Modified free volume theory of self-diffusion and molecular theory of shear viscosity of liquid carbon dioxide

In previous work on the density fluctuation theory of transport coefficients of liquids, it was necessary to use empirical self-diffusion coefficients to calculate the transport coefficients (e.g., shear viscosity of carbon dioxide). In this work, the necessity of empirical input of the self-diffusion coefficients in the calculation of shear viscosity is removed, and the theory is thus made a self-contained molecular theory of transport coefficients of liquids, albeit it contains an empirical parameter in the subcritical regime. The required self-diffusion coefficients of liquid carbon dioxide are calculated by using the modified free volume theory for which the generic van der Waals equation of state and Monte Carlo simulations are combined to accurately compute the mean free volume by means of statistical mechanics. They have been computed as a function of density along four different isotherms and isobars. A Lennard-Jones site-site interaction potential was used to model the molecular carbon dioxide interaction. The density and temperature dependence of the theoretical self-diffusion coefficients are shown to be in excellent agreement with experimental data when the minimum critical free volume is identified with the molecular volume. The self-diffusion coefficients thus computed are then used to compute the density and temperature dependence of the shear viscosity of liquid carbon dioxide by employing the density fluctuation theory formula for shear viscosity as reported in an earlier paper (J. Chem. Phys. 2000, 112, 7118). The theoretical shear viscosity is shown to be robust and yields excellent density and temperature dependence for carbon dioxide. The pair correlation function appearing in the theory has been computed by Monte Carlo simulations.     

Transport properties of CO2-expanded acetonitrile from molecular dynamics simulations

Carbon-dioxide-expanded liquids, which are mixtures of organic liquids and compressed CO2, are novel media used in chemical processing. The authors present a molecular simulation study of the transport properties of liquid mixtures formed by acetonitrile and carbon dioxide, in which the CO2 mole fraction is adjusted by changing the pressure, at a constant temperature of 298 K. They report values of translational diffusion coefficients, rotational correlation times, and shear viscosities of the liquids as function of CO2 mole fraction. The simulation results are in good agreement with the available experimental data for the pure components and provide interesting insights into the largely unknown properties of the mixtures, which are being recognized as important novel materials in chemical operations. We find that the calculated quantities exhibit smooth variation with composition that may be represented by simple model equations. The translational and rotational diffusion rates increase with CO2 mole fraction for both the acetonitrile and carbon dioxide components. The shear viscosity decreases with increasing amount of CO2, varying smoothly between the values of pure acetonitrile and pure carbon dioxide. Our results show that adjusting the amount of CO2 in the mixture allows the variation of transport rates by a factor of 3-4 and liquid viscosity by a factor of 8. Thus, the physical properties of the mixture may be tailored to the desired range by changes in the operating conditions of temperature and pressure.     

Anomalous vibrational energy diffusion in carbon nanotubes

We study the vibrational energy diffusion in single-walled carbon nanotubes by using the molecular-dynamics method. It is found that energy transports ballistically at low temperature and superdiffusively at room temperature. The velocity of energy transport along the axis in carbon nanotube at room temperature is about 0.10 A/fs. It is also found that energy transport in carbon nanotube is different from that one in one-dimensional carbon lattice with the same interaction potential.     

Transport of liquids in barrier plastics

The transport of 1,1,2-trichloroethane, 1,1,2-trichloroethylene, and 1,1,1-trichloroethane in the high nitrile polymer Barex® 210 has been characterized as a function of temperature, polymer moisture content, polymer morphology, film thickness, and composition of liquid mixtures. The characterization studies were conducted using a novel liquid sorption procedure and a new variable temperature liquid permeation instrument. Although the liquids are structurally similar, they exhibit remarkably different transport behavior. 1,1,2-Trichloroethane is a strong penetrant, 1,1,2-trichloroethylene is a weak penetrant, and 1,1,1-trichtoroethane is nearly a non-penetrant for Barex® 210. The results obtained in this study are useful in evaluating transport mechanisms and provide guidance in designing procedures for evaluating barrier plastics as packaging materials for liquid products.     

