Landau theory description of observed isotropic to anisotropic phase transition in mixed clay gels

A characteristic new cooperative dehydration transition, in 1:1 Laponite-MMT cogel, was observed at T(c) ≈ 60 °C, a temperature at which the storage modulus (G(')) and depolarization ratio (D(p)) showed sharp increase, and the isotropic cogel turned into an anisotropic one. The dehydration dynamics could be described through power-law relations: G(') ～ (T(c)-T)(-γ) and D(p) ～ (T(c)-T)(-β) with γ ≈ β = 0.40 ± 0.05. The x-ray diffraction data revealed that the crystallite size decreased from 17 nm (at 20 °C) to 10 nm (at 80 °C) implying loss of free and inter-planar water. When this cogel was spontaneously cooled below T(c), it exhibited much larger storage modulii values which implied the existence of several metastable states in this system. This phase transition could be modeled through Landau theory, where the depolarization ratio was used as experimental order parameter (ψ). This parameter was found to scale with temperature, as ψ ～ (T(c)-T)(-α), with power-law exponent α = 0.40 ± 0.05; interestingly, we found α ≈ β ≈ γ.     

New exact solutions of the Einstein-Maxwell equations for magnetostatic fields

The symmetry reduction method based on the Fr′echet derivative of differential operators is applied to investigate symmetries of the Einstein-Maxwell field equations for magnetostatic fields, which is a coupled system of nonlinear partial differential equations of the second order. The technique yields invariant transformations that reduce the given system of partial differential equations to a system of nonlinear ordinary differential equations. Some of the reduced systems are further studied to obtain the exact solutions.     

Diorgano-gallium and -indium complexes with salen ligands: Synthesis, characterization, crystal structure and C-C coupling reactions

The reactions of triorgano-gallium and -indium etherate with salen ligands in benzene afforded complexes of the type [R₂MOC₆H₄CR′NCH₂-]₂, (R/M/R′ = Me/Ga/H (1), Et/Ga/H (2), Me/In/H (3), Et/Ga/Me (4)) in nearly quantitative yields. These complexes have been characterized by elemental analysis, IR, UV-Vis, NMR (¹H and ¹³C{¹H}) and mass spectral data. The organogallium complexes showed photoluminescence in blue-green region. The complex, [(Me₂Ga)₂(O-(C₆H₄)CHN-CH₂-)₂] on recrystallization from benzene-hexane and dichloromethane gave orthorhombic and monoclinic forms, respectively. Both the forms are dimeric with gallium atoms acquiring a distorted tetrahedral configuration defined by two methyl groups, phenolate oxygen and azomethene nitrogen. The complexes [(Me₂Ga)₂(O-(C₆H₄)CHN-CH₂-)₂] and [(Me₂In)₂(O-(C₆H₄)CHN-CH₂-)₂] have been employed as alkylating agent for C-C coupling reaction of 1-bromonaphthalene in presence of PdCl₂(PPh₃)₂.     

A comparative study of pure and potassium doped cadmium mercury thiocyanate single crystals grown in silica gel

Pure and potassium doped cadmium mercury thiocyanate single crystals have been obtained from silica gel by the process of diffusion. The X‐ray diffraction studies reveal the crystal lattice of both pure and doped crystals to be tetragonal. The crystalline perfection of the grown crystals were investigated by high resolution X‐ray diffraction analysis and the quality of the crystals are found to be extremely good. Transmission and Fourier transform infrared spectra were recorded for the grown crystals. The TG/DTA analyses show that the crystals are highly thermally stable. The mechanical strength of the crystals were studied by Vickers microhardness test and a study of their second harmonic generation efficiency in comparison with urea has been made by performing Kurtz powder test. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study of the effect of SHI irradiation on nanocrystalline vacancy doped (La,Sr)(Mn,Fe)O system and its comparison with hydrostatic pressure using Mössbauer spectroscopy

