Modification of Theoretical models to predict mechanical behavior of PVC/NBR/organoclay nanocomposites

Organo‐modified nanoclay (Cloisite 30B) was added via direct melt mixing to the acrylonitrile butadiene rubber/poly(vinyl chloride) (PVC/NBR) to fabricate polymer blend/clay nanocomposites. The states of nano‐fillers dispersion were investigated by transmission electron microscopy (TEM) and X‐ray diffraction (XRD). From the morphological study of nanocomposites, it is concluded that exfoliated morphology is obtainable by introduction of 2.5 vol % of nanoclay. The effect of nano‐filler volume content on the mechanical properties of PVC/NBR matrix reinforced by Cloisite 30B was investigated by tensile test. Experimental results show that the Young's modulus and tensile strength of composites can significantly improved with a small amount of nanofiller. Moreover, to investigate the stress–strain behavior of NBR/PVC nanocomposites, seven constitutive models such as Arruda–Boyce, Mooney–Rivilen, Marlow, second order of polynomial, Van der Waals, and third order Odgen were studied and compared with experimental data. Results showed that Malow and second order polynomial model can be used for nanoclay‐filled compound whereas the other models show more deviation from experimental data. Three micromechanical models named liner rule of mixtures (LROM) and the inverse rule of mixtures (IROM). Halpin–Tsai theory was applied to evaluate the dependence of Young modulus of nanocomposites on volume fraction of nanofiller. Two modifying factors were proposed to evaluate the Young's modulus of nanocomposites which could greatly improve the theoretical prediction obtained from inverse rule of mixtures (IROM) and Halpin–Tsai equation. The modifying factors were introduced by adopting an exponential, power‐law and linear factors in the equation. In order to verify the suitability of the modified models, the ensuing theoretical predictions are compared to the other experimental data available in the literature. Good predictability of the modified models is demonstrated in the results. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3229–3239, 2013     

A comparative study on curing characteristics and thermomechanical properties of elastomeric nanocomposites: The effects of eggshell and calcium carbonate nanofillers

After‐hatching eggshell (AHES) nanobiofiller and nanocalcium carbonate (nano‐CA) were separately added to various elastomers, such as acrylonitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), and natural rubber (NR), in various amounts of 5, 10, and 15 phr. The effect of particle size and dispersion of such nanofillers on thermomechanical properties and curing characteristics were then investigated. The ultimate tensile properties of SBR and NR nanocomposites were improved to some extent when 5 phr of AHES nanofiller was added to the rubber compound compared to CA. In the case of NBR nanocompounds, however, the mechanical properties were seemingly comparable, irrespective of the type of nanofiller. This contradictive behavior could be attributed to the alteration of crosslink density due to particular filler–matrix interaction while using mineral and natural fillers. The results of the rheometric study revealed that using AHES rather than CA slightly increases the scorch time of all types of prepared nanocomposites, whereas a significant drop in the optimum curing time was seen for NBR nanocomposites containing AHES biofiller. Moreover, thermogravimetric analysis showed similar thermal stability for SBR nanocomposites containing AHES and CA fillers. Finer particle size of CA and higher porosity of AHES at high and low loading levels were respectively the main reasons for improvement of ultimate properties. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Interactive Effects of Simulated Nitrogen Deposition and Altered Precipitation Patterns on Plant Allelochemical Concentrations

