Effect of polymer bridging on rheological properties of dispersions of charged silica particles in the presence of low-molecular-weight physically adsorbed poly(ethylene oxide)

 The effect of a low-molecular-weight physically adsorbed poly(ethylene oxide) on the rheological behavior of aqueous dispersions of silica particles (as a model system) has been investigated. Particular attention is given to the evolution of the rheological behavior with increasing polymer concentration in the system at different volume fractions of the particles. Experiments were performed in the absence of salt and just the pH of the dispersion was adjusted to 9.5, a condition at which the system is electrostatically stable and electrostatic repulsive forces are long range in nature. It was observed that the shear viscosity and the linear viscoelastic functions of the dispersion at 55 vol% increase initially through the addition of polymer, reach a maximum, and then decrease to a minimum with further addition of polymer to the system. At higher polymer concentrations, there may be an increase in the viscosity of the dispersion owing to an increase in the concentration of free polymer chains in the medium causing depletion flocculation in the system. The increase in the rheological behavior of the dispersion at low polymer coverage is attributed to polymer bridging flocculation caused by a low-molecular-weight poly(ethylene oxide) in the system. Comparison of the data given here with the results of earlier studies on the viscosity behavior of the system in the presence of salt (0.01 M) indicates that the range of the electrostatic repulsion has a significant role in the rheological behavior of the system. Received: 7 February 2001 Accepted: 18 October 2001     

Novel 5‐Acetyl‐3‐aryl‐2‐thioxo‐dihydropyrimidine‐4,6(1H,5H)‐diones: One Pot Three‐Component Synthesis,Characterization and Antibacterial Activity

A series of new 5‐substituted thiobarbituric acid derivatives 5‐acetyl‐3‐aryl‐2‐thioxo‐dihydropyrimidine‐4,6(1H,5H)‐diones ( 2a , 2b , 2c , 2d , 2e , 2f , 2g , 2h ) were synthesized by one pot cyclocondensation of 1‐aroyl‐3‐arylthioureas with malonic acid in the presence of acetic anhydride. These compounds exist in equilibrium with their enolic tautomeric forms 5‐(1‐hydroxy ethylidene)‐3‐aryl‐2‐thioxo‐dihydropyrimidine‐4,6‐(1H,5H)‐diones. The structures were confirmed by spectroscopic data, elemental analyses and in case of the 2d by single crystal X‐ray diffraction data. A plausible mechanism for the formation of products is also proposed. Compounds ( 2a , 2b , 2c , 2d , 2e , 2f , 2g , 2h ) were evaluated for their preliminary antibacterial activity against a representative panel of Gram positive and Gram negative bacteria using levofloxacin as the reference drug and were found to exhibit promising activity. The tested compounds displayed different levels of inhibitory effects on bacterial strains. Compound 2b showed the maximum efficacy against pathogenic bacteria and was identified as the lead molecule for further structural modifications.     

Effect of Curcuma longa tuber powder extract on size of silver nanoparticles prepared by green method

Biosynthesis of noble metal nanoparticles is a vast developing area of research. In the present study, silver nanoparticles (Ag-NPs) were synthesized from aqueous silver nitrate through a simple and biosynthetic route using water extract of Curcuma longa (C. longa) tuber powder, which acted simultaneousl as a reductant and stabilizery. The as-prepared samples are characterized using UV–Visible, XRD, TEM, SEM, EDXF, and FT-IR techniques. The formation of Ag-NPs is evidenced by the appearance of the signatory brown color of the solution and UV–vis spectra. Formation of Ag/C. longa was determined by UV–Vis spectroscopy where surface plasmon absorption maxima can be observed at 457–415 nm from the UV–Vis spectrum. The XRD analysis shows that the Ag-NPs are of a face-centered cubic structure. Well-dispersed Ag-NPs with anisotropic and isotropic morphology for 5, 10, and 20 mL of C. longa water extract having a size less than 10 nm are seen in TEM images. The optimum volume extraction to synthesize smallest particle size was 20 mL with mean diameter and standard division 4.90 ± 1.42 nm. FT-IR spectrum indicates the presence of different functional groups in capping the nanoparticles with C. longa. The zeta potential analysis results indicated that the charge of C. longa was negative and increased in Ag/C. longa emulsion with increasing of volumes of extract used (10–20 mL). The most needed outcome of this work will be the development of value-added products from C. longa for biomedical and nanotechnology-based industries.     

