Bulk Viscosity and the Relation between Transport Coefficients

Abstract

The longitudinal and bulk viscosity of the fluid Argon is calculated using its relation with self diffusion coefficient. This relation was derived by developing the relation between coherent and incoherent scattering functions. The results obtained are compared with recent simulation data of bulk viscosity. A good agreement is achieved for a wide range of temperatures at the triple point density. Our results successfully explain the increase in bulk viscosity with decrease in temperature near the triple point. The validity of the relation between diffusion and longitudinal viscosity is also tested for liquid metals. The results obtained for liquid metals of the longitudinal viscosity, at their melting points, are not found to be in agreement with experimental results. A relation between thermal conductivity and self-diffusion coefficient is proposed.     

Controlled Potential Coulometry Employing a Rotating Disk Electrode

Abstract

The application of a rotating disk working electrode to controlled potential coulometry and the electroreduction of copper(II) at a copper disk electrode are described. The electrode has the advantages of reproducible and calculable mass transfer conditions and electrolysis currents which are relatively free of stirring noise. The evaluation of the diffusion coefficient of the electroactive species from the coulometric current-time curve and the fabrication of the electrolysis cell and electrode are also described.     

Thin‐Layer Spectroelectrochemistry on an Aqueous Microdrop

Here we report a technique to perform thin layer spectroelectrochemistry using an aqueous microdrop. The chemical systems used to demonstrate the aqueous microdrop technique were an absorption based ionic probe [Fe(CN)₆]^3?/4? and an emission based ionic probe [Ru(bpy)₃]^3+/2+. The ability of the technique to perform semi‐infinite linear diffusion spectroelectrochemistry on an aqueous microdrop has been previously demonstrated; in this work we were able to demonstrate spectroelectrochemical behavior consistent with the restricted diffusion in a thin layer cell by reducing the analyte volume and the optical path length. The thin‐layer diffusion behavior was illustrated by substantial reduction in peak‐to‐peak separations of the cyclic voltammograms and the significant decrease in electrolysis time compared to the semi‐infinite linear diffusion behavior.     

Thermodynamic studies of the surface and transport properties in Ag–In and Ag–Sb liquid alloys

The surface tension, surface concentration, viscosity and mutual diffusion co-efficients of the Ag–In and Ag–Sb liquid alloys have been calculated using energetics and derivables from a statistical mechanical framework which recognises the formation of atom clusters of self associates. Our calculations suggest the existence of some form of local order in the systems. Ag–In showed higher tendencies to heterocoordination in the bulk-manifested higher values of mutual diffusion coefficient throughout the concentration range. The viscosity values of Ag–In and Ag–Sb were calculated using the expression reported by Kucharsky which relates the viscosity of a liquid binary alloy to the activity coefficients of the liquid alloy components that are raised to some power m. This exponent m is a fitted parameter. The calculated viscosity values for Ag–Sb had some reasonable agreement with experiment above 0.5 atomic fraction of Sb, using a fitted parameter value of m = 4.5. The fitted parameter value for the viscosity of Ag–In is expected to be in the range 1.5 ≤ m ≤ 3.5.     

Empirical Relationships between Transport Coefficients of Liquid Metals over a Range of Thermodynamic States

Abstract

Assuming the Wiedemann-Franz law, measured data for electrical conductivity α of liquid Cs and Rb is converted to λ_e , the electronic contribution to the thermal conductivity A. While the major part of the measured thermal conduction is thereby accounted for, the “residual” ionic contribution, denned as (^λ-1—λ_e ^?1)^?1, does not simply increase as the metal-insulator transition is approached along the coexistence curve.

Since λ is dominated by _λe, it is surprising that a hard sphere model, which predicts λ/n = 5k_B/2M with n the shear viscosity and M the ionic mass, still gives correctly a relatively constant ratio, though a difference in behaviour of λ/n as a function of thermodynamic state is noted for liquid Rb and Cs compared with liquid argon.

A generalization of Andrade's formula for shear viscosity at the melting point is also discussed, including the work of Zwanzig relating the self-diffusion coefficient D to n via the bulk viscosity.     

