Synthesis of copper chloride and cobalt chloride doped polyanilines and their magnetic and alternating‐current transport properties

Polyaniline (PANI) was synthesized by the well‐known oxidative polymerization of aniline with ammonium peroxodisulfate as the oxidant. The morphological, structural, thermal, optical, magnetic, and electrical properties were characterized with scanning electron microscopy, X‐ray diffraction, Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry, ultraviolet–visible spectroscopy, room‐temperature magnetic measurements, and low‐temperature electrical transport measurements by the standard four‐probe method. Greater thermal stability and crystallinity were observed in doped PANI versus pure PANI. Magnetic measurements showed that the magnetic susceptibility was field‐dependent. Positive and negative susceptibility values were observed. This may have been due to the interactions of magnetic ions among interchains or intrachains of the polymer matrix. The alternating‐current (ac) conductivity was measured in the temperature range of 77–300 K in the frequency range of 20 Hz to 1 MHz. The frequency‐dependent real part of the complex ac conductivity was found to follow the universal dielectric response: σ′(f) ∝ f^s [where σ′(f) is the frequency‐dependent total conductivity, f is the frequency, and s is the frequency exponent] The trend in the variation of the frequency exponent with temperature corroborated the fact that correlated barrier hopping was the dominant charge‐transport mechanism for PANI–CoCl₂. An anomalous dependence on temperature of the frequency exponent was observed for PANI–CuCl₂. This anomalous behavior could not be explained in terms of existing theories. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A simple analysis of the Einstein relation in quantum confined non-parabolic semiconductors in the presence of a parallel magnetic field

An attempt is made to study the Einstein relation for the diffusivity-mobility ratio of the carriers in quantum confined non-parabolic semiconductors in the presence of a parallel magnetic field at low temperatures on the basis of new electron dispersion laws of quantum wells (QWs) and quantum wells wires (QWWs) of such materials. It is found, taking QW and QWWs of Hg_1–xCd_xTe and In_1–xGa_xAs_yP_1–y lattice-matched to InP as examples, that the diffusivity-mobility ratio increases with increasing electron concentration, decreasing alloy composition and decreasing film thickness in various oscillatory manners in both the cases. The magnetic field and the quantum wire structure enhance the numerical values of the same ratio. We have suggested an experimental method of determining the Einstein relation in degenerate materials having arbitrary dispersion laws. In addition, the corresponding well-known results of relatively wide-gap quantum confined materials in the absence of the magnetic field have been obtained as special cases of our generalized formulations, under certain limiting conditions.     

On the diffusivity-mobility ratio in ultrathin films of bismuth in the presence of crossed electric and magnetic fields

The Einstein relation is studied for the diffusivity-mobility ratio of the carriers in ultrathin films of bismuth in the presence of crossed electric and magnetic fields at very low temperatures, and the numerical results are presented for McClure and Choi, hybrid, Cohen, Lax, and ellipsoidal parabolic energy bands by formulating the respective modified carrier energy spectra. It is found that this ratio increases with decreasing film thickness, increasing electron concentration, and decreasing magnetic field. The quantum oscillations of the ratio show up much more significantly in the McClure than in the other models.     

A multi‐stub loaded compact UWB BPF with a broad notch band and extended stopband characteristics

A compact ultrawideband (UWB) bandpass filter (BPF) employing the principle of multiple mode resonance characteristics to create UWB passband with high selectivity and simultaneously having extensive stopband characteristic is presented. Utilizing five stubs attached along with the asymmetric trisection stepped impedance resonator (ATSSIR), the proposed resonator enables seven transmission poles inside the passband. As an additional attributes the projected filter triggers one transmission zero at 5.0 GHz which helps to mitigate WLAN signal interference. No additional circuitry is used to generate a notch band. The proposed prototype of UWB BPF is fabricated and estimated. Simulated and estimated results are in great understanding. The prospective filter displays a deliberate passband from 2.9 to 11.02 GHz. The filter unveils deceptive free wide upper stop band attributes till 25 GHz with least attenuation of 10 dB all through the stop band.     

Multi-helical micro-channels for rapid generation of drops of water in oil

High throughput generation of microscopic mono-dispersed droplets of one liquid into the continuous flow of another is important for large number of engineering and biomedical applications. However, meeting conflicting demands of both uniformity of size and high rate of droplet generation have been a difficult task to be accomplished in conventional systems. We have attempted to address this problem by designing a novel multi-helical micro-channel which we have used to generate water droplets in a continuous flow of oil. The channel consists of three or more helical flow paths joined along their contour length forming a single channel with inherently asymmetric geometry. Helix angle and radius are found to be two additional geometric parameters which influence different drop break-up regimes. We have shown that both time period of generation of drops and the droplet size can be minimized by suitably altering the helix angle. A scaling law has been derived to rationalize these results.     

