Dynamically vulcanized ethylene propylene diene terpolymer/nylon thermoplastic elastomers

A thermoplastic elastomer (TPE) of ethylene propylene diene terpolymer (EPDM) and nylon with excellent mechanical properties was prepared by dynamic vulcanization. The effects of the curing systems, compatibilizer, nylon content and reprocessing on the mechanical properties of EPDM/nylon TPEs were investigated in detail. Experimental results indicate that maleic anhydride (MAH) grafted EPR has a better performance in compatibilizing the EPDM/nylon blends compared with other compatibilizers containing acid group. Tensile strength and elongation at break go through a maximum value at a compatibilizer resin content (on total rubber dosage) of 20%. EPDM/nylon TPE using sulfur as curative has higher tensile strength and elongation than that of TPE using phenolic resin or peroxide as curatives. Tensile strength and elongation at break increase with increasing nylon content. Scanning electron microscopy results show that rubber particles distributed at an average size of 1 μm in dynamic vulcanized EPDM/MAH-g-EPR/nylon TPE.     

Vapor-liquid equilibrium properties for confined binary mixtures involving CO2, CH4, and N2 from Gibbs ensemble Monte Carlo simulations

The effects of solid-fluid interactions on the vapor-liquid phase diagram,coexistence density,relative volatility and vaporization enthalpy have been investigated for confined binary systems of CO 2-CH 4,CO 2-N 2 and CH 4-N 2.The Gibbs ensemble Monte Carlo(GEMC) simulation results indicate that the confinement and the solid-fluid interaction have significant influences on the vapor-liquid equilibrium properties.The confinement and the strength of the solid-fluid interaction make the p-x i phase diagram move to higher pressure regions.They also make the two-phase region become narrower for each binary mixture.The strength of the solid-fluid interactions can cause increases in the coexistence liquid and vapor densities,and cause the decrease of the relative volatility and the vaporization enthalpy for the systems studied.As the pore width is decreased,the two-phase region of the binary mixture becomes narrower.     

Iron-catalyzed cascade reaction of ynone with o-aminoaryl compounds: a Michael addition-cyclization approach to 3-carbonyl quinolines

An efficient iron-catalyzed cascade Michael addition-cyclization of o-aminoaryl compounds including o-aminoaryl aldehydes, o-aminoaryl ketones, and o-aminobenzyl alcohols with ynones for the synthesis of 3-carbonyl quinolines is reported. The reactions proceed to afford 3-carbonyl quinoline derivatives with or without substituent at the C-4 position in good to high yields using Iron(III) chloride hexahydrate as the catalyst in the air.     

Simulation study on dynamics of A- to B-form transition in aqueous DNA solution: Effect of alkali metal counterions

DNA and its conformational transition can be used to design nanometer-scale structures, nano-tweezers and nanomechanical devices. Experiments and molecular simulations have been used to study the concentration effect on the A-DNA→B-DNA conformational transition, but a systematical investigation on counterion effect on the dynamics of this transition has not been reported up to now. In present work, restrained and unrestrained molecular dynamics (MD) simulations have been performed to characterize the stability of DNA conformations and the dynamics of A-DNA→B-DNA transitions in aqueous solutions with different alkali metal counterions. The DNA duplex d(CGCGAATTCGCG)₂, coion Cl^? and counterions Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ as well as water molecule were considered using the PARM99 force field in the AMBER8 package. It was found that B-form DNA is more stable than A-form DNA in aqueous electrolyte solutions with different alkali metal counterions. Increasing KCl concentration in solution hinders the A-DNA→B-DNA transition and the transition times for different alkali metal counterions conform to neither the simple sequence related to naked ion size nor to hydrated diameter, but an apparently abnormal sequence of K⁺ < Rb⁺ < Cs⁺ < Na⁺ < Li⁺. This abnormal sequence can be well understood in terms of an electrostatic model based on the effective cation diameters and the modified mean-spherical approximation (MMSA). The present results provide valuable information for the design of DNA-based nanomaterials and nanodevices.     