Improvement of the mechanical and rheological properties of HDPE/PET/MWCNT nanocomposites

High density polyethylene (HDPE)/poly (ethylene terephthalate) (PET) (90/10 wt.%) blends and HDPE/PET/multi-walled carbon nanotubes (MWCNTs) nanocomposites were prepared by melt mixing process, and the influence of MWCNTs on the mechanical and rheological properties of the nanocomposites was investigated. MWCNTs were added up to 5 wt.% in the HDPE/PET matrix. Transmission electron microscopy images reveal that the MWCNTs were homogeneously dispersed in the HDPE/PET matrix. Improvement of mechanical properties was observed by the addition of MWCNTs compared with HDPE/PET blends. Prominent increases in the complex viscosity and storage modulus of the nanocomposites were found with increasing MWCNT content.     

Noether Symmetries Versus Killing Vectors and Isometries of Spacetimes

Symmetries of spacetime manifolds which are given by Killing vectors are compared with the symmetries of the Lagrangians of the respective spacetimes. We find the point generators of the one parameter Lie groups of transformations that leave invariant the action integral corresponding to the Lagrangian (Noether symmetries). In the examples considered, it is shown that the Noether symmetries obtained by considering the Larangians provide additional symmetries which are not provided by the Killing vectors. It is conjectured that these symmetries would always provide a larger Lie algebra of which the KV symmetres will form a subalgebra. PACS: 04.25.-g, 02.20.Sv, 11.30.-j     

Microbial Cells with a Fe3O4 Doped Hydrogel Extracellular Matrix: Manipulation of Living Cells by Magnetic Stimulus

This study aims to develop an effective method to control motile microorganisms and enable their manipulation as functional ‘live micro/nano robots'. A novel strategy based on Fe₃O₄ nanoparticle‐doped alginate hydrogel is developed to fashion an artificial extracellular matrix (ECM) for microbial cells (e.g., Saccharomyces cerevisiae and Flavobacterium heparinum). During this strategy, a single layer of alginate hydrogel is coated around the microbial cells doped with Fe₃O₄ nanoparticles to form the alg‐mag‐cells. Transmission electron microscopy shows that Fe₃O₄ nanoparticles are uniformly distributed in the hydrogel shell. Together with maintaining the cell activity and metabolism, the hydrogel coated microbial cells demonstrate high magnetic responsiveness in an external magnetic field and are able to form micro‐scaled patterns using the magnetic template designed in this study. This strategy provides a building block to fabricate advanced biological models, medical therapeutic products, and non‐medical biological systems using different microorganisms.

     

Conducting polyaniline-rutile TiO2 nanocomposites for the development of high-k dielectric materials

Inorganic dielectrics encapsulated in an organic matrix are showing excellent promise as novel dielectric materials. In this work, firstly highly organized crystalline nanoparticles of rutile TiO₂ were synthesized by acid hydrolysis of titanium isopropoxide at room temperature. Then we developed a novel dielectric material consisting of highly organized rutile TiO₂/polyaniline (PAni) nanocomposites by in-situ chemical oxidative polymerization. The structural, morphological, conducting, and dielectric properties of the rutile TiO₂/PAni nanoparticles have been evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution-transmission emission microscopy (HR-TEM), four-point probe technique, CV (Capacitance versus Voltage), and Impedance analyzer. The nanocomposites show 70 times higher permittivity compared to rutile nanoparticles and much higher compared to anatase/PAni (ES) nanocomposites at 10 MHz. Large interfacial polarizations, nanostructure, and dopant levels are the key factors for the large dielectric constant of the nanocomposites. The rutile/PAni (ES) nanocomposites might see potential uses in super-capacitors, gate dielectric in transistors, and capacitive-type gas sensors.     

Efficient synthesis of some 3-arylisoquinolin-1(2H)-ones

A number of 3-arylisoquinolin-1(2H)-ones were efficiently prepared from the corresponding 3-aryl-isocoumarins by refluxing with methanamide. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1203–1208, August, 2008.