Ternary diffusion coefficients of diethanolamine and N-methyldiethanolamine in aqueous solutions containing diethanolamine and N-methyldiethanolamine

Ternary diffusion coefficients of diethanolamine (DEA) and N-methyldiethanolamine (MDEA) in aqueous solutions containing DEA and MDEA using the Taylor dispersion technique have been measured for temperatures (303.2, 313.2, and 323.2 K). The systems studied were aqueous solutions containing total amine concentrations of 2.5 and 4.0 kmol m⁻³, each having four different amine molar ratios. The density and viscosity of the blended amine solutions were also measured. The mutual diffusion coefficients of aqueous DEA and aqueous MDEA solutions were also reported. The main diffusion coefficients (D₁₁ and D₂₂) and the cross-diffusion coefficients (D₁₂ and D₂₁) were reported as function of temperature and concentration of alkanolamines. The limiting conditions for the main diffusion coefficients and the cross-diffusion coefficients were discussed at first, and a comparison between the ratios of the cross-diffusion coefficients to the main diffusion coefficients for DEA and MDEA was made. The dependence of the main diffusion coefficients on the viscosity of solutions was also investigated.     

Nitric Acid-Air Diffusion Coefficient: Experimental Determination Using a Diffusion Cell

Abstract

Trace gaseous nitric acid was generated using a diffusion cell. The determination was made by collection in cellulose filters coated with K₂CO₃ and measuring the concentration by ion chromatography. The measured HNO₃-air diffusion coefficient was 0.0404±0.0010 cm²/s (n=21) for T=298.15 K and P=1 atm. Their dependence with the temperature, over the range from 297.15 K to 318.15 K, could be expressed by D = 10^?4.7773.T^1.366 (R²=0.9467).     

Evaluation of the separation performance of polyvinylpyrrolidone as a virtual stationary phase for chromatographic NMR

Polyvinylpyrrolidone (PVP) was used as a virtual stationary phase to separate p‐xylene, benzyl alcohol, and p‐methylphenol by the chromatographic NMR technique. The effects of concentration and weight‐average molecular weight (Mw) of PVP, solvent viscosity, solvent polarity, and sample temperature on the resolution of these components were investigated. It was found that both higher PVP concentration and higher PVP Mw caused the increase of diffusion resolution for the three components. Moreover, the diffusion resolution did not change at viscosity‐higher solvents. Moreover, the three components showed different resolution at different solvents. As temperature increased, the diffusion resolution between p‐xylene and benzyl alcohol gradually increased, and the one between p‐xylene and p‐methylphenol slightly increased from 278 to 298 K and then decreased above 298 K. It was also found that the polarity of the analytes played an important role for the separation by affecting the diffusion coefficient. Copyright © 2014 John Wiley & Sons, Ltd.     

电解制备二氧化锰强酸性电解液中气体扩散电极的稳定性与失效行为

采用气体扩散电极(GDE)代替传统析氢阴极电解制备二氧化锰(EMD),重点研究了气体扩散电极在强酸性MnSO4-H2SO4电解液中的稳定性、寿命及失效行为.结果表明:气体扩散电极在MnSO4-H2SO4电解液中重现性好、具有一定的稳定性,寿命可达400 h;平行实验表明,阳极沉积一定厚度的EMD是槽电压第一次升高的主要原因;电流密度为100 A m-2时,气体扩散电极失效前阴极过程的速度由氧的离子化反应和氧的扩散混合控制,失效后阴极过程由氧去极化和氢去极化共同组成,主要发生析氢反应;催化层聚四氟乙烯(PTFE)网络结构的破坏和镍网层的溶解是电极失效的原因之一;Pt的团聚降低了电极的电催化活性,是电极失效的主要原因;阴极失效是槽电压再次升高的主要原因.     

Transport properties of separating membranes MF-4SK during alkaline electrolysis of water

The transport properties of separating membranes MF-4SK are studied during electrolysis of H₂O in solutions of KOH. The effective diffusion coefficients of molecules of KOH and H₂O and the transfer coefficients of ions K⁺ and OH^? and molecules of H₂O are measured at KOH concentrations reaching 11 M, currents reaching 0.31 A cm^?2, at ambient temperature and at 80°C. In contact with a KOH solution in the concentration interval 0.1 to 11 M, the membranes that initially swelled in H₂O lose a considerable fraction of water that was present in them and the overall volume of clusters and solution-filled channels in them noticeably decreases. The coefficients of transfer by current of ions K⁺ out of anodic compartment into cathodic and the OH^? ions in the reverse direction, respectively, happen to be equal to about 0.6 and 0.4 at ambient temperature and 0.8 and 0.2 at 80°C. The coefficients of transfer of water molecules out of the anodic volume into the cathodic volume in the process of electrolysis happen to be in the limits 1.6–1.9 at ambient temperature and in the limits 2.2–2.8 at 80°C. The effective diffusion coefficients of molecules of KOH and H₂O at moderate concentrations of KOH (5.6 M) amount to ～2.6 × 10^?7 and 30 × 10^?7 cm²s^?1 at ambient temperature and ～4 × 10^?7 and 61 × 10^?7 cm²s^?1 at 80°C, respectively. At a high concentration of KOH (～10 M) these quantities substantially diminish.     

