STRUCTURING ＆ RHEOLOGY OF MOLTEN POLYMER／CLAY NANOCOMPOSITES

The evolution and the origin of “solid-like state” in molten polymer/clay nanocomposites are studied. Using polypropylene/clay hybrid (PPCH) with sufficient maleic anhydride modified PP (PP-MA) as compatibilizer, well exfoliation yet solid-like state was achieved after annealing in molten state. Comprehensive linear viscoelasticity and non-linear rheological behaviors together with WAXD and TEM are studied on PPCH at various dispersion stages focusing on time,temperature and deformation dependencies of the “solid-like” state in molten nanocomposites. Based on these, it is revealed that the solid-structure is developed gradually along with annealing through the stages of inter-layer expansion by PP-MA,the diffusion and association of exfoliated silicate platelets, the formation of band/chain structure and, finally, a percolated clay associated network, which is responsible for the melt rigidity or solid-like state. The network will be broken down by melt frozen/crystallization and weakened at large shear or strong flow and, even more surprisingly, may be disrupted by using trace amount of silane coupling agent which may block the edge interaction of platelets. The solid-like structure causes characteristic non-linear rheological behaviors, e.g. residual stress after step shear, abnormal huge stress overshoots in step flows and, most remarkably, the negative first normal stress functions in steady shear or step flows. The rheological and structural arguments challenge the existing models of strengthened entangled polymer network by tethered polymer chains connecting clay particles or by chains in confined melts or frictional interaction among tactoids. A scheme of percolated networking of associated clay platelets, which may in band form of edge connecting exfoliated platelets, is suggested to explain previous experimental results.     

Residual stress and deformation during rapid cooling process in an epoxy plate

Residual stress in the epoxy plate during a rapid cooling process was measured by the layer removal method and calculated by the linear thermoviscoelastic theory considering specific volume relaxation. The relaxations of the tensile modulus and specific volume were measured by an Instron thermomechanical analyzer. When the starting temperature of the cooling process was near the glass transition temperature of the cured epoxy, the residual stress in the epoxy plate was smaller than when the starting temperature was higher than the glass transition temperature. However, the transient stress in the cured epoxy plate was higher when the starting temperature was near the glass transition temperature than when the starting temperature was higher than the glass transition temperature. The quenched epoxy plate was compressed in the direction parallel to the surface and expanded in the thickness direction.     

Mechanical properties of SBR-networks: I. Determination of crosslink densities by stress-strain-measurements

The tube model is applied for the treatment of stress-strain measurements on SBR networks. It is shown that this theory allows the separation of crosslink and constraint contributions to the stress-strain behavior and, also, a reliable determination of crosslink densities. The consideration of dynamical contributions is discussed and a special numerical method is developed.     

Vibronic intensities in centrosymmetric coordination compounds of the rare earths Part II. A vibronic crystal field-closure-ligand polarisation model and applications to the PrCl6 and UBr6 complex ions in octahedral symmetry

A symmetry adapted formalism to evaluate the vibronic intensities induced by the ungerade vibrational modes in centrosymmetric coordination compounds of the rare earths is put forward and applied to several selected electronic transitions of the PrCl³⁻₆ and UCl²⁻₆ complex ions in octahedral symmetry. This current model is based upon a modified symmetry adapted version of the combined vibronic crystal field-closure-ligand polarisation approach. This model differs from that developed in Part I of this series, in that for the vibronic crystal field contribution to the total transition dipole moment, the closure procedure is employed rather than the utilisation of a truncated basis set for the central metal intermediate electronic states. A criterion is introduced to choose an appropriate set of phases for both the electronic and the vibrational coordinates so that to ensure the right sign for the interference term (which couples together both the vibronic crystal field and the vibronic ligand polarisation contributions to the total transition dipole moment). We have focused our attention on the modulation of the intermolecular force field and a version of a modified general valence force field has been adopted. The reasons for using this formalism rather than the superposition model (SM) are fully discussed in the text. Finally, it is shown that the agreement with experiment is satisfactory for most of the components of the transitions studied, despite the apparent simplicity of our model calculation. General master equations applicable to any f^N electronic configurations are derived to show the utility and flexibility of this current formalism.     

Chemical-effect variation of Kβ/Kα X-ray intensity ratios in 3d elements

Chemical effects on Kβ/Kα X-ray intensity ratios for some Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn compounds are studied experimentally. The X-ray spectra were measured by using a Si (Li) solid state detector with high resolution. The vacancies were produced by heavily filtered ²⁴¹Am gamma rays. It is found that the Kβ/Kα X-ray intensity ratios measured with compounds deviated up to 43% from the corresponding values of the pure elements. The values for pure elements are compared with the other experimental and with theoretical values.     

