Electrorheology of Multiwalled Carbon Nanotube/Poly(methyl methacrylate) Nanocomposites

Summary: Multiwalled carbon nanotube (MWNT) nanocomposites dispersed in a poly(methyl methacrylate) (PMMA) matrix were prepared via suspension polymerization, in which radicals induced on the outer wall of the MWNTs by 2,2′‐azoisobutyronitrile initiate the grafting of PMMA. The synthesized MWNT/PMMA nanocomposite particles were found to have a spherical shape and exhibit a high electrical conductivity, mainly as a result of the carbon nanotubes. A suspension was prepared with MWNT/PMMA particles in insulating silicone oil and its electrorheological properties were investigated by controlling applied direct current (DC) electric field strengths.

Flow curve possessing a region analogous to the coexistence curve.     

The Molecular Spreading of Nonpolar Perfluoropolyether Films on Amorphous Carbon Surfaces

The spreading mechanism of nonpolar perfluoropolyether films on carbon surfaces is examined in the mesoscopic regime, including both submonolayer and multilayer films. For the submonolayer film, adsorption-desorption is a main mechanism for spreading, and the surface diffusion coefficients increase as the film thickness increases. The driving force for the spreading in the submonolayer regime is the gradient of the disjoining pressure, which is described by the two-dimensional virial equation. For the multilayer film regime, the spreading characteristics are determined by the molecular weight and the disjoining pressure gradient, which is assumed to be purely van der Waals in nature. We adopt a partial slip boundary condition to analyze the multilayer film, which qualitatively explains the dependence of the surface diffusion coefficient on film thickness. Copyright 2000 Academic Press.     

螺二邻二亚甲基噻吩和环二邻二亚甲基噻吩的合成

Errede等曾利用氢氧化邻甲基苄基三甲基铵的热解制得螺二邻二亚甲基苯、环二邻二亚甲基苯和聚邻二亚甲基苯。Winberg等人对噻吩的季铵碱的热解有所研究,但未能触及活泼的中间体2,3-二亚甲基-2,3-二氢化噻吩Ⅷ及其二聚体螺环化合物和环状化合物。     

Ab initio SCF calculations of the linear infinite chain of LiH according to the pseudo-lattice method

The pseudo-lattice (PL) method has been reformulated for ab initio self-consistent-field (SCF) calculations. The translational symmetries of infinite systems have been applied to the finite model chain by manipulating all the intramolecular and intermolecular Fock matrices. The nuclear repulsion energy has been corrected accordingly. The method has been tested for the linear chain of lithium hydride under the constraint of equidistance between all neighboring lithium and hydrogen atoms. The calculated results of the infinite chain have been compared with those of finite chains of lithium hydride under the same geometric constraint. The equilibrium geometries, band structures, intermolecular stabilization energies and potential curves have been studied. It is found that the infinite systems cannot be described by considering only first nearest neighbor interactions, and the intermolecular interactions must be considered at least up to third nearest neighbors in order to obtain accurate value of force constant of infinite systems. We can conclude from band structures of infinite chains that the boundary effect of the finite model chain is effectively removed by the PL method.     

Preparation and Rheological Characteristics of Solvent‐Cast Poly(ethylene oxide)/Montmorillonite Nanocomposites

The organophilic montmorillonite clay and poly(ethylene oxide) (PEO) nanocomposites were intercalated by a solvent casting method using chloroform as the cosolvent. The prepared nanocomposites were characterized by an X‐ray diffraction method to examine their microstructure. Rheological properties of both the PEO/clay nanocomposites and the immiscible PEO/clay blends were investigated via a rotational rheometer in steady shear mode with a parallel plate geometry. The shear thinning viscosity data were fitted with the Carreau model, which showed that steady shear viscosity increases with increasing clay loading. The hysteresis phenomenon is observed to be enhanced with clay loading. PEO/clay nanocomposites exhibit higher zero‐shear‐rate viscosity and sharper shear thinning behaviors than immiscible PEO/clay blends.     

Conformational preferences of proline oligopeptides

A conformational study on the terminally blocked proline oligopeptides, Ac-(Pro)(n)()-NMe(2) (n = 2-5), is carried out using the ab initio Hartree-Fock level of theory with the self-consistent reaction field method in the gas phase and in solutions (chloroform, 1-propanol, and water) to explore the preference and transition between polyproline II (PPII) and polyproline I (PPI) conformations depending on the chain length, the puckering, and the solvent. The mean differences in the free energy per proline of the up-puckered conformations relative to the down-puckered conformations for both diproline and triproline increases for the PPII-like conformations and decreases for the PPI-like conformations as the solvent polarity increases. These calculated results indicate that the PPII-like structures have preferentially all-down puckerings in solutions, whereas the PPI-like structures have partially mixed puckerings. The free energy difference per proline residue between the PPII- and PPI-like structures decreases as the proline chain becomes longer in the gas phase but increases as the proline chain becomes longer in solutions and the solvent polarity increases. In particular, our calculated results indicate that each of the proline oligopeptides can exist as an ensemble of conformations with the trans and cis peptide bonds in solutions, although the PPII-like structure with all-trans peptide bonds is dominantly preferred, which is reasonably consistent with the previously observed results. In diproline Ac-(Pro)(2)-NMe(2), the rotational barrier to the cis-to-trans isomerization for the first prolyl peptide bond increases as the solvent polarity increases, whereas the rotational barrier for the second prolyl peptide bond does not show the monotonic increase as the solvent polarity increases. When the rotational barriers for these two prolyl peptide bonds were compared, it could be deduced that the conformational transition from PPI with the cis peptide bond to PPII with the trans peptide bond is initiated at the C-terminus and proceeds to the N-terminus in water. This is consistent with the results from NMR experiments on polyproline in D(2)O but opposite to the results from enzymatic hydrolysis kinetics experiments on polyproline.     

Metabolite Profiling to Monitor Organochlorine Pesticide Exposure in HepG2 Cell Culture

Gas chromatography coupled with time of flight mass spectrometry (GC/MS-TOF) was used to profile endogenous metabolites in HepG2 cell cultures to assess the metabolic changes induced by exposure to different organochlorine pesticides, their mixtures and controls (endosulfan, lindane, DDT and aldrin). Cells were cultured in DMEM with Glutamax at 37 °C with 5 % CO₂ for 72 h and then exposed to each pesticide, pesticide mixture or DMSO (as a control) for 24 h, and finally, endogenous metabolites were extracted and analyzed using GC/MS-TOF. The experiment was repeated six times under the same cell passage and culture conditions. PCA, PLS-DA and ROC were performed to analyze the GC/MS-TOF data and identify potential biomarkers. Thirty-five explanatory metabolites were found in both PCA and PLS-DA models, where Q ² was 0.86 and R ² was 0.98. Univariate and multivariate ROC showed potential biomarkers for each treatment, suggesting a general toxic mechanism for organochlorine pesticides that is specific for each type of compound. These results confirmed the effect of OCPs in sugar and amino acid metabolism that are linked with the function of cytochrome P450 in reductive dechlorination and oxidative stress.

     

Effects of Hydrogen-Enrichment on Flame-Holding of Natural Gas Jet Flames in Crossflow at Elevated Temperature and Pressure

Flow, Turbulence and Combustion - The effect of hydrogen ( $$\mathrm {H}_{\mathrm {2}}$$ ) enrichment on the flame-holding characteristics of two natural gas jet flames in crossflow is investigated...