The swift heavy ion irradiated La_0.9Mn_0.8Fe_0.2O₃ (La-deficient) system with 200 Mev Ag^16?+? ion beam at fluence 5 × 10¹² ions/cm² was studied with X-ray diffraction (XRD) and Mössbauer spectroscopic measurements. Comparison of Mössbauer parameters with those of unirradiated sample showed an increase in line width on irradiation which may be due to reduction in particle size as well as due to creation of defects. An increase in quadrupole splitting with no appreciable change in isomer shift showed ion-induced structural disorder in the material after irradiation. An attempt is made to compare the effect of fluence with the hydrostatic pressure on the sample.     

Water-soluble nanoparticles from random copolymer and oppositely charged surfactant, 3a. Nanoparticles of poly(ethylene glycol)-based cationic random copolymer and fatty acid salts

In this report, we investigate the nanoparticle formation between random copolymers (RCPs) of methoxy-poly(ethylene glycol) monomethacrylate (MePEGMA) and (3-(methacryloylamino)propyl)trimethylammonium chloride (MAPTAC) and oppositely charged natural surfactants, sodium oleate and sodium laurate, using turbidimetric titration, steady-state fluorescence, dynamic light scattering, and electron microscopy. Though sodium oleate and sodium laurate are sparingly soluble in water, the nanoparticle complexes formed between the RCPs and these surfactants are soluble in the entire range of compositions studied here, including the stoichiometric electronetural complexes. The spherical nature of these nanoparticle complexes is revealed by electron microscopic (EM) analysis. Dynamic light scattering (DLS) showed that the average diameters of the nanoparticles are in the range 50 to 150 nm, which is supported by EM analysis. Pyrene fluorescence experiments suggested that these soluble nanoparticles have hydrophobic cores, which may solubilize hydrophobic drug molecules. The polarity index (I(1)/I(3)) obtained from the pyrene fluorescence spectra and the conductometric measurements showed that the critical concentration of fatty acid salts needed to obtain nanoparticles are in the order of 10(-4) M. Further, the complexation of such poorly water-soluble amphiphilic surfactants with polymers offers a useful method for the immobilization of hydrophobic compounds towards water-soluble drug carrier formulations. The formation of water-soluble nanoparticles by the self-assembly of fatty acid salts upon interacting with oppositely charged poly(ethylene glycol)-based polyions.     

A convenient synthesis of methylindium(III) dithiolate complexes—precursors for indium sulfides

Methylindium(III) dithiolate complexes of the general formulae [Me₂In(S^∩S)] ( 1 ) and [MeIn(S^∩S)₂] ( 2 ) [S^∩S = (EtO)₂PS₂^?, (PrⁱO)₂PS₂^?, Et₂NCS₂^?, , O(CH₂CH₂)₂NCS₂^?, EtOCS₂^? and PrⁱOCS₂^?] have been isolated conveniently by the reaction of Me₃In·OEt₂ with In(S^∩S)₃ ( 3 ) in an appropriate stoichiometry. Both 1 and 2 have been characterized by indium analysis, IR, NMR (¹H, ¹³C{¹H} and ³¹P{H}) and mass spectral data. NMR data of 3 are also included for comparison. The Me–In and S^∩S resonances are sensitive to the number of methyl groups attached to indium metal. The mass spectral data indicate that these complexes are monomeric in nature. The thermal behavior of a few complexes has been investigated. The xanthate and dithiocarbamate complexes on pyrolysis under dynamic vacuum or flowing nitrogen atmosphere gave either In₂S₃ or a mixture of InS, In₂S₃ and In₆S₇, which were characterized using EDAX and powder XRD. Copyright © 2005 John Wiley & Sons, Ltd.     

An energy efficient distributed queuing random access (EE-DQRA) MAC protocol for wireless body sensor networks

Wireless Networks - In wireless sensor networks, a significant amount of energy is consumed by the sensor nodes during data packet transmission and reception. An IEEE 802.15.4 MAC protocol is not...