Influence of Electric Field on Dispersion of Carbon Nanotubes in Liquids

Production processes for carbon nanotubes commonly produce mixtures of solid morphologies that are mechanically entangled or that self‐associate into aggregates. The entangled or aggregated carbon nanotubes often need to be dispersed in corresponding material matrices in order to develop materials that have unique mechanical characteristics or transport properties. The most effective method for dispersion of carbon nanotubes is to prepare fluid suspensions of them in liquid media with applications of surfactant or/and ultrasonication. The authors propose an innovative dispersion method for carbon nanotubes by which an electric field is applied to suspensions of carbon nanotubes in liquids treated by surfactant and ultrasonication. Compared to dispersion without the electric field, the dispersion status of carbon nanotubes in liquid media is evidently improved with the electric field. The results indicate that the electric field conditions are effective for dispersion of carbon nanotubes in liquids and that complex effects of electric field, surfactant, and ultrasonication are beneficial for improvement of dispersion of carbon nanotubes.     

Field dependence of liquid-crystalline phase in liquid-crystal and carbon nanotubes composite

Due to their exceptional properties, liquid crystals are useful for a wide range of applications. As reported in the literature, a slight dispersion of liquid crystals with carbon nanotubes has a detectable effect on the liquid-crystal properties making them appropriate for various applications. The present work reports a new application of these composites disclosing a process of transformation of commercially available high-temperature liquid crystals into low-temperature liquid crystals. This is accomplished by using high concentration of carbon nanotubes in liquid-crystal materials wherein the carbon nanotubes form cluster inside the liquid-crystal cells. The application of bias on these heavily doped samples resulted in the appearance of liquid-crystal phases at room temperature which, in the case of pure liquid crystals, were observable only at high temperature. The process is reversible and hence phase change can be controlled by external field.     

Adsorption and diffusion of carbon dioxide and nitrogen through single-walled carbon nanotube membranes

We have used atomically detailed simulations to examine the adsorption and transport diffusion of CO2 and N2 in single-walled carbon nanotubes at room temperature as a function of nanotube diameter. Linear and spherical models for CO2 are compared, showing that representing this species as spherical has only a slight impact in the computed diffusion coefficients. Our results support previous predictions that transport diffusivities of molecules inside carbon nanotubes are extremely rapid when compared with other porous materials. By examining carbon nanotubes as large as the (40,40) nanotube, we are able to compare the transport rates predicted by our calculations with recent experimental measurements. The predicted transport rates are in reasonable agreement with experimental observations.     

Charge transport properties in carbon black/polymer composites

The charge transport properties of polymer matrix–carbon black composites are investigated in this study. Direct current conductivity is examined with varying parameters: the temperature and the conductive filler content. Conductivity data are analyzed by means of percolation theory, and both percolation threshold and critical exponent are determined at each of the examined temperatures. The temperature dependence of conductivity and the agreement of experimental results with the variable range hopping model reveal hopping conduction as the predominant transport mechanism, below and in the vicinity of the critical concentration of carbon black particles. At higher concentrations, the contribution of hopping transport to the overall conductivity is reduced and a balance between hopping and conduction via geometrical contact occurs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2535–2545, 2007     

Thermal transport coefficients for liquid and glassy water computed from a harmonic aqueous glass

We compute thermal transport coefficients for liquid and glassy water in terms of the vibrations of the quenched liquid. The thermal conductivity and thermal diffusivity are computed for H(2)O and D(2)O at densities from 0.93 to 1.2 g cm(-3). The computed thermal diffusivity of liquid water is in reasonable agreement with measured values and is found to increase with increasing temperature due largely to the thermal accessibility of delocalized librational modes. The influence of structure and density on the thermal conductivity of amorphous ices is investigated. The calculations reveal that density alone is unable to explain the measured thermal conductivity of amorphous ices, particularly low-density amorphous ices, for which the thermal conductivity decreases with increasing temperature near 100 K. To investigate the influence of structure on thermal transport in amorphous ices we have computed the thermal transport coefficients for low-density amorphous ices prepared in two different ways, one formed by quenching the liquid at 0.93 g cm(-3) and the other by distortion of cubic ice at the same density. The computed thermal conductivity of the latter is higher, but the structures of both forms are too disordered for the thermal conductivity to exhibit the unusual variation observed experimentally.     

