Microstructural study of synthesized polyethylenes by homogeneous and heterogeneous nickel α-diimine catalysts

In this work, ethylene polymerization was investigated by using homogeneous and heterogenouse nickel α-diimine catalysts [1,4-bis(2,6-diisopropylphenyl) acenaphthene diimine nickel(II) dibromide]. Methyl aluminoxane (MAO) and triethyl aluminum (TEA) were used as cocatalysts in homogenous and heterogeneous polymerizations, respectively. The heterogeneous catalyst showed lower activity than its homogeneous equivalent. The influence of polymerization temperature and heterogenization conditions was studied on the microstructure properties of the prepared polymers. Increasing polymerization temperature (T _P) up to 50 °C decreased the activity of both homogenous (LN) and heterogeneous (LNS) nickel α-diimine catalysts. The highest activities were 1286 and 982 kg PE (mol Ni bar h)^?1 obtained at T _P = 30 °C for LN and LNS catalysts, respectively. The polymer samples obtained by supported catalyst (LNS) showed lower unsaturation contents. Moreover, DSC analysis did not show any melting peaks for polymers obtained by LN catalyst due to their amorphous structure, which was confirmed by XRD analysis. The microstructure of the prepared polymers was completed by successive self-nucleation annealing (SSA) and was investigated by ¹³C NMR studies. The SSA thermogram of samples made by LNS catalyst exhibited several crystal types with different lamella thicknesses. The branches in polyethylene samples produced by homogenous catalyst were higher and showed more diversity. The total methyl branch percentages for both LN and LNS catalysts were 13.1 and 3.4%, respectively.     

Green bio-synthesis of Ni/montmorillonite nanocomposite using extract of Allium jesdianum as the nano-catalyst for electrocatalytic oxidation of methanol

In this work, synthesis of Ni nanoparticles was carried out successfully by water extract of Allium jesdianum as a biochemical reducing agent in the presence of montmorillonite clay (MMT) as a natural solid support for the first time. Then the electrochemical activity of the synthesized nanocomposite was investigated in methanol electrocatalytic oxidation. MMT with high cation exchange capacity and nano layer structure was exposed to ion exchange conditions in nickel solution. Then Ni²⁺ ion exchanged form was used in this process as a source of ions and also capping agent. Water extract of Allium jesdianum used as a reducing agent due to abundant availability of phenolic and flavonoid contents. The synthesized Ni/MMT nanocomposite was characterized using UV–Vis spectroscopy (UV–Vis), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission electron microscopy (TEM) and Energy-dispersive X-ray spectroscopy (EDX). The surface of prepared modified electrode has been characterized using SEM to evaluate the morphology, showing uniform dispersion of Ni nanoparticles with mean diameter of 12 to 20 nm. The modified carbon paste electrode was then used in methanol electrocatalytic oxidation reaction. Methanol oxidation on the proposed modified electrode surface occurs at 0.6 V and 0.3 V in alkaline and acidic medium respectively. Also, the results showed the better performance of modified electrode toward methanol electrocatalytic oxidation in comparison with carbon paste electrode that is modified by ion exchanged MMT. Charge transfer coefficients and apparent charge transfer rate constant for the modified electrode in the absence of methanol in alkaline medium were respectively found as: α_a = 0.53, α_c = 0.37 and k_s = 1.6 × 10⁻¹ s⁻¹. Also, the average value of catalytic rate constant for the electrocatalytic oxidation of methanol by the prepared nano-catalyst was estimated to be about 0.9 L·mol^-1·s^-1 by chronoamperometry technique. The prepared electrode was also effective for electrocatalytic oxidation of ethanol and formaldehyde in alkaline medium.     

