Analysis of the nonisothermal crystallization kinetics in three linear aromatic polyester systems

Melt or cold crystallization kinetics has a strong bearing on morphology and the extent of crystallization, which significantly affects the physical properties of polymeric materials. Nonisothermal crystallization kinetics are often analyzed by the classical Johnson–Mehl–Avrami–Kolmogorov (JMAK) model or one of its variants, even though they are based on an isothermal assumption. As a result, during the nonisothermal (e.g. constant heating or cooling rate) crystallization of polymeric material, different sets of model parameters are required to describe crystallization at different rates, thereby increasing the total number of model parameters. In addition, due to the uncorrelated nature of these model parameters with the cooling or heating rate, accurate modeling at any intermediate condition is not possible. In the present work, these two limitations of the conventional approach have been eliminated by exhibiting the existence of a functional relationship between cooling or heating rate and effective activation energy during nonisothermal melt or cold crystallization in three linear aromatic polyesters. Furthermore, it has been shown that when the JMAK model is used in conjunction with this functional relationship, it is possible to precisely predict the experimental nonisothermal melt or cold crystallization kinetics at any linear cooling or heating rate with a single set of model parameters.     

Electrochemical supercapacitive performance of potentiostatically cathodic electrodeposited nanostructured MnO2 films

Journal of Solid State Electrochemistry - Nanostructured MnO2 films were prepared via cathodic electrodeposition under potentiostatic condition. X-ray diffraction (XRD) analyses reveal that the...     

Revisiting aryl amidine synthesis using metal amide and/or ammonia gas: Novel molecules and their biological evaluation

Amidines, due to their unique biocompatibility and desirable physical characteristics, have been the functionality of choice as a scaffold for large number of drug synthesis. But still synthesis of amidines in the presence of other active functional groups or pharmacophore, remained a challenge. In this work, a simple and reliable protocol for conversion of nitrile-amide to unsubstituted amidine–amide is developed using metal amide and/or ammonia gas. The scope and efficiency of this synthetic strategy are demonstrated on several substrates which differ in functional groups will be discussed. In this process, 10 novel aryl amidines in good yields (upto 85%) were synthesized. Biological evaluation revealed that compound 4-(aminoiminomethyl)-N-(2-furanyl methyl) benzamide (IC₅₀?=?9?µM) and 4-(aminoiminomethyl)-N-(3-pyridinylmethyl) benzamide (73.36% growth inhibition) showed moderate efficacy for cancer cells.     

Fast compressional wave attenuation and dispersion due to conversion scattering into slow shear waves in randomly heterogeneous porous media

Within the viscosity-extended Biot framework of wave propagation in porous media, the existence of a slow shear wave mode with non-vanishing velocity is predicted. It is a highly diffusive shear mode wherein the two constituent phases essentially undergo out-of-phase shear motions (slow shear wave). In order to elucidate the interaction of this wave mode with propagating wave fields in an inhomogeneous medium the process of conversion scattering from fast compressional waves into slow shear waves is analyzed using the method of statistical smoothing in randomly heterogeneous poroelastic media. The result is a complex wave number of a coherent plane compressional wave propagating in a dynamic-equivalent homogeneous medium. Analysis of the results shows that the conversion scattering process draws energy from the propagating wave and therefore leads to attenuation and phase velocity dispersion. Attenuation and dispersion characteristics are typical for a relaxation process, in this case shear stress relaxation. The mechanism of conversion scattering into the slow shear wave is associated with the development of viscous boundary layers in the transition from the viscosity-dominated to inertial regime in a macroscopically homogeneous poroelastic solid.     

Rapid discovery of potent siRNA-containing lipid nanoparticles enabled by controlled microfluidic formulation

The discovery of potent new materials for in vivo delivery of nucleic acids depends upon successful formulation of the active molecules into a dosage form suitable for the physiological environment. Because of the inefficiencies of current formulation methods, materials are usually first evaluated for in vitro delivery efficacy as simple ionic complexes with the nucleic acids (lipoplexes). The predictive value of such assays, however, has never been systematically studied. Here, for the first time, by developing a microfluidic method that allowed the rapid preparation of high-quality siRNA-containing lipid nanoparticles (LNPs) for a large number of materials, we have shown that gene silencing assays employing lipoplexes result in a high rate of false negatives (~90%) that can largely be avoided through formulation. Seven novel materials with in vivo gene silencing potencies of >90% at a dose of 1.0 mg/kg in mice were discovered. This method will facilitate the discovery of next-generation reagents for LNP-mediated nucleic acid delivery.     