Chronopotentiometric Study of the Reaction Am (III) + 3e → Am(o) in Molten Licl-KCl Eutectic

Abstract

A chronopotentiometric study of the reaction Am(III) + 3e → Am(O) in molten LiCl-KCL is reported. The diffusion coefficient ^DAm(III) increases from 3.5 to 26.0 10^?6 cm² sec^?1 when the temperature was raised from 400 to 650°C. The mechanism of the diffusion is discussed on the base of the hole theory for molten salts.     

Determination of the Micellar Properties of Triton X-100 by Voltammetry Method

ABSTRACT

The diffusion coefficient of the micelle, the first CMC and the second CMC of Triton X-100 are determined by cyclic voltammetry without any probe. The first CMC and the second CMC of Triton X-100 are 3.1x lO^?1 and 1.3× 10^?1 respectively. The viscosity of the micelle solution, the micellar aggregation number and the micellar size increase but the diffusion coefficient decreases with Triton X-100 concentration increasing. The mechanism of the electrochemical reaction of Triton X-100 at platinum electrode is deduced by measurements of conductivity, pH and cyclic voltammetry.     

Diffusion Mechanism of As‐spun Polyacrylonitrile Fiber in a Dimethyl Sulfoxide‐Water Coagulation Bath

In this paper, the diffusion mechanism of as‐spun PAN fiber was investigated in dimethyl sulfoxide‐water by determining the dynamic compositions of the fibers and the diffusion coefficients of solvent and nonsolvent during coagulation. The diffusion process could be divided into two stages. Results showed that the first stage of the diffusion process was the most important during the whole process, which was fundamental to further study on the formation mechanism. Also, compared with wet spinning, the dry‐jet wet spinning method had the advantage of mild coagulating at a high jet‐stretch. At high concentrations, the diffusion coefficients increased and the ratio of solvent diffusion coefficient to nonsolvent diffusion coefficient decreased; an increasing temperature resulted in the increase of both diffusion coefficients with a decrease in their ratios. To some extent, for the PAN‐DMSO‐water system, the more the ratios D_s*/D_n* tended to 1, the more the cross‐section shapes of as‐spun PAN fiber tended to be circular.     

Isotope Effects in Liquid Metals

Abstract

The areas treated in this article are:

(i) The Haeffner effect; where the light isotope moves towards the anode in all cases so far investigated.

(ii) Self diffusion and mutual diffusion.

(iii) Shear viscosity of pure isotopes of Li⁶ and Li⁷.

In the course of the discussion, the Haeffner effect is shown to be directly related to electrical resistively at the level of the lowest order Born approximation.

Models used for treating isotopic mass effects are then considered; limitations and usefulness being assessed by comparison with experimental data on liquid metals. The marked contrast with low temperature isotope effects is finally commented on.     

Viscosity effects in cobaloxime‐mediated catalytic chain‐transfer polymerization of methacrylates

The effect of bulk viscosity on the cobaloxime‐mediated catalytic chain‐transfer polymerization of methacrylates at 60 °C was investigated by both the addition of high molecular weight poly(methyl methacrylate) to methyl methacrylate polymerization and the dilution of benzyl methacrylate polymerization by toluene. The results indicate that the bulk viscosity is not directly linked to the chain‐transfer activity. The previously measured relationship between chain‐transfer‐rate coefficient and monomer viscosity therefore probably reflects changes at the molecular level. However, the results in this article do not necessarily disprove a diffusion‐controlled reaction rate because cobaloxime diffusion is expected to scale with the monomer friction coefficient rather than bulk viscosity. Considering the published data, to date we are not able to distinguish between a diffusion‐controlled reaction rate or a mechanism directly affected by the methacrylate substituent. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 782–792, 2002; DOI 10.1002/pola.10152     

Titrimetric and Spectrophotometric Determination of Catecholamines

Abstract

Catecholamines can be determined coulometrically at constant-current electrolysis of 30 milliamperes in concentration corresponding to 1×10^?9 to 1×10^?6 equivalents per second of electrolysis time. Iodine - reagent is generated electrically and its amount is evaluated from a knowledge of the current and the generating time. This procedure is compared with the potentiometric method using a redox electrode.     

