DENSITY AND VISCOSITY STUDIES OF BINARY LIQUID MIXTURES
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 . 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 , 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.
3.2 LITERATURE SURVEY :
Brown and smith  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  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  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.  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  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  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.
The density viscosity and molecular interaction in binary mixture of
benzene and toluene with chlorobenzene and bromobenzene were measured 
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  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
The viscosity of 10 binary systems, including polar and nonpolar
components, was determined  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  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  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  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  at 25 oC.
The viscosities for two systems, nitrobenzene-n-pentane and nitrobenzene-
n-heptane, were measured  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.  determined the excess volume of benzene with several
isomers of hexanol at 298.15 K. The results were fitted to a polynomial of
Rastogi et al.  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  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  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  measured excess molar volume for trichloroethene
with benzene, toluene, p-xylene, tetrachloro methane and CHCl3 at 303.15 K. by
The volumes of mixing and dielectric constants of nitrobenzene-sulfolane
mixtures were measured,  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.  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.
Excess volumes of nonelectrolyte solutions of n-heptane, n-octane, and n-
nonane with chlorobenzene, nitrobenzene and