A comprehensive study on the kinetics of aqueous free-radical homo- and copolymerization of acrylamide and diallyldimethylammonium chloride by online 1H-NMR spectroscopy

Free-radical homo- and copolymerization of acrylamide (AAm) and diallyldimethylammonium chloride (DADMAC) initiated with potassium persulfate (KPS) were performed in the presence of 0.1 M NaCl solution in D₂O at 50 °C. Online ¹H-NMR kinetic experiments were used to study polymerization kinetics via determination of the individual and overall conversion of the comonomers and compositions of the comonomer mixture and produced copolymer as a function of the reaction time. Reactivity ratios of the AAm and DADMAC were calculated by Mao-Huglin (MH) and extended Kelen-Tudos (KT) methods to be 7.0855?±?1.3963, 0.1216?±?0.0301 and 6.9458?±?2.0113, 0.1201?±?0.0437 respectively. “Lumped” kinetic parameter (k _p k _t ^??0.5 ) was estimated from experimental data. Results showed that k _p k _t ^??0.5 value increases by increasing mole fraction of the AAm in the initial reaction mixture. Drift in the comonomer mixture and copolymer compositions with reaction progress was evaluated experimentally and theoretically. Theoretical values were calculated from Meyer-Lowry equation by using reactivity ratios obtained from MH method. A good fitting between the experimental and theoretical values was observed, indicating accuracy of the reactivity ratios estimated in the present work. It was found from following changes in the copolymer composition with the comonomer conversion that produced copolymer has a statistical structure.     

Morphology transition control of polyaniline from nanotubes to nanospheres in a soft template method

A soft template route is reported for the fabrication of polyaniline nanospheres via the oxidative polymerization of aniline in the presence of β‐naphthalenesulfonic acid (β‐NSA) as both surfactqant and dopant, and ammonium persulfate as oxidant at 2–5 °C. Control over the morphology and size of the nanoparticles was achieved by changing the reaction medium via addition of an organic cosolvent (i.e. ethanol or ethylene glycol) and by controlling the concentrations of aniline and β‐NSA and the molar ratio of β‐NSA to aniline. By this means the size of the β‐NSA–aniline micelles and the way that aniline monomer interacts with the micelles were controlled. In fact the lower dielectric constant of organic cosolvent, due to reduction of the possibility of dissociation of ionic species, causes the monomer to exist mostly as neutral aniline molecules rather than as anilinium cations. The neutral aniline molecules form aniline‐filled micelles with β‐NSA, which act as soft templates for the formation of polyaniline nanospheres. Scanning and transmission electron microscopies, dynamic light scattering, and Fourier transform infrared and UV‐visible spectroscopies were used to characterize the products. The mechanism of morphology transition from nanotubes to nanoparticles is discussed based on the experimental observations. © 2014 Society of Chemical Industry     

Novel design of a RF-MEMS tuneable capacitor based on electrostatically induced torsion

Micro-Electro-Mechanical System (MEMS) RF switches have been one of the most interesting areas for research and development in the last years. It has been shown that they have an excellent performance in the RF and microwave frequency range and a great effort has been dedicated in designing suitable geometries and structures best suited for switching application. In parallel other devices useful for the construction of complex RF circuits have been proposed and studied. Among these tuneable capacitors are of high interest for a variety of applications. In this paper we present a new electromechanical design for a tuneable capacitor with a totally different shape from usual designs. In particular we try to exploit the effect of the small in-plane force that develops during the polarization of a parallel plate capacitor with partially overlapping plates. First prototype realizations aiming at the development of the electromechanic aspects of the concept are discussed and analyzed and as the first realization showed some problems an improved design is presented.     