Study of the effect of the concentration,size and surface chemistry of zirconia and silica nanoparticle fillers within an epoxy resin on the bulk properties of the resulting nanocomposites

Epoxy resin nanocomposites were prepared by curing bisphenol‐F with an aliphatic amine in the presence of SiO₂ and ZrO₂ nanoparticles as inorganic fillers. Both types of particles were prepared with diameters of around 10 nm and 70 nm to study size effects in the nanocomposites. The nanoparticles showed a different constitution: while silica was amorphous and spherical in nature, zirconia was crystalline and non‐spherical. Both nanoparticles were surface‐functionalized with novel diethylene‐glycol‐based capping agents to increase the compatibility with the epoxy matrix. The organic functionalities were attached to the nanoparticle surface via phosphonic acid (zirconia) and trialkoxysilane (silica) anchor groups. The homogeneity of the distribution of surface‐modified inorganic nano‐sized fillers in the matrix up to 5.8 vol% in case of silica and 2.34 vol% in case of zirconia was determined by small‐angle X‐ray scattering and transmission electron microscopy. Mechanical properties such as hardness and storage modulus were increased with increasing filler content while thermal stability of the obtained materials was nearly unaffected after incorporation of nanoparticles. Copyright © 2011 Society of Chemical Industry     

Effect of surface properties of polysulfone support on the performance of thin film composite polyamide reverse osmosis membranes

In this work, influence of initial conditions and surface characteristics of porous support layer on structure and performance of a thin film composite (TFC) polyamide reverse osmosis (RO) membrane was investigated. The phase inversion method was used for casting of polysulfone (PSf) supports and interfacial polymerization was used for coating of polyamide layer over the substrates. The effect of PSf concentrations that varied between 16 wt % and 21 wt %, and kind of the solvent (DMF and NMP) used for preparation of initial casting solution were investigated on the properties of the final RO membranes. SEM imaging, surface porosity, mean pore radius, and pure water flux analysis were applied for characterization of the supports. The substrate of the membrane, which synthesized with 18 wt % of PSf showed the most porosity and the synthesized RO membrane had the lowest salt rejection. In case of the solvents, the membranes synthesized with DMF presented better separation performance that can be attributed to their lower thickness and sponge‐like structure. The best composition of support for TFC RO membranes reached 16 wt % PSf in DMF solvent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44444.     

Fabrication and characterizations of crosslinked porous polymer films with varying chemical compositions

In this paper, we demonstrated the successful fabrication of crosslinked porous films with varying monomer-crosslinker ratios, by photo-induced crosslinking during the breath figure formation. For all the samples fabricated, the pores at the peripheral regions appeared more uniform in size and showed higher degree of ordering, due to the interplay between the solvent evaporation and crosslinking reaction. The pore morphology remains similar despite varying film compositions, suggesting that the pore-fixing process is still dominated by the solvent evaporation similar to that of conventional breath figure process, and is less dependent on the crosslinking process. Detailed characterizations of the chemical and physical properties, including the glass transition temperature, thermal stability, and surface wettability of the porous films were carried out.     

Synthesis and characterization of polyethylene glycol mediated silver nanoparticles by the green method

The roles of green chemistry in nanotechnology and nanoscience fields are very significant in the synthesis of diverse nanomaterials. Herein, we report a green chemistry method for synthesized colloidal silver nanoparticles (Ag NPs) in polymeric media. The colloidal Ag NPs were synthesized in an aqueous solution using silver nitrate, polyethylene glycol (PEG), and β-D-glucose as a silver precursor, stabilizer, and reducing agent, respectively. The properties of synthesized colloidal Ag NPs were studied at different reaction times. The ultraviolet-visible spectra were in excellent agreement with the obtained nanostructure studies performed by transmission electron microscopy (TEM) and their size distributions. The Ag NPs were characterized by utilizing X-ray diffraction (XRD), zeta potential measurements and Fourier transform infrared (FT-IR). The use of green chemistry reagents, such as glucose, provides green and economic features to this work.     

