Hamed Maleki

Structure of bottle-brush brushes under good solvent conditions: a molecular dynamics study.

We report a simulation study for bottle-brush polymers grafted on a rigid backbone. Using a standard coarse-grained bead-spring model extensive molecular dynamics simulations for such macromolecules under good solvent conditions are performed. We consider a broad range of parameters and present numerical results for the monomer density profile, density of the untethered ends of the grafted flexible backbones and the correlation function describing the range that neighboring grafted bottle-brushes are affected by the presence of the others due to the excluded-volume interactions. The end beads of the flexible backbones of the grafted bottle-brushes do not access the region close to the rigid backbone due to the presence of the side chains of the grafted bottle-brush polymers, which stretch the chains further in the radial directions. Although a number of different correlation lengths exist as a result of the complex structure of these macromolecules, their properties can be tuned with high accuracy in good solvents. Moreover, qualitative differences with typical bottle-brushes are discussed. Our results provide a first approach to characterizing such complex macromolecules with a standard bead-spring model.

Photocatalytic activity, optical and ferroelectric properties of Bi0.8Nd0.2FeO3 nanoparticles synthesized by sol-gel and hydrothermal methods

Abstract In this study, the effects of synthesis method and dopant neodymium ion on the ferroelectric properties and photocatalytic activity of bismuth ferrite were studied. BiFeO3 (BFO) and Bi0.8Nd0.2FeO3 (BNFO) nanoparticles were prepared through a facile sol-gel combustion (SG) and hydrothermal (HT) methods. The as-prepared products were characterized by X-ray powder diffraction (XRD), Furrier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM) images. Both nanophotocatalysts have similar crystal structures, but the SG products have semi-spherical morphology. On the other hand, HT samples have rod-like morphology. The ferroelectric properties of BNFO nanoparticles were improved compared to the undoped bismuth ferrite. The photocatalytic activity of as-synthesized nanoparticles was also evaluated by the degradation of methyl orange (MO) under visible light irradiation. The SG as-prepared nanoparticles exhibited a higher photocatalytic activity compared to powders obtained by HT method. Also substitution of Nd into the BFO structure increased the photocatalytic activity of bismuth ferrite.

The effect of calcination conditions on structural and magnetic behavior of bismuth ferrite synthesized by co-precipitation method

In this paper the effect of calcination conditions on structural properties, particle size, as well as the presence of secondary phases and magnetic characteristics of BiFeO3 nanocrystals have been investigated. Bismuth ferrite nanocrystals were synthesized at room temperature by chemical co-precipitation method. Phase analysis, structural and magnetic features and size of the produced nanopowders were studied via X-ray diffraction (XRD), Fourier transform infrared spectroscopy, transmission electron microscopy and vibrating sample magnetometer. The formation of the single phase compounds were confirmed by XRD. By analyzing the results from different measurements it was shown that products have the perovskite phase with space group R3C and the average nanocrystal size around 50xa0nm. The structural studies showed that calcination temperature and duration has crucial roles in disappearing impurities and secondary phases. Magnetic results in an applied field at room temperature indicated that the nanoparticles of bismuth ferrite have weak ferromagnetic order.

Janssen effect and the stability of quasi-two-dimensional sandpiles

We present the results of three-dimensional discrete element simulations of global normal stresses in quasi-two-dimensional sandpiles formed by pouring monodispersed cohesionless spherical grains into a vertical granular Hele-Shaw cell. We observe the Janssen effect which is the phenomenon of pressure saturation at the bottom of the container. Simulation of cells with different thicknesses shows that the Janssen coefficient κ is a function of the cell thickness. Dependence of global normal stresses as well as κ on the friction coefficients between the grains (μ(p)) and with walls (μ(w)) are also studied. The results show that in the range of our simulations κ usually increases with the wall-grain friction coefficient. Meanwhile by increasing μ(p) while the other system parameters are fixed, we witness a gradual increase in κ to a parameter dependent maximal value.

The angle of repose of spherical grains in granular Hele?Shaw cells: a molecular dynamics study

We report the results of three-dimensional molecular dynamic simulations on the angle of repose of a sandpile formed by pouring mono-sized cohesionless spherical grains into a granular Hele–Shaw cell. In particular, we are interested in investigating the effects of those variables which may have a significant impact on the pattern formation of granular mixtures in Hele–Shaw cells. The results indicate that the frictional forces influence the formation of piles on the grain level remarkably. Furthermore, we see that increasing grain insertion rate decreases the angle of repose slightly. We also find that the cell thickness is a significant factor and the angle of repose decays when the size of the gap between the lateral walls increases. In addition to agreeing with the experimental exponential decay law, our results are in accordance with a recently proposed model which takes into account the arching effects. Using grains with different sizes reveals that the behaviour of the angle of repose when both size and cell thickness are varied is controlled by a scaled function of the ratio of these two variables.

Synthesis and study of structural, optical and magnetic properties of BiFeO 3 –ZnFe 2 O 4 nanocomposites

In this work, structural, optical and magnetic properties of (1u2009−xu2009)BiFeO3–xZnFe2O4 (BFO–ZFO, xu2009=u20090, 0.2, 0.4, 0.6, 0.8 and 1) nanocomposite prepared by sol–gel method were studied. X-ray diffraction (XRD) analysis and Furrier transform infrared spectroscopy were investigated to determine the phase analysis and structural properties. XRD patterns indicated the presence of both BFO and ZFO crystalline phases. The averaged grain size and micro-strain was also determined using Scherrer formula and Williamson–Hall analysis. The agglomerated nature of the particles with continuous grain growth in all directions were found by the analysis of scanning electron microscope micrographs. UV–vis diffuse reflectance spectroscopy spectra showed that the optical band-gap was decreased by increasing zinc ferrite content. Magnetic properties of the samples were examined by vibrating sample magnetometer. The magnetic phase transition from ferromagnetic to paramagnetic order was observed by increasing Zn ferrite content.

Photocatalytic activity and magnetic enhancements by addition of lanthanum into the BiFeO 3 structure and the effect of synthesis method

In this paper, the photocatalytic activity, as well as the magnetic enhancement of multiferroics BiFeO3 (BFO) and Bi0.8La0.2FeO3 (BLFO) nanocrystals with two different morphologies, synthesized by two different sol–gel and hydrothermal (HT) methods, have been studied. All the obtained samples were characterized using X-ray diffractometer, Fourier transform infrared spectroscopy, transmission electron microscopy, UV–Vis spectroscopy and vibrating sample magnetometer. Differential thermal analysis measurements were probed ferroelectric- paraelectric first-order phase transition (TC) for all samples. Addition of lanthanum decreases the electric phase transition. For photocatalyst application of bismuth ferrite, adsorption potential of nanoparticles for methylene blue (MB) organic dye was evaluated. The doping of La in the BFO structure enhanced the photocatalytic activity and about 71% degradation of MB dye was obtained under visible irradiation. The magnetic properties of BLFO nanoparticles improve compared to the undoped BiFeO3 nanoparticles. The non-saturation at high applied magnetic field for as-prepared samples by HT is related to the size and shape of products. This work not only presents an effect of 20xa0mol% lanthanum substitution into the bismuth ferrite structure on the physical properties of BFO, but also compares the synthesis method and its influence on the photocatalytic activity and multiferroics properties of all nanopowders.