Silicon‐Based Anodes for Lithium‐Ion Batteries: From Fundamentals to Practical Applications

Silicon has been intensively studied as an anode material for lithium‐ion batteries (LIB) because of its exceptionally high specific capacity. However, silicon‐based anode materials usually suffer from large volume change during the charge and discharge process, leading to subsequent pulverization of silicon, loss of electric contact, and continuous side reactions. These transformations cause poor cycle life and hinder the wide commercialization of silicon for LIBs. The lithiation and delithiation behaviors, and the interphase reaction mechanisms, are progressively studied and understood. Various nanostructured silicon anodes are reported to exhibit both superior specific capacity and cycle life compared to commercial carbon‐based anodes. However, some practical issues with nanostructured silicon cannot be ignored, and must be addressed if it is to be widely used in commercial LIBs. This Review outlines major impactful work on silicon‐based anodes, and the most recent research directions in this field, specifically, the engineering of silicon architectures, the construction of silicon‐based composites, and other performance‐enhancement studies including electrolytes and binders. The burgeoning research efforts in the development of practical silicon electrodes, and full‐cell silicon‐based LIBs are specially stressed, which are key to the successful commercialization of silicon anodes, and large‐scale deployment of next‐generation high energy density LIBs.     

Environmental vulnerability assessment of Choghakhor International Wetland during 1985 to 2018

As of natural constraints, and the specific climate of Iran, as well as the increasing importance of international water resources in the socio‐economic development of societies, studies on surface water resources, especially wetlands, merit special attention. Accordingly, the TM, ETM+ and OLI satellite images of 1985, 2000 and 2018 were used in the present study to detect changes in the Choghakhor international wetland. Classifying the images with a supervised method, and using maximum likelihood algorithms, the distinct land use/land cover classes of waterbody, aquatic plants, pasture and forest, agricultural lands, bare land and human built lands were ranked. Selected landscape metrics information on the spatial pattern of the Choghakhor wetland was quantitatively determined, using Fragstats software, and the spatial composition and vulnerability of the wetland were evaluated. The vulnerability assessment of wetland contamination was investigated using the WRASTIC index based on the catchment area scale. Time processing of the data obtained from the maps indicated a 26.63% decrease in the pasture and forest area, and a 12.1% increase in the area of human built lands and agriculture lands during the period from 1985 to 2018. Further, in spite of the waterbody area expanding during 1985 to 2000, it subsequently shrunk in size from 2000 to 2018, with the area of aquatic plants lands increasing during the same period. Analysis of landscape metrics generally indicated the natural wetland cover has been changing during this period along with increasing anthropogenic impacts. Degradation, rotation and replacement of natural land cover such as pastures and forests with human built areas can be considered undesirable development effects on the Choghakhor wetland. The results of the WRASTIC index calculation indicated a major impact of Choghakhor wetland components from water pollution. The results of the present study place an emphasis on more sustainable land use and prevention of land destruction in the Choghakhor wetland basin.     

Cane molasses fermentation for continuous ethanol production in an immobilized cells reactor by Saccharomyces cerevisiae

Sodium-alginate immobilized yeast was employed to produce ethanol continuously using cane molasses as a carbon source in an immobilized cell reactor (ICR). The immobilization of Saccharomyces cerevisiae was performed by entrapment of the cell cultured media harvested at exponential growth phase (16 h) with 3% sodium alginate. During the initial stage of operation, the ICR was loaded with fresh beads of mean diameter of 5.01 mm. The ethanol production was affected by the concentration of the cane molasses (50, 100 and 150 g/l), dilution rates (0.064, 0.096, 0.144 and 0.192 h^?1) and hydraulic retention time (5.21, 6.94, 10.42 and 15.63 h) of the media. The pH of the feed medium was set at 4.5 and the fermentation was carried out at an ambient temperature. The maximum ethanol production, theoretical yield (Y_E/S), volumetric ethanol productivity (Q_P) and total sugar consumption was 19.15 g/l, 46.23%, 2.39 g l^?1 h^?1 and 96%, respectively.     

Silicon Nanoparticles and Methyl Jasmonate Improve Physiological Response and Increase Expression of Stress-related Genes in Strawberry cv. Paros Under Salinity Stress

Silicon - Salinity is one of the most crucial abiotic stresses, which is the consequence of an increase in the concentration of NaCl ions, influencing the plant’s growth, development, and...