Rheology of polystyrene solutions around the coil overlapping concentration: A phenomenological description of stresses in simple shear flow

Linear viscoelasticity behavior is described with the sum of two terms for polystyrene solutions in tricresyl phosphate around the coil overlapping concentration (K. Osaki, T. Inoue, & T. Uematsu, J Polym Sci Part B: Polym Phys 2001, 39, 211). One is a Rouse–Zimm (RZ) term represented by the Zimm theory with arbitrarily chosen values of the hydrodynamic interaction parameter and the longest relaxation time (τ_RZ). The other (the L term) consists of a relaxation mode with a single relaxation time (τ_L > τ_RZ) and a high‐frequency limiting modulus proportional to the square of the concentration. In this study, we describe the viscosity (η) and first normal stress coefficient (Ψ₁) in steady shear with simple formulas. The stress due to the L term is assumed to be given by a Kaye, Bernstein, Kearsley, and Zapas (K‐BKZ) equation with the damping function h(γ) = (1 + 0.2γ²)^?1/2, where γ is the magnitude of shear. Contributions to η and Ψ₁ from the RZ term are derived from the RZ model, in which the relaxation time in steady flow is given by τ_st = τ + (τ_RZ ? τ)/(1 + 0.35τ_RZ γ˙) instead of τ_RZ. Here, γ˙ is the rate of shear, and τ is the τ_RZ value at the infinite dilution limit. η and Ψ₁ at various concentrations for two polystyrene samples (with molecular weights of 2890 and 8420 kg mol^?1) are well described with parameters derived from dynamic viscoelasticity. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1038–1045, 2002     

Nitrotyrosine-modified proteins and oxidative stress induced by diesel exhaust particles

Protein tyrosine nitration is a post-translational modification that occurs under conditions of oxidative stress and may play a role in the pathogenesis of diseases such as asthma. Through their ability to generate reactive oxygen species in macrophages and epithelial cells, particulate pollutants, such as diesel exhaust particles (DEPs), may lead to a worsening of the asthmatic condition. In this study, we looked for evidence of oxidative modification of proteins in RAW 264.7 cell line treated with DEP chemicals. We show that the induction of oxidative stress is accompanied by 53 newly expressed proteins which are suppressed by a thiol antioxidant, N-acetylcysteine. These include antioxidant enzymes, pro-inflammatory components, and products of intermediary metabolism. In addition, inducible nitric oxide synthase (iNOS) was identified as a biologically relevant oxidative stress protein that is induced concurrent with increased NO production and protein tyrosine-nitration in DEP-exposed RAW 264.7 cells. Utilizing two-dimensional gel electrophoresis, anti-nitrotyrosine immunoblotting, and mass spectrometry led to the identification of an additional ten nitrotyrosine modified proteins, including oxidative stress proteins involved in intermediary metabolism (e.g., GAPDH and enolase), antioxidant defense (e.g., MnSOD) and inhibition of proteosomal activity (e.g., Hsp 90alpha). These oxidative proteins may serve as markers for oxidative stress generation in vivo.     

Prepared Low Stress Cubic Boron Nitride Film by Physical Vapor Deposition

We present low stress cubic boron nitride (cBN) films with a transition layer deposited on the metal alloy substrates by tuned substrate radio-frequency magnetron sputtering. The films were characterized by Fourier transform infrared spectroscopy and transmission electron microscopy (TEM). The IR peak position of cubic boron nitride at 1006.3 cm⁻¹, which is close to the stressless state, indicates that the film has very low internal stress. The TEM image shows that pure CBN phase exists on the surface of the film. Several phases of boron nitride were found at the medium implantation dose. It is believed that the transition from the low ordered phases to cBN phase occurred during implantation.     

助熔剂对Y3Al5O12：Ce荧光粉性能的影响

在还原气氛下采用高温固相反应法合成了白光LED用黄色荧光粉Y3Al5O12:Ce(YAG:Ce)研究了助熔剂对YAG：Ce荧光粉发光特性的影响，。XRD的测量结果表明加入合适的助熔剂有利于YAG:Ce荧光粉的晶化，并且不引入杂相，选择BaF2和H3BO3同时使用效果要好于单独使用一种助熔剂，助熔剂的加入可增大YAG：Ce荧光粉的激发和发射光谱强度，并能有效降低荧光粉的中心粒径（D50）控制粉体的粒径分布，适用于白光LED的制造。     

Age-dependent variations of cell response to oxidative stress: proteomic approach to protein expression and phosphorylation

We investigated the protein profiles of variously aged rat astrocytes in response to oxidative stress. After H2O2-exposure of cells at 100 microM for 30 min, the relative intensity of ten protein spots changed on two-dimensional (2-D) gels compared with control gels after silver staining. Matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) analysis after in-gel digestion revealed that six of these spots corresponded to three kinds of proteins, each of which was composed of a protein and its modified form with a different isoelectric point (pI). These three proteins were identified as peroxiredoxins (PRDXs) II and III, and calpactin I light chain (p11). H2O2-exposure increased the intensity of the spot with lower pI and simultaneously decreased that of the spot with higher pI for both PRDXs II and III. In addition, the expression of annexin VII, S-adenosyl-L-homocysteine hydrolase, elongation factor II fragment (EF-II), and adenosine deaminase was increased by H2O2-exposure in astrocytes from variously aged rats. Using the Pro-Q Diamond staining, heat shock protein 60 kDa (Hsp 60) and alpha-tubulin were observed to be phosphorylated upon H2O2-exposure. While phosphorylation of alpha-tubulin was correlated positively with age, the changes in abundance of ten protein spots as described above were independent of age. These results suggest that aging does not suppress the responses aimed at limiting injury and promoting repair brought about by severe oxidative stress, and might affect cell dynamics including the formation of microtubules.