Rotational and Translational Dynamics of Ras Proteins upon Binding to Model Membrane Systems

Plasma-membrane-associated Ras proteins typically control signal transduction processes. As nanoclustering and membrane viscosity sensing provide plausible signaling mechanisms, determination of the rotational and translational dynamics of membrane-bound Ras isoforms can help to link their dynamic mobility to their function. Herein, by using time-resolved fluorescence anisotropy and correlation spectroscopic measurements, we obtain the rotational-correlation time and the translational diffusion coefficient of lipidated boron-dipyrromethene-labeled Ras, both in bulk Ras and upon membrane binding. The results show that the second lipidation motif of N-Ras triggers dimer formation in bulk solution, whereas K-Ras4B is monomeric. Upon membrane binding, an essentially free rotation of the G-domain is observed, along with a high lateral mobility; the latter is essentially limited by the viscosity of the membrane and by lipid-mediated electrostatic interactions. This high diffusional mobility warrants rapid recognition–binding sequences in the membrane-bound state, thereby facilitating efficient interactions between the Ras proteins and scaffolding or effector proteins. The lipid-like rapid lateral diffusion observed here complies with in vivo data.     

Effect of polymer architecture on self‐diffusion of LC polymers

Two LC side‐group poly(methacrylates) were synthesized, and their melt dynamics were compared with each other and a third, main‐chain side‐group combined LC polymer. A new route was developed for the synthesis of the poly(methacrylate) polymers which readily converts relatively inexpensive perdeuteromethyl methacrylate to other methacrylate monomers. Self‐diffusion data was obtained through the use of forward recoil spectrometry, while modulus and viscosity data were measured using rotational rheometers in oscillatory shear. Diffusion coefficients and complex viscosity were compared to previous experiments on liquid crystal polymers of similar architecture to determine the effect of side‐group interdigitation and chain packing on center of mass movement. The decyl terminated LC side‐group polymer possessed an interdigitated smectic phase and a sharp discontinuity in the self‐diffusion behavior at the clearing transition. In contrast, the self‐diffusion behavior of the methyl terminated LC side‐group polymer, which possessed head‐to‐head side‐group packing, was seemingly unaffected by the smectic–nematic and nematic–isotropic phase transitions. The self‐diffusion coefficients of both polymers were relatively insensitive to the apparent glass transition. The presence of moderately fast sub‐T_g chain motion was supported by rheological measurements that provided further evidence of considerable molecular motion below T_g. The complex phase behavior of the combined main‐chain side‐group polymer heavily influenced both the self‐diffusion and rheological behavior. Differences between the self‐diffusion and viscosity data of the main‐chain side‐group polymer could be interpreted in terms of the defect structure. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 405–414, 1999     

Diffusion of sodium alginate in aqueous solutions at T = 298.15 K

Taylor dispersion technique was used for measuring mutual diffusion coefficients of sodium alginate aqueous solutions at T = 298.15 K, by using as carrier stream solution both pure water and solutions of this polyelectrolyte at a slightly different concentration. The limiting values found at infinitesimal ionic strength, D⁰, were determined by extrapolating to c → 0. These studies were complemented by molecular mechanics calculations. From the experimental data, it was possible to estimate both the limiting conductivity and the tracer diffusion coefficient values for the alginate anion, and the hydrodynamic radius of the sodium alginate (NaC₆H₇O₆), as well as to discuss the influence of the kinetic, thermodynamic and viscosity factors on the diffusion of sodium alginate in aqueous solutions at finite concentrations. Thus, the aim of our innovative research is to contribute to a better understanding of the structure and the thermodynamic behavior of these polymeric systems in solution and supplying the scientific and technological communities with data on these important parameters in solution transport processes.     

Study of Sorption of 2,4‐D on Outer Peristaltic Part of Waste Tire Rubber Granules

From this study it was evident that outer peristaltic parts of waste tire granules gave the highest removal. Film and pore diffusions are the major factors controlling rates of sorption from solution by porous adsorbents. For sorption of 2,4‐D on waste tire rubber granules, the sorption rate coefficient of second‐order kinetic equation was utilized indirectly to determine the rate‐limiting step. The diffusion coefficient lies in the scale of 10^?8 cm²/s, and the pore diffusion coefficient is in the range of 10^?9–10^?10 cm²/s. So both film and pore diffusion are rate limiting. Considering external mass transfer from fluid to particle, using the effect of initial concentration, and using the effect of adsorbent size, no conclusion was reached regarding rate‐controlling steps. It is apparent from the study that external mass transfer (film diffusion) as well as intra‐particle diffusion (pore diffusion) play significant roles in the sorption process for 2,4‐D removal from water onto rubber granules.