Global environmental change alters the supply of multiple limiting resources that regulate plant primary and secondary metabolism. Through modifications in resource availability, acquisition, and allocation, global change is likely to influence plant chemical defenses, and consequently species interactions that are mediated by these compounds. While many studies focus on individual global change factors, simultaneous changes in abiotic factors may interact to influence plant allelochemicals. In this study, we examined the individual and interactive effects of nitrogen enrichment and altered precipitation patterns on chemical defense compounds (iridoid glycosides) of an invasive plant, Linaria dalmatica. Plants were grown from seed in native mixed-grass prairie for 2 years. Nitrogen and water treatments were applied in each growing season over this period. Results indicate that soil water and nitrogen availability interact to shape plant chemical defense concentrations in L. dalmatica. Nitrogen addition decreased iridoid glycoside concentrations by approximately 25 % under reduced water availability, increased concentrations by 37 % in ambient water plots, and had no effect on these chemical defenses for plants growing under augmented water supply. Thus, results show differing patterns of allelochemical response to nitrogen enrichment, with respect to both the magnitude and direction of change, depending on water availability. Our study demonstrates the importance of examining multiple environmental factors in order to predict potential changes in plant chemical defenses with climate change.     

Application of silica gel/polyaniline composite for adsorption of ascorbic acid from aqueous solutions

Silica gel and a chemically modified silica gel with polyaniline (PAN) were used for adsorption of ascorbic acid (AA) from aqueous solutions. The surface morphology of the adsorbents was studied by scanning electron microscopy (SEM). Adsorption experiments were carried out using both batch and columnar systems. In batch system, the effects of some important parameters such as sorbent dose, contact time, initial concentration and temperature of the adsorbate were studied. Based on regression analysis, the sorption data obtained for SiO₂ were best represented by Freundlich isotherm and for the PAN/SiO₂ composite, the equilibrium sorption data were fitted better by Langmuir isotherm. The kinetic studies showed that the adsorption of AA on both sorbents follows pseudo second-order kinetics which implies a chemisorption mechanism and according to diffusion model, intra-particle diffusion is the rate-controlling step. The thermodynamic studies also showed that PAN/SiO₂ is a more effective adsorbent to adsorb AA than an unmodified SiO₂. In columnar mode, the effects of salt on breakthrough curve were investigated. Two kinetic models, Thomas and Adams–Bohart, were applied to experimental data to predict the breakthrough curves using linear regression and determine the characteristic parameters of the column. Error analysis was carried out to investigate the adequacy and accuracy of the model equations. Desorption study showed that the adsorbed ascorbic acid is readily eluted from the column using dilute solution of NaOH. PAN/SiO₂ was found to be a promising solid phase adsorbent to preconcentrate ascorbic acid from aqueous solutions and subsequent analysis.     

Fusion level optimization of rigid PVC nanocompounds by using response surface methodology

The influence of the type and content of organically modified nanoclay (NC) and the amount of calcium stearate (Ca.St) on the fusion characteristics of a poly(vinyl chloride) (PVC) nanocomposite was studied by using response surface methodology. To interpret the fusion behavior, different PVC/NC compounds were prepared in a Plasticorder with a constant rotor speed of 60 rpm while keeping the processing time and temperature constant. The results revealed that introducing NC particles into the PVC compound resulted in an increase in the maximum torque (MAT), while the minimum torque (MIT) declined. On the contrary, both the MAT and MIT values slightly increased with increasing Ca.St content. It was also found that with increasing NC content, the fusion time increased and the fusion factor decreased, whereas increasing the Ca.St lowered the fusion time. Furthermore, the difference between the MIT and MAT values demonstrated multifarious behaviors depending on the material type. Ultimately, a correlation was established between the material characteristics and the fusion factor of the PVC nanocompounds. J. VINYL ADDIT. TECHNOL., 19:168‐176, 2013. © 2013 Society of Plastics Engineers     

Nanostructure silver-doped zinc oxide films coating on glass prepared by sol–gel and photochemical deposition process: Application for removal of mercaptan

Silver-doped zinc oxide (SDZO) films have been grown on glass substrate by a novel combination of sol–gel and photochemical deposition processes (SGPD). The effect of sintering on structural, electrical and optical properties was investigated. The films were characterized by UV–vis absorption spectroscopy (UV–vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The result of X-ray photoelectron spectroscopy (XPS) revealed that the binding energy of Ag 3d_5/2 for SDZO shifts remarkably to the lower binding energy compared to the pure metallic Ag due to the interaction between silver and zinc oxide. The XRD spectra of the SDZO films indicate that silver was incorporated in the hexagonal crystal structure of zinc oxide. SEM micrographs show the uniform distribution of spherical grains of about 73 nm grain size for the pure zinc oxide thin films. The results indicated that silver doping photochemical deposition was a feasible method to tune the optical properties of zinc oxide nanostructures. SDZO films coated on glass were applied for the photodegradation of mercaptan in water. SDZO films were applied for degradation of mercaptobenzoxazole which reduced the mercaptan concentration to more than 98%.     

