Translational diffusion of polystyrene in 1,4-dioxane at infinite dilution determined with the extended Taylor dispersion method

The extended Taylor dispersion method was used to determine the translational diffusion coefficients of a series of polystyrene standards in 1,4-dioxane at infinite dilution at temperatures from 323.2 to 378.2 K. The experimental data suggest that in the context of Kirkwood's theory the Monte Carlo chain represents real polystyrene molecules better than does the Guassian chain with physically reasonable values for the hydrodynamic interaction parameter h^*. The feasibility and accuracy of the simultaneous determination of the diffusivities of several polystyrene standards from a single dispersion measurement were also analyzed using a binary mixture of polystyrenes with molecular weights of 2000 and 100,000 as an example.     

环己烷在聚乙烯和聚异丁烯中无限稀释扩散系数 的测定

采用填充柱的反相气相色谱方法,基于Hadj-Romdhane-Danner色谱过程的数学模型,在323.2～363.2K温度范围内测定了环己烷在聚异丁烯和聚乙烯膜中的无限稀释扩散系数。从实验数据可以看出,环己烷更容易在PIB中发生扩散。对实测扩散数据进行了自由体积理论关联,结果表明,采用空穴自由体积替代Vrentas-Duda自由体积理论方程中自由体积项的修正方程能很好地描述溶剂分子扩散系数随温度的变化关系。     

Translational diffusion of relatively short polystyrene chains in cyclohexane. II. An interpretation of hydrodynamic radius with the freely jointed chain model

The translational diffusion coefficients for three relatively short, nearly monodisperse polystyrene chains (with molecular weights 2000, 4000, and 9000) in liquid cyclohexane have been measured up to 523.2 K using the extended Taylor dispersion method. The resultant hydrodynamic radii are successfully interpreted with the freely jointed chain model corrected for the approximations intrinsic to Kirkwood's theory with Stokes' radius as the only adjustable parameter, which is found to decrease with chain length but approach a constant value for long enough chains. The experimentally observed hydrodynamic radii of polystyrene standards with molecular weights 17,500, 50,000 and 100,000 at 308.2 K conform quite well to the values predicted with the approach formulated in this work.     

Halomethanes in tri-n-octylamine and squalane mixtures at infinite dilution

The retention behavior of eight halomethanes and four saturated hydrocarbons was measured in gas chromatographic stationary phases consisting in tri-n-octylamine (TOA), squalane (SQ) and six TOA+SQ mixtures, at 55.0, 58.5, 62.5 and 65.0°C. Equlibrium constants for complex formation were extracted from experimental data by using a lattice model developed by Martire. The results may be interpreted in terms of the formation of weak hydrogen-bonded complexes, with sociation constants of about 0.13 L-mol^–1 for haloforms and 0.07 L-mol^–1 for dihalomethanes at 60°C.     

On the interaction between macroions in solution at infinite dilution

The pair interaction potential for charged macromolecules in solution is calculated from the Ornstein-zernike equation with MSA-closure for the salt-ion/salt-ion and salt-ion/macroion interaction, and HNC-closure for the macroion/macroion interaction. Two different limiting cases are considered: low salt-ion concentration or zero hardcore volume of the macroion. It is found that if the Debye screening length is much larger than the smallest linear dimension of the macroion, the potential is simply a superposition of point-point interaction potentials (screened Coulomb potentials).     

Conformation of biphenyl in a cyclohexane host at 10 K

The site-selected fluorescence, phosphorescence, and luminescence excitation spectra of biphenyl in a cyclohexane Shpol'skii matrix have been measured. There are three principal sites. The relative population of the sites depends on the freezing protocol. The S₁ ↔ S₀ 0&.sbnd;0 band, a forbidden gg transition in D_2h planar biphenyl, is weakly observed for one of the sites. For this site the zero-phonon lines in fluorescence and phosphorescence are accompanied by prominent sidebands but such sidebands are nearly completely absent in the excitation spectrum. The other two sites have negligibly weak 00 bands in fluorescence and minimal sidebands. We attribute the sidebands to translational and/or librational motion of biphenyl in the cyclohexane cage.     

Characterization of thermal diffusion of polystyrene in binary mixtures of THF/dioxane and THF/cyclohexane

The thermal diffusion coefficient (D_τ) was determined for three polystyrene standards of different molecular masses in binary mixtures of tetrahydrofuran/dioxane and tetrahydrofuran/cyclohexane of various compositions. The D_τ values were obtained by combining retention data from thermal field-flow fractionation measurements with diffusion data from dynamic light scattering experiments. In agreement with earlier work of Schimpf and Giddings, the thermal diffusion coefficient was found to be virtually independent of the molecular mass of the polymers. In the binary mixtures of tetrahydrofuran and dioxane, both good solvents for polystyrene, the D_τ value was approximately equal to the average of the D_τ values in the pure solvents, weighted according to the mole fractions of the solvents in the mixture. However, for polystyrene in binary mixtures of tetrahydrofuran and cyclohexane this linear behavior of the thermal diffusion phenomenon was not observed. The addition of cyclohexane to tetrahydrofuran has initially only a minor effect on the molecular and thermal diffusion coefficients of the polystyrene standards. Because cyclohexane is a theta solvent for polystyrene, the preferential solvation of polystyrene by tetrahydrofuran could be an explanation for these results. © 1996 John Wiley & Sons, Inc.     

