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  • 49



    3.1 GENERAL :

    Due to recent developments made in the theories of liquid mixtures and

    experimental techniques, the study of binary liquid mixtures, has attracted several

    researchers in the field [1]. The prediction of the viscosity of liquid mixtures is a

    goal of long standing, with both theoretical and practical importance. A truly

    fundamental theory would predict the viscosity along with other thermodynamic

    and transport properties from the knowledge of the intermolecular forces and

    radial distribution function alone. Such a programme has had appreciable success

    in application to pure simple liquids such as the liquefied rare gases [2], for

    solutions however although the general theory has been formulated, It has not

    been reduced successfully to numerical results.

    One is thus forced to approximate approaches of which two general types

    may distinguished. The first is that of continuous hydrodynamics, whose

    application to molecular problem is identified with names of Einestein and stokes.

    This approach, in which the discrete, molecular nature of solvent is

    neglected, has been remarkably successful in explaining the viscosity o9f dilute

    solutions of high polymers. Its application to solutions in which both components

    are of a comparable size is less appropriate.

    The second general approach is to correlate the viscosity of liquid mixture

    with the properties of pure components and the thermodynamic parameters

    characteristic of the interactions, between components, since viscosity is a

    property of liquid which depends on the intermolecular forces, the structural

    aspects of liquids different concentrations and temperatures.

    Viscosity date and excess thermodynamics functions of binary mixtures

    have been widely used by various workers to know the nature of interactions

    between their components. Relations between viscosity and excess

    thermodynamic functions are also known and these functions can be determined

    from the viscosity data of binary mixtures.

  • 50


    Brown and smith [3] measured volume changes on mixing of benzene

    with methanol, ethanol, 1-propanol, 1-butanol, 2-methyl-2-propanol and hexanol

    by using mixing cell, excess volume values increased with increases in

    temperature and molecular weight of the alcohol.

    Kinematic viscosities and densities were measured [4] experimentally in

    the liquid system acetone-benzene-ethylene dichloride. Viscosities were obtained

    between 25 and 55 oC. and densities between 25 and 45


    Pardo and van Ness [5] determined excess molar volume at 25 and 45oC.

    for binary mixture of ethanol with cyclohexane, toluene, o-xylene p-xylene and

    molar volume were observed.

    Kemal et al. [6] continuing a study of the effect of molecular structure on

    refractive index-density relationships, mixtures of the three possible combinations

    of the aromatics benzene, toluene, and xylene were investigated in the present

    work The effect of composition and temperature on refractive index dispersion

    and density measurement were presented for the mixture of benzene-toluene,

    benzene-xylene and toluene-xylene at 20, 30 and 40 oC. Density measurement

    provided a satisfactory means for analyzing for this system.

    The excess volume of mixing of the binary system benzene-cyclohexane

    were measured [7] as a function of composition at 25 and 40 oC. using a direct,

    dilatometrictechnique. The results were compared with previous determinations,

    and the comparison confirmed the superiority of the direct method of

    measurement over the more usual indirect technique of calculating volume

    changes from density measurements.

    Nigam and Singh [8] determined excess volume for eight binary mixture

    consisting of benzene, toluene, cyclohexane, CCl4 chloroform, bromobenzene and

    chlorobenzene between 35-45 oC. They examined their results in terms of Apm

    and Flory theory. They found Flory theory gave reasonable quantitative

    agreement and correct sign of excess function.

  • 51

    The density viscosity and molecular interaction in binary mixture of

    benzene and toluene with chlorobenzene and bromobenzene were measured [9]

    at 25 to 35 oC. The studies showed the existence of specific interaction between

    the components of the system.

    The densities in air of cycloheptane, n-nonanol, 2- methylcyclohexanol,

    benzaldehyde, chlorobenzene, and bromobenzene were measured [10] from about

    25 to 100 oC. with a modified Robertson pycnometer. The experimental data for

    each compound were fitted to nth degree polynomials in temperature for

    interpolation and limited extrapolation. The agreement with the literature values

    was satisfactory.