Determination of Tehran Research Reactor power by N gamma detection

The radioisotope ¹⁶N is produced by the interaction of fast neutrons with ¹⁶O in water reactor coolant. This radioisotope emits at the two major gamma ray energies of 6.13 MeV and 7.1 MeV. Exploiting the linear relation between the number of gamma particles versus the reactor power change, the reactor power is determined by detecting and counting the emitted gammas. In this work, for the detection of gammas to measure the reactor power, two different methods are employed. First, by NaI(Tl) scintillator detector and second, by assembly of ten GM detectors. The obtained results confirm that the number of emitted gammas is proportional to the change in reactor power as shown by different monitoring systems such as UIC, CIC, FC, Cherenkov and thermal power. Both of the applied methods are shown to give reliable results for reactor power above 20 kW. Both systems, having been calibrated, are being used as monitoring systems of power in Tehran Research Reactor. These systems are usable in other research reactors and possibly in power reactors as well.     

Cognitive style may mitigate the impact of communication mode

With the proliferation of Internet-based applications for collaborative work such as group decision support system (GDSS), traditional face-to-face (FTF) interactions are being augmented or replaced by screen-to-face (STF) technology. Extant research results find that some individuals prefer FTF mode for interaction and would feel frustrated under an STF mode, but others may feel very comfortable using electronic STF applications. This paper evaluates the influence of cognitive style on the perception of individuals negotiating over FTF or STF communication modes. Cognitive style explains how individuals prefer to receive information and what methods they use to process that information. The results suggest that when individuals are faced with a mixed-motive negotiation task, some cognitive styles mitigate the effects of communication modes while other cognitive styles are not sensitive to it. Hence, cognitive style and communication modes have interaction effects.     

Synthesis,characterization, and supercapacitor studies of manganese (IV) oxide nanowires

One-dimensional manganese (IV) oxide (MnO₂) (～20 nm in average diameter) were synthesized by cathodic electrodeposition and heat treatment. The mechanism of electrodeposition and nanowire formation were discussed. The product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR). Nanowires with varying lengths and diameters were found in TEM and SEM images of the sample. The results of N₂ adsorption–desorption analysis indicated that the BET surface area of the MnO₂ nanowires was 157 m² g^?1 and the pore size distributions were 2.5 and 4.5 nm. The electrochemical performances of the prepared MnO₂ as an electrode material for supercapacitors were evaluated by cyclic voltammetry and galvanostatic charge/discharge measurements in a solution of 0.5 M Na₂SO₄. The higher specific capacitance of 318 F g^?1 and good capacity retention of 86% were achieved after 1000 charge–discharge cycles had been observed for the MnO₂ nanowires electrode.     

Top‐Down Fabrication of High Quality III–V Nanostructures by Monolayer Controlled Sculpting and Simultaneous Passivation

In the fabrication of III–V semiconductor nanostructures for electronic and optoelectronic devices, techniques that are capable of removing material with monolayer precision are as important as material growth to achieve best device performances. A robust chemical treatment is demonstrated using sulfur (S)‐oleylamine (OA) solution, which etches layer by layer in an inverse epitaxial fashion and simultaneously passivates the surface. The application of this process to push the limits of top‐down nanofabrication is demonstrated by the realization of InP‐based high optical quality nanowire arrays, with aspect ratios more than 50, and nanostructures with new topologies. The findings are relevant for other III–V semiconductors and have potential applications in III–V device technologies.