Studies on thermodynamic compatibility of nitrile rubber and polybutadiene by inverse gas chromatography

Inverse gas chromatography technique has been used to study the thermodynamic compatibility of the industrially important elastomers polybutadiene (BR) and polybutadiene copolymerised with acrylonitrile (NBR). The NBR used in this study had nitrile contents of 18 and 34%. The ratio of BR/NBR in blends varied between 1 and 0.25 in both cases and retention volume of twelve probes was measured at 80°C. The Flory-Huggins interaction parameter X′₂₃, computed using a standard procedure, and also the interaction parameter B₂₃ showed that BR and NBR are incompatible in all compositions and that incompatibility increases with nitrile content. © 1995 John Wiley & Sons, Inc.     

Influence of carbon nanotube dispersion on the mechanical properties of phenolic resin composites

Despite the much touted mechanical properties of carbon nanotubes, composites reinforced with nanotubes have failed to achieve mechanical properties which rival those present in conventional fiber reinforced polymer composites. This article describes an attempt to bridge this gap. Multi‐walled carbon nanotubes (MWCNT) were synthesized using a chemical vapor deposition method and were dispersed in phenolic resin by both the wet and dry dispersion techniques before molding into composite bars (50 × 5 × 3 mm³). Although no improvement in the mechanical properties of the MWCNT/phenolic composites was observed over the neat resin value when wet mixing dispersion was employed, an improvement of nearly 158% (160 MPa as compared with 62 MPa for neat resin) was achieved in 5 vol% MWCNT containing phenolic resin prepared by the dry mixing. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Nanoscale structure and atomic disorder in the iron-based chalcogenides

The multiband iron-based superconductors have layered structure with a phase diagram characterized by a complex interplay of charge, spin and lattice excitations, with nanoscale atomic structure playing a key role in their fundamental electronic properties. In this paper, we briefly review nanoscale structure and atomic disorder in iron-based chalcogenide superconductors. We focus on the Fe(Se,S)_1−xTe_x (11-type) and K_0.8Fe_1.6Se₂ (122-type) systems, discussing their local structure obtained by extended x-ray absorption fine structure. Local structure studies on the Fe(Se,S)_1−xTe_x system reveal clear nanoscale phase separation characterized by coexisting components of different atomic configurations, similar to the case of random alloys. In fact, the Fe–Se/S and Fe–Te distances in the ternary Fe(Se,S)_1−xTe_x are found to be closer to the respective distances in the binary FeSe/FeS and FeTe systems, showing significant divergence of the local structure from the average one. The observed features are characteristic of ternary random alloys, indicating breaking of the local symmetry in these materials. On the other hand, K_0.8Fe_1.6Se₂ is known for phase separation in an iron-vacancy ordered phase and an in-plane compressed lattice phase. The local structure of these 122-type chalcogenides shows that this system is characterized by a large local disorder. Indeed, the experiments suggest a nanoscale glassy phase in K_0.8Fe_1.6Se₂, with the superconductivity being similar to the granular materials. While the 11-type structure has no spacer layer, the 122-type structure contains intercalated atoms unlike the 1111-type REFeAsO (RE = rare earth) oxypnictides, having well-defined REO spacer layers. It is clear that the interlayer atomic correlations in these iron-based superconducting structures play an important role in structural stability as well as superconductivity and magnetism.     

Characterization and identification of essential residues of the glycoside hydrolase family 64 laminaripentaose-producing-β-1, 3-glucanase

Laminaripentaose-producing β-1,3-glucanase (LPHase) from Streptomyces matensis DIC-108 uniquely catalyzes the hydrolysis of β-1,3-glucan to release laminaripentaose as the predominant product. For studying this novel enzyme, the gene of LPHase was reconstructed with polymerase chain reaction and over-expressed in Escherichia coli. The recombinant wild-type enzyme and various mutants were further purified to >90% homogeneity on an ion-exchange chromatograph. The catalysis of the recombinant LPHase is confirmed to follow a one-step single-displacement mechanism with (1)H-NMR spectrometry. To determine the amino-acid residues essential for the catalysis, more than ten residues, including five highly conserved residues--Asp(143), Glu(154), Asp(170), Asp(376) and Asp(377), were mutated. Among the mutants, E154Q, E154G, D174N and D174G significantly lost catalytic activity. Further investigation with chemical rescue using sodium azide on E154G and D174G confirmed that Glu(154) functions as the general acid whereas Asp(170) serves as the general base in a catalytic turnover. This work is the first report that provides direct information for the identification of the essential residues of GH-64 through kinetic examination.     

A low-power biologically-inspired chaotic oscillator with process and temperature tolerance

This paper presents a low-power, biologically-inspired silicon neuron based implementation of a chaotic oscillator circuit. The silicon neuron structure is based on Hodgkin–Huxley neuron model. Subthreshold MOSFET and current reuse techniques have been utilized to achieve a low-power consumption of 180.30 nW for the room temperature (27 °C) and typical process corner. The chaotic behavior of the circuit is confirmed by calculating the largest Lyapunov exponent. A sensitivity analysis of the proposed chaotic oscillator shows that the circuit maintains the chaotic behavior for five different process corners within the temperature range of 0–60 °C.     

Synthesis of Nanocrystalline Lanthanum Strontium Manganite Powder by the Urea–Formaldehyde Polymer Gel Combustion Route

Nanocrystalline lanthanum strontium manganite (LSM) powder has been synthesized by combustion of a transparent gel obtained by the polymerization of methylol urea and urea in a solution containing La³⁺, Sr²⁺, and Mn²⁺ (LSM ions). Chemistry of the transparent urea–formaldehyde (UF) polymer gel formation and structure of the gel have been proposed such that the LSM ions act in between the growing UF polymer chains by interacting through NH, OH, and CO groups by co-ordination and prevent polymer self-assembly through inter-chain hydrogen bonding as evidenced from infrared spectrum. Thermally stable structures formed by the decomposition of UF polymer below 300°C undergo combustion in the presence of nitrate oxidant in a temperature range from 350°–450°C. A perovskite LSM phase has been formed by self-sustained combustion of the dried gel initiated with little kerosene. The powder obtained after deagglomeration and calcination at 600°C for 2 h has a D ₅₀ value of 0.19 μm, and the particles are aggregates of crystallites 10–25 nm in size.     

Tribo-investigation on PTFE lubricated PEEK in harsh operating conditions

A series of blends with Polytetrafluroethylene (PTFE) powder and Polyetheretherketone (PEEK) was developed by varying the PTFE contents in steps of 5 wt.% from 0 to 20 wt.%. The composites were evaluated for their friction and wear properties at room temperature as well as high temperature in low amplitude oscillating wear (LAOW) mode against steel (100 Cr 6) ball against polymer plate. The same blends were also evaluated in abrasive wear mode to study the influence of harsh operating conditions on wear and friction performance. Incorporation of PTFE benefited PEEK in various ways such as it increased the tribo-utility of the latter by increasing its limiting load value, removing its stick-slip tendency, lowering coefficient of friction and specific wear rate significantly. With increase in PTFE content, benefits to the wear performance increased regularly. This was not the case for friction coefficient. Lowest μ was recorded for 15% PTFE contents. The enhancement in wear and friction performance, however, was at the cost of strength properties which decreased substantially with increase in PTFE content. At 100 °C, friction coefficient and wear rates of all blends increased marginally. In abrasive wear mode, on the other hand, PTFE filled PEEK showed poorer wear resistance than neat PEEK. This was correlated with strength properties and it was observed that these blends closely followed the predictions of Ratner–Lancaster plot. SEM was used to examine the micro-structural features of worn surfaces.