercially available polypropylene membranes. Structural differences in the membrane morphology, surface hydrophilicity, tortuosity, mass transfer rate, and material properties under different operation conditions of temperature and flow rates are reported. The polysulfone membrane has a water contact angle of 81.3°, whereas a commercial polypropylene membrane is 94.5°. The mass transfer resistances (s/m) for the polysulfone and polypropylene membranes are calculated to be 4.8 × 10⁴ and 1.5 × 10⁴ at 25°C, respectively. The module made of polysulfone was placed in the cardiopulmonary bypass circuit in parallel with the commercial oxygenator, and pH, pO₂, pCO₂ levels, and metabolic activity were measured in blood samples.