    The viscosity of 10 binary systems, including polar and nonpolar

    components, was determined [11] at 20 and 25 oC. The viscosity of the ternary

    system heptane-iso-octanetoluene was also determined at 25 oC. Experimental

    data were correlated by means of the method of McAllister and that of Heric.

    Densities and molar volumes of solutions of nitrobenzene in 18 week

    electron solvents were measured [12] as functions of concentration at 25 oC The

    data were fitted by a least-squares method to a polynomial. No obvious

    relationship was observed between the electron donating ability of the solvents

    and densities of the solutions.

    Densities of mixtures of benzene with four n-alkanes C6, C7, C10 and C16

    were determined [13] at 25 and 50 oC. using a pycnometric method. The density

    measurements were used to extend the corresponding states method of Rowlinson

    and coworkers to systems containing benzene and long chain hydrocarbons.

    Measurements of excess enthalpies in a flow microcalorimeter and of

    excess volumes in a successive dilution dilatometer were carried out [14] at

    298.15 K. For binary mixtures of chlorobenzene with benzene, toluene,

    ethylbenzene, and xylene, m-xylene, and p-xylene.

    The relationship between the composition of the ternary mixtures of

    benzene-toluene-xylene and the refractive index, as well as density, was

    determined [15] at 25 oC.

  • 52

    The viscosities for two systems, nitrobenzene-n-pentane and nitrobenzene-

    n-heptane, were measured [16] for various concentrations and temperatures

    between 20 and 40 oC. The viscosity in the neighborhood of critical point of

    solution became anomalously large. The excess viscosity at the critical point lead

    to a cusp rather than an infinity.

    Ortega et al. [17] determined the excess volume of benzene with several

    isomers of hexanol at 298.15 K. The results were fitted to a polynomial of

    variable degree.

    Rastogi et al. [18] measured excess molar volume for tetrachloro ethylene

    + toluene + p-xylene +CCl4 and + cyclohexane at 303.15 K. For some mixture an

    inversion in sign in excess volume was observed.

    Garrett and Pollock [19] measured the excess volume of benzene and

    toluene with pyridine and methyl pyridine at 298.15 K. A linear correlation

    between Pka and excess volume was found.

    Nath and Singh [20] measured the excess molar volume at 293.15 K. for

    mixture of tetrachloroethylene with benzene, toluene, p-xylene and CCl4. The

    temperature coefficient of excess molar volume was determined.

    Nath and Dubey [21] measured excess molar volume for trichloroethene

    with benzene, toluene, p-xylene, tetrachloro methane and CHCl3 at 303.15 K. by

    using dilatometer.

    The volumes of mixing and dielectric constants of nitrobenzene-sulfolane

    mixtures were measured, [22] at several temperatures ranging within 288.16-

    333.16 K, over the entire composition range. The observed deflations from

    ideality, decreasing with increasing temperature, were interpreted as not

    indicative of significant interactions between unlike molecules.

    Raman et al. [23] measured excess volume of n-alkanol with nitrobenzene

    and chlorobenzene at 303. 15 K. Excess volumes were negative in mixture rich in

    alkanol and positive else were. The results were attributed to the interaction

    between unlike molecules.

  • 53

    Excess volumes of nonelectrolyte solutions of n-heptane, n-octane, and n-

    nonane with chlorobenzene, nitrobenzene and benzonitrile were measured [24] at

    313.5 K. by using a dilatometer.

    Karvo [25] measured the excess enthalpies of sulpholane + benzene,

    toluene, p-xylene and + meistylene at 303.15, 313.15 and 323.15 K. The value

    were positive and increased with increasing hydrocarbon alkylation.

    Viscosities of three binaries, viz., n -hexane-toluene, n -hexane-

    chlorobenzene, and n -hexane-1-hexanol, were determined [26] at 30, 40, 50, and

    60 oC. over the complete composition range. Experimental viscosities were

    compared with values calculated by using equations based on the concept of

    significant liquid structures as well as McAllister type three-body interactions.

    Energies of activation for viscous flow were obtained and their variations with

    composition were discussed.

    Iloukhani et al. [27] measured excess volume of binary mixture of

    substituted benzene with ethyl acetate at 313.15 K. The excess volumes were

    positive over the enti

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