Identification and Field Evaluation of the Sex Pheromone of <Emphasis Type="Italic">Orthaga achatina</Emphasis> (Lepidoptera: Pyralidae)

Orthaga achatina (Lepidoptera: Pyralidae) is the most serious pest in south China of camphor trees, Cinnamomum camphora (L.) Presl, an important urban tree species. Gas chromatography-electroantennographic detection (GC-EAD) of the sex pheromone of O. achatina showed three EAD-active components. Coupled gas chromatography/mass spectrometry analyses identified these as (Z)-11-hexadecenol (Z11–16:OH), (Z)-11-hexadecenyl acetate (Z11–16:OAc), and (3Z,6Z,9Z,12Z,15Z)-tricosapentaene (Z3,Z6,Z9,Z12,Z15–23:H). In field tests using different combinations of the three compounds, male moths were attracted to a mixture of Z11–16:OAc and Z3,Z6,Z9,Z12,Z15–23:H, but less attracted to other blends. Further field tests with different ratios of the two compounds determined the optimal ratio of the binary blend as 500:250. The addition of Z11–16:OH to Z11–16:OAc, or to the binary mixture of Z11–16: OAc and the pentaene did not yield higher catches. This shows that O. achatina uses a mixture of Type I and Type II sex pheromone components. Orthaga achatina is the third Pyraloidea species found to utilize Z3,Z6,Z9,Z12,Z15–23:H as a sex pheromone component.     

Effects of Welding and rotational speeds on the Microstructure and Hardness of Friction Stir Welded Single-Phase Brass

This study focuses on the effects of rotational and welding speeds on the microstructure and hardness of joints in friction stir welded single-phase brass. Welds were achieved under low heat input conditions at rotational and welding speeds of 400-800 r/min and 100-300 mm/min, respectively. In order to characterize the obtained welds, optical microscopy and Vickers hardness measurements were taken on the weld cross sections. According to the obtained results, increasing the welding speed and/or decreasing the rotational speed caused the grain size of the stir zone to decrease and, hence, improved the average hardness of this region. These results are discussed with respect to the interplay between the welding parameters and the peak temperature in the weld thermal cycle.     

Using ARB process as a solution for dilemma of Si and SiCp distribution in cast Al-Si/SiCp composites

A major challenge in achieving the best potential of SiC_p-reinforced aluminum composites is to homogeneously disperse SiC particles within the aluminum alloys. The presence of coarse Si fibers with non-uniform distribution in cast Al-Si alloys, which may lead to poor mechanical properties, is another important problem that limits the application of these alloys. In order to eliminate these problems, accumulative roll bonding (ARB) process was used in this study as a very effective method for improving the microstructure and mechanical properties of the Al356/SiC_p composite. It was found that when the number of ARB cycles was increased, the uniformity of the Si and SiC_p in the aluminum matrix improved, the Si particles became finer and more spheroidal, the free zones of Si and SiC particles disappeared, the porosity of composite decreased, the bonding quality between SiC_p and matrix improved, and therefore mechanical properties of the composites were improved. The microstructure of the manufactured Al356/SiC_p composite after six ARB cycles indicated a completely modified structure so that its tensile strength and elongation values reached 318 MPa and 5.9%, which were 3.1 and 3.7 times greater than those of the as-cast composite, respectively.     

BSS: block-based sharing scheme for secure data storage services in mobile cloud environment

For the last few years, academia and research organizations are continuously investigating and resolving the security and privacy issues of mobile cloud computing environment. The additional consideration in designing security services for mobile cloud computing environment should be the resource-constrained mobile devices. The execution of computationally intensive security services on mobile device consumes battery’s charging quickly. In this regard, the study presents a novel energy-efficient block-based sharing scheme that provides confidentiality and integrity services for mobile users in the cloud environment. The block-based sharing scheme is compared with the existing schemes on the basis of energy consumption, CPU utilization, memory utilization, encryption time, decryption time, and turnaround time. The experimental results show that the block-based sharing scheme consumes less energy, reduces the resources utilization, improves response time, and provides better security services to the mobile users in the presence of fully untrusted cloud server(s) as compared to the existing security schemes.