Carbon tetrachloride-induced crack healing in polycarbonate

Crack healing induced by carbon tetrachloride in polycarbonate has been studied at temperatures in the range of 40–60°C. The carbon tetrachloride treatment reduces the glass transition temperature of polycarbonate. Crack healing is observed because the effective glass transition temperature in polycarbonate is reduced to below the test temperature by the carbon tetrachloride treatment. Two distinctive stages of crack healing are divided based on the recovery of mechanical strength and fractograph. The first stage corresponds to the progressive healing due to the convolution of wetting and self-diffusion, which has a constant crack closure rate. Immediately following the first stage, the second stage, corresponding to the self-diffusion of polymer chain, enhances the quality of healing behavior. The transport of carbon tetrachloride in polycarbonate consists of case I (concentration gradient controlled) and case II (relaxation controlled) behaviors. The direction of case II is opposite to that of case I. The solubility decreases with increasing temperature, but diffusivity and velocity for mass transfer, crack closure rate, and diffusion coefficient for the diffusion front have the opposite trend. The first stage of crack healing is controlled by case II transport. The transport of carbon tetrachloride changes the fracture behavior of polycarbonate from ductile to brittle. A comparison of crack healing in polycarbonate and poly (methyl methacrylate) is made. © 1994 John Wiley & Sons, Inc.     

Centroid molecular dynamics approach to the transport properties of liquid para-hydrogen over the wide temperature range

Fundamental transport properties of liquid para-hydrogen (p-H(2)), i.e., diffusion coefficients, thermal conductivity, shear viscosity, and bulk viscosity, have been evaluated by means of the path integral centroid molecular dynamics (CMD) calculations. These transport properties have been obtained over the wide temperature range, 14-32 K. Calculated values of the diffusion coefficients and the shear viscosity are in good agreement with the experimental values at all the investigated temperatures. Although a relatively large deviation is found for the thermal conductivity, the calculated values are less than three times the amount of the experimental values at any temperature. On the other hand, the classical molecular dynamics has led all the transport properties to much larger deviation. For the bulk viscosity of liquid p-H(2), which was never known from experiments, the present CMD has given a clear temperature dependence. In addition, from the comparison based on the principle of corresponding states, it has been shown that the marked deviation of the transport properties of liquid p-H(2) from the feature which is expected from the molecular parameters is due to the quantum effect.     

Carbon-coated core shell structured copper and nickel nanoparticles synthesized in an ionic liquid

A simple synthetic route to prepare carbon-coated copper or nickel nanoparticles is developed in an ionic liquid under microwave heating. The obtained products are characterized by XRD, UV-spectroscopy, and Raman spectroscopy. The morphologies are studied with the help of TEM, HRSEM, and HRTEM. A bulk transport property for carbon coated nickel is reported in this letter.     

Lattice specific heat of carbon nanotubes

The lattice specific heat in carbon nanotubes is evaluated within the microscopic model proposed by Mahan and Jeon, published in the Physical Review B, in 2004. Phonons are considered for single wall carbon nanotubes in armchair configuration. As expected, low temperature and high temperature regions show different behaviour of specific heat. Carbon nanotubes are also displaying a very interesting lattice transport depending on the tube diameter, with high thermal conductivities for small diameters.     

Generalized Johnson-Nyquist noise: white noise of temperature and pressure at the nanoscale

White noise is expected to show up in both pressure and temperature at the nanoscale if linear transport equations prevail. This prediction is based on the thermodynamic fluctuation theory in analogy to a new derivation of the Johnson-Nyquist voltage noise. The pressure noise in liquid filled nanotubes, and temperature noise in nanoslabs are estimated and experiments are proposed. Measurements might prove useful in the determination of nanoscopic transport coefficients.     