Molecular dynamics simulation of the A-DNA to B-DNA transition in aqueous RbCl solution

Unrestrained molecular dynamics (MD) simulations have been carried out to characterize the stability of DNA conformations and the dynamics of A-DNA→B-DNA conformational transitions in aqueous RbCl solutions. The PARM99 force field in the AMBER8 package was used to investigate the effect of RbCl concentration on the dynamics of the A→B conformational transition in the DNA duplex d(CGCGAATTCGCG)2 . Canonical Aand B-form DNA were assumed for the initial conformation and the final conformation had a length per complete turn that matched the canonical B-DNA. The DNA structure was monitored for 3.0 ns and the distances between the C5′ atoms were obtained from the simulations. It was found that all of the double stranded DNA strands of A-DNA converged to the structure of B-form DNA within 1.0 ns during the unrestrained MD simulations. In addition, increasing the RbCl concentration in aqueous solution hindered the A→B conformational transition and the transition in aqueous RbCl solution was faster than that in aqueous NaCl solution for the same electrolyte strength. The effects of the types and concentrations of counterions on the dynamics of the A→B conformational transition can be understood in terms of the variation in water activity and the number of accumulated counterions in the major grooves of A-DNA. The rubidium ion distributions around both fixed A-DNA and B-DNA were obtained using the restrained MD simulations to help explain the effect of RbCl concentration on the dynamics of the A→B conformational transition.     

受限狭缝中CO_2-CH_4体系的汽液相平衡性质

受限条件下CO2-CH4体系的相平衡性质对化工工艺过程的设计具有非常重要的意义.采用Gibbs系综Monte Carlo模拟,对220K下CO2-CH4体系在主体相和受限狭缝中的相平衡性质进行了系统地研究.通过主体相模拟与实验结果比较,验证了流体分子势能参数的合理性;通过改变狭缝壁面原子的能量参数,研究了受限环境对CO2-CH4体系汽液相平衡性质的影响.与主体相相比,在硬壁狭缝中,CO2-CH4体系的露点压力增加,泡点压力降低,压力-组成相图变窄,且体系更容易达到超临界状态;在吸引狭缝中,随壁面原子能量参数的增大,CO2-CH4体系的压力-组成相图上移,临界点处CH4的摩尔分数减小,相图变窄.在体系汽液相总组成相同情况下,硬壁狭缝内体系的汽液相密度均比主体相中小;随壁面原子能量参数增大,气相密度变大、液相密度在CH4的摩尔分数较小时变大而当CH4的摩尔分数达到一定值后反而减小.在体系汽液相总组成相同时,受限环境下的汽化热比主体相的汽化热小且随壁面吸引势的增强越来越小;在主体相和硬壁狭缝中体系的汽化热随CH4含量的增加单调减小,而当壁面势能参数较大时汽化热随CH4含量增加先增大后减小.     

Molecular dynamics study of water molecule diffusion in oil-paper insulation materials

Moisture is an important factor that influences the safe operation of transformers. In this study, molecular dynamics was employed to investigate the diffusion behavior of water molecules in the oil-paper insulation materials of transformers. Two oil-cellulose models were built. In the first model, water molecules were initially distributed in oil, and in the second model, water molecules were distributed in cellulose. The non-bonding energies of interaction between water molecules and oil, and between water molecules and cellulose, were calculated by the Dreiding force field. The interaction energy was found to play a dominant role in influencing the equilibrium distribution of water molecules. The radial direction functions of water molecules toward oil and cellulose indicate that the hydrogen bonds between water molecules and cellulose are sufficiently strong to withstand the operating temperature of the transformer. Mean-square displacement analysis of water molecules diffusion suggests that water molecules initially distributed in oil showed anisotropic diffusion; they tended to diffuse toward cellulose. Water molecules initially distributed in cellulose diffused isotropically. This study provides a theoretical contribution for improvements in online monitoring of water in transformers, and for subsequent research on new insulation materials.