Vapor–liquid equilibrium prediction at high pressures using activity coefficients at infinite dilution from COSMO-type methods

Predictions of vapor–liquid equilibria at high temperatures and pressures were obtained by applying a modified procedure using the Huron–Vidal mixing rule based on available activity coefficients at infinite dilution and low pressures. These activity coefficients were calculated with so-called conductor-like screening model for real solvents (COSMO-RS) and with a variation of this model, known as segment activity coefficient (COSMO-SAC) model.In this work, the performances of the mixing rule (HVID model) coupled with the SRK equation of state and a reduced UNIQUAC model are presented for six binary systems and a ternary system, whose VLE data are available over a large temperature and pressure range.     

Local structure of solvation of nonpolar chains in nonpolar solvents at infinite dilution

The SSOZ (site-site Ornstein-Zernike) equation is used to study the local structure of solvation of linear nonpolar molecules in nonpolar solvents. The atom-atomic interaction potentials are described by the Lennard-Jones potential. The chain-solvent atom-atomic pair correlation functions are calculated in relation to the chain length (number of atoms), solvent density, and the ratio of the geometrical parameters of solvent and chain atoms. Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 4, pp. 742–749, July–August, 1996. Translated by L. Smolina     

Three-phase equilibrium in solutions of polystyrene homologues in cyclohexane

The equilibrium of three liquid phases in solutions of two polystyrene homologues in cyclohexane has been studied experimentally for different values of the average molecular weights of the two polymer species. The compositions of the phases have been determined in some cases. The variation in the size of the three-phase region with change in the molecular weights is discussed, particularly in connection with the occurrence of a tricritical point. Some qualitative observations of the phase behavior in mixed solvent systems are mentioned.     

Thermodynamic properties at infinite dilution of several solutes in ethers by gas-liquid chromatography

Summary The thermodynamic properties of different solutes at infinite dilution have been determined at 323.15 K. Deviations from ideality are discussed in terms of different contributions. The activity coefficients are compared with the calculated values by the one group contribution method.     

The determination of activity coefficients at infinite dilution using g.l.c. for hydrocarbons in furfural at T=278.15 K and T=298.15 K

The activity coefficients at infinite dilution for some alkanes, cycloalkanes, alkenes, alkynes and benzene in furfural have been determined by g.l.c. at T=278.15 K and T=298.15 K. The volatility of the solvent furfural, although low, was taken into account. The method used is an alternative to the pre-saturation method. The results have been used to predict the potential for furfural as a solvent in separating aromatic compounds from aliphatic compounds and other hydrocarbons using extractive distillation. The excess enthalpies of mixing at infinite dilution have also been calculated.     

Measurement of the infinite dilution diffusion coefficients of small molecule solvents in silicone rubber by inverse gas chromatography

The infinite dilution diffusion coefficients of n-hexane, n-heptane and n-decane in crosslinked silicone rubber with different crosslinking agent concentrations were measured in the temperature range of 348.15 K-368.15 K by inverse gas chromatography. The crosslinked silicone rubber was obtained by dissolving PDMS prepolymer, crosslinking agent and catalyst in n-heptane solvent and characterized by FTIR spectra. The Van Deemter equation was used to determine diffusion coefficients from the variation in chromatographic peak width with carrier gas flow rate. The good linear relation indicated the Van Deemter equation used in this work was reliable. The influences of small molecule solvent, crosslinking agent concentration and temperature on the infinite dilution diffusion coefficient were investigated. The results showed that the infinite dilution diffusion coefficient decreased with an increasing number of CH₂ group in the alkane series. The increase in crosslinking agent concentration resulted in decrease of the infinite dilution diffusion coefficient. The infinite dilution diffusion coefficient increased with the rising of temperature. The interdependence on the infinite dilution diffusion coefficient and temperature accorded with Arrhenius equation well. Diffusion constant and activation energy obtained from the Arrhenius equation provided straight lines with the specific critical volume and crosslinking agent concentration.     

Excess enthalpies of 2-propanol + cyclohexane and 2-propanol + benzene + cyclohexane at 298.15 K

With an isothermal dilution calorimeter excess enthalpies have been determined at 298.15 K for 2-propanol + cyclohexane and 2-propanol + benzene + cyclohexane mixtures. The results are fitted with an associated-solution model. Predicted excess enthalpies for the ternary mixture agree well with the experimental results.     

The influence of the extrapolation method on enthalpies of solution at infinite dilution

Analyses have been performed on solution enthalpy data for KCl and NaCl in water at 298.15 K in the molality range below 1 mol kg^?1. In order to calculate the enthalpy of solution at infinite dilution. ΔH^∞, the available data have been extrapolated using five different methods. The influence of the extrapolation method on ΔH^∞ has been discussed taking into account the discrepancies between the different data sets.     

On attractive interaction of a colloid pair of like charge at infinite dilution

Numerical data on the potential of mean force W(r) at infinite dilution of a highly charged colloid pair embedded in a 1:1 electrolyte are reported. The authors obtain attractive minima (W<0) at short interparticle distance in these potential functions in hypernetted chain (HNC) approximation, as salt concentration is increased. These minima, however, disappear in all system sets studied when a self-consistent Zerah-Hansen (ZH) closure is used. The authors infer that the attractive minima obtained in a HNC closure are spurious and result from the neglect of bridge diagrams in HNC approximation. An expression of bridge function, which the ZH closure in effect incorporates in W(r) to remove attractive minima, is derived in terms of modification of correlation functions. Features of repulsive pair potentials obtained using the ZH closure, their dependence on particle charge and salt concentration, and their agreement with those of the Derajguin-Landau-Verwey-Overbeek theory are investigated.