Thermophysical Properties of High Temperature Reacting Mixtures of Carbon and Water in the Range 400–30,000?K and 0.1–10?atm. Part 2: Transport Coefficients

The present contribution is continuation of Part 1: Equilibrium composition and thermodynamic properties. This paper is devoted to the calculation of transport properties of mixtures of water and carbon at high temperature. The transport properties, including electron diffusion coefficient, viscosity, thermal conductivity, and electrical conductivity are obtained by using the Chapman?CEnskog method expanded to the third-order approximation (second-order for viscosity), taking only elastic processes into account. The calculations, which assume local thermodynamic equilibrium, are performed for atmospheric pressure plasmas in the temperature range from 400 to 30,000?K for pressures of 0. 10, 1.0, 3.0, 5.0 and 10.0?atm. with the results obtained are compared to those of previously published studies, and the reasons for discrepancies are analyzed. The results provide reliable reference data for simulation of plasmas in mixtures of carbon and water.     

Effect of antiplasticization on gas sorption and transport. I. Polysulfone

The addition of tricresyl phosphate, N-phenyl-2-naphthylamine, and 4,4′-dichlorodiphenyl sulfone to polysulfone causes changes in thermal and mechanical properties of the glassy mixtures associated with antiplasticization, i.e., reduction in glass transition temperature and increase in stiffness. These changes are also found to be accompanied by reductions in sorption of carbon dioxide and the permeability coefficients for helium, carbon dioxide, and methane at low diluent concentrations with reversal of these trends at higher levels as also occurs for the mechanical properties. Detailed analyses of data for carbon dioxide are given in terms of the dual sorption and mobility models often used for glassy polymers. The mobility for gas transport was found to decrease with diluent addition. The major cause for the decreased sorption is the reduction in glass transition temperature accompanying addition of the diluents. The changes in transport behavior approximately parallel the changes in mechanical behavior. These trends are not even qualitatively correlated with estimates of the excess volume changes associated with addition of the diluents to polysulfone.     

液晶冠醚、碳纳米管、水溶性杯芳烃在分析化学中的应用

综述了液晶冠醚、碳纳米管、水溶性杯芳烃在分析化学中应用的新进展。介绍了液晶冠醚在离子传输、分子识别、色谱分析、LB膜等各方面的应用;讨论了碳纳米管在扫描显微镜探针针尖、气体传感器、化学修饰电极和化学分离与检测方面的应用,以及水溶性杯芳烃在光度法、电化学、色谱分离方面的应用。     

Thermophysical Properties of High-Temperature Reacting Mixtures of Carbon and Water in the Range 400–30,000 K and 0.1–10 atm. Part 1: Equilibrium Composition and Thermodynamic Properties

This paper is devoted to the calculation of the chemical equilibrium composition and thermodynamic properties of reacting mixtures of carbon and water at high temperature. Equilibrium particle concentrations and thermodynamic properties including mass density, molar weight, entropy, enthalpy and specific heat at constant pressure, sonic velocity, and heat capacity ratio are determined by the method of Gibbs free energy minimization, using species data from standard thermodynamic tables. The calculations, which assume local thermodynamic equilibrium, are performed in the temperature range from 400 to 30,000 K for pressures of 0.10, 1.0, 3.0, 5.0 and 10.0 atm. The properties of the reacting mixture are affected by the possible occurrence of solid carbon formation at low temperature, and therefore attention is paid to the influence of the carbon phase transition by comparing the results obtained with and without considering solid carbon formation. The results presented here clarify some basic chemical process and are reliable reference data for use in the simulation of plasmas in reacting carbon and water mixtures together with the need of transport coefficients computation.     

双烯类液体橡胶的研发进展

液体橡胶作为合成橡胶的重要种类,是室温下能流动的橡胶材料。本文介绍了液体橡胶的性能特点及分类,着重阐述了双烯类液体橡胶即液体聚丁二烯橡胶、液体丁腈橡胶、液体异戊橡胶、液体丁苯橡胶和液体氯丁橡胶的结构特征、性能特点及主要用途,并进一步探讨了它们的研发、生产和使用情况。液体橡胶便于实现生产连续化和自动化,且加工方便,顺应时代发展的"低碳"潮流。从产品种类、牌号,应用范围等方面对今后的发展提出了建议。