Optical and electrical studies on spray deposited ZnO thin films

ZnO thin films were prepared by spray pyrolytic decomposition of zinc acetate onto a glass substrate. These films were analyzed for the optical and electrical properties. Optical studies show that in these films the electronic transition is of the direct transition type. The optical energy gap for the films of different thicknesses is estimated to be in the range 2.98 – 3.09 eV. Electrical studies indicate that the films exhibit thermally activated electronic conduction and the activation energies are found to be dependent on the film thickness. The complex impedance measurements were carried out over a wide range of frequencies at room temperature (300 K). All the impedance spectra contain only a single arc, but the arc has a non‐zero intersection with the real axis in the high frequency region. Also, the arc has its centre lying below with the real axis which indicates the multirelaxation behavior of the films. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Luminescent piano-stool complexes incorporating 1-(4-cyanophenyl)imidazole: synthesis, spectral, and structural studies

Three novel luminescent piano-stool arene ruthenium complexes of general formula [(eta(6)-arene)RuCl(2)(CPI)] (eta(6)-arene = benzene, 1, p-cymene, 2, and hexamethylbenzene, 3; CPI=1-(4-cyanophenyl)imidazole were prepared. The molecular structures of 2 and 3 were determined crystallographically. Reaction of 1-3 with EPh(3) (E = P, As, or Sb) and N-N donor bases such as 2,2'-bipyridine and 1,10-phenanthroline afforded cationic mononuclear complexes of general formula [(eta(6)-arene)RuCl(CPI)(EPh(3))](+) (eta(6)-arene = C(6)H(6), E = P (1a), E = As (1b), E = Sb(1c); eta(6)-arene = C(10)H(14), E = P (2a), E = As (2b), E = Sb (2c); eta(6)-arene = C(6)Me(6), E = P (3a), E = As (3b), E = Sb (3c)) and [(eta(6)-arene)Ru(N-N)(CPI)](2+) (eta(6)-arene = C(6)H(6), N-N = bipy (1d), N-N = phen (1e); eta(6)-arene = C(10)H(14), N-N = bipy (2d), N-N = phen (2e); eta(6)-arene = C(6)Me(6), N-N = bipy (3d), N-N = phen (3e)). Molecular structures of 1a and 2a were also confirmed by X-ray crystallography. Structural studies of the complexes 2, 3, 1a, and 2a supported coordination of CPI through the imidazole nitrogen and the presence of a pendant nitrile group. Structural data also revealed stabilization of crystal packing in the complexes 2, 3, and 2a by C-H...X (X = Cl, F) type inter- and intramolecular interactions and in complex 1a by pi-pi stacking. Moreover, neutral homonuclear bimetallic complexes 2f,g were prepared by using complex 2 as a metallo-ligand, where CPI acts as a bridge between two metal centers. Emission spectra of the mononuclear complexes [(eta(6)-arene)RuCl(2)(CPI)] and its derivatives exhibited intense luminescence when excited in the metal to ligand charge-transfer band.     

Effect of precursors on structure, optical and electrical properties of chemically deposited nanocrystalline ZnO thin films

Nanocrystalline ZnO thin films were chemically deposited on glass substrates using two different precursors namely, zinc sulphate and zinc nitrate. XRD studies confirm that the films are polycrystalline zinc oxide having hexagonal wurtzite structure with crystallite size in the range 25-33 nm. The surface morphology of film prepared using zinc sulphate exhibits agglomeration of small grains throughout the surface with no visible holes or faulty zones, while the film prepared using zinc nitrate shows a porous structure consisting of grains with different sizes separated by empty spaces. The film prepared using zinc sulphate shows higher reflectance due to its larger refractive index which is related to the packing density of grains in the film. Further, the film prepared using zinc sulphate is found to have normal dispersion for the wavelength range 550-750 nm, whereas the film prepared using zinc nitrate has normal dispersion for the wavelength range 450-750 nm. The direct optical band gaps in the two films are estimated to be 3.01 eV and 3.00 eV, respectively. The change in film resistance with temperature has been explained on the basis of two competing processes, viz. thermal excitation of electrons and atmospheric oxygen adsorption, occurring simultaneously. The activation energies of the films in two different regions indicate the presence of two energy levels - one deep and one shallow near the bottom of the conduction band in the bandgap.     

The precipitation of barium sulphate and chromate powders from aqueous solution with slow development of supersaturation. Crystal numbers and final crystal sizes

The precipitations of barium sulphate and chromate were studied by slow addition of anion to metal cation solution at 20°C, to give final equivalent metal salt solutions; the final solute concentrations (C_fin) were varied from 0.002 to 0.30 mol l⁻¹ while the rates (R) of addition of anion were varied from 10⁻⁴ to 10⁻² ion l⁻¹. At first, mainly heterogeneous nuclei formed continuously during induction periods; then, as the metal salt concentration in solution increased, homogeneous nucleation soon predominated. This second nucleation process probably attained its maximum rate when the metal salt concentration in solution reached its maximum value (C_max) and then probably terminated quite rapidly. Some further nuclei also formed during the growth process when crystal growth was prolonged. The final nucleus numbers (N), and thence the crystal numbers for slow precipitations from very dilute solutions were then rather higher than the number N ∞ (het) of heterogeneous nuclei in solution: nucleus numbers then increased with increasing mixing rate according to the relation, (where β = 0.7–0.9) (where β = 0.7–0.9). The final average crystal lengths of any precipitate were then 2 to 40 times the sizes noted for rapid precipitation from equivalent solutions of the same concentration: generally, final lengths varied with mixing rate according to the relation, .