Sintering characteristics of in situ formed low expansion ceramics from a powder precursor in the form of hydroxy hydrogel

Lithium aluminosilicate powder precursors of compositions Li₂O:Al₂O₃:SiO₂ as 1:1:2; 1:1:2.5 and 1:1:3 were prepared in the hydroxy hydrogel form by wet interaction technique in aqueous medium followed by sintering for ultimate synthesis of low expansion ceramics. Phases formed in the sintered specimens were analyzed by XRD technique. Thermal expansion of the specimens sintered at 1100, 1200 and 1300 °C were also measured. It was found that β-spodumene, lithium aluminum oxide and silica were the predominat phases in all the specimens. Sintering was optimum up to 1200 °C beyond which no further noticeable shrinkage was observed. The sintered specimens remained highly porous even after firing at 1300 °C, whose bulk density and apparent porosity were in the range of 1.25–1.42 g/cm³ and 43–48%, respectively. Thermal expansion characteristics and density of the sintered specimens were found to be primarily related to the composition of the phases formed during sintering. A porous low expansion ceramic monolith could be prepared using the present technique.     

Fibrillar Elastomeric Micropatterns Create Tunable Adhesion Even to Rough Surfaces

Biologically inspired, fibrillar dry adhesives continue to attract much attention as they are instrumental for emerging applications and technologies. To date, the adhesion of micropatterned gecko‐inspired surfaces has predominantly been tested on stiff, smooth substrates. However, all natural and almost all artificial surfaces have roughnesses on one or more different length scales. In the present approach, micropillar‐patterned PDMS surfaces with superior adhesion to glass substrates with different roughnesses are designed and analyzed. The results reveal for the first time adhesive and nonadhesive states depending on the micropillar geometry relative to the surface roughness profile. The data obtained further demonstrate that, in the adhesive regime, fibrillar gecko‐inspired adhesive structures can be used with advantage on rough surfaces; this finding may open up new applications in the fields of robotics, biomedicine, and space exploration.     

Green synthesis of highly stabilized nanocrystalline silver particles by a non-pathogenic and agriculturally important fungus T. asperellum

A controlled and up-scalable biosynthetic route to nanocrystalline silver particles with well-defined morphology using cell-free aqueous filtrate of a non-pathogenic and commercially viable biocontrol agent Trichoderma asperellum is being reported for the first time. A transparent solution of the cell-free filtrate of Trichoderma asperellum containing 1?mM AgNO(3) turns progressively dark brown within 5?d of incubation at 25?°C. The kinetics of the reaction was studied using UV-vis spectroscopy. An intense surface plasmon resonance band at ～410?nm in the UV-vis spectrum clearly reveals the formation of silver nanoparticles. The size of the silver particles using TEM and XRD studies is found to be in the range 13-18?nm. These nanoparticles are found to be highly stable and even after prolonged storage for over 6 months they do not show significant aggregation. A plausible mechanism behind the formation of silver nanoparticles and their stabilization via capping has been investigated using FTIR and surface-enhanced resonance Raman spectroscopy.     

Polypropylene-clay composite prepared from Indian bentonite

In the present work, a set of experimental polypropylene (PP) clay composites containing pristine bentonite clay of Indian origin has been prepared and then characterized. The polymer clay composites are processed by solution mixing of polypropylene with bentonite clay using a solvent xylene and high speed electric stirrer at a temperature around 130°C and then by compression molding at 170°C. The mechanical properties of PP-clay composites like tensile strength, hardness and impact resistance have been investigated. Microstructural studies were carried out using scanning electron microscope and transmission electron microscope and the thermal properties were studied using differential scanning calorimeter. Mechanical properties of the prepared composites showed highest reinforcing and toughening effects of the clay filler at a loading of only 5 mass % in PP matrix. Tensile strength was observed to be highest in case of 5 mass % of clay loading and it was more than 14% of that of the neat PP, while toughness increased by more than 80%. Bentonite clay-PP composite (5 mass %) also showed 60% increase in impact energy value. However, no significant change was observed in case of hardness and tensile modulus. Higher percentages of bentonite clay did not further improve the properties with respect to pristine polypropylene. The study of the microstructure of the prepared polymer layered silicate clay composites showed a mixed morphology with multiple stacks of clay layers and tactoids of different thicknesses.     

Magnetic Field and Displacement Sensor Based on Giant Magneto-Impedance Effect

A two-core transducer assembly using a Fe_73.5Nb₃Cu₁Si_13.5B₉ ribbon to detect a change of magnetic field is proposed and tested for displacement (linear and angular) and current sensor. Two identical inductors, with the ribbon as core, are part of a two-series resonance network, and are in a high impedance state when excited by a small AC field of 1 MHz in the absence of a DC biasing field (H_dc). When the magnetic state of one inductor is altered by the biasing field, produced by a bar magnet or current carrying coil, an AC signal proportional to H_dc is generated by the transducer. The results for the sensitivity and linearity with displacement (linear and angular) of a magnet and with field from the current carrying coil are presented for two particular configurations of the transducer. High sensitivities of voltage response as much as 12 µV/µm and 3 mV/degree have been obtained for the transducer as a linear and angular displacement sensor, respectively, in the transverse configuration of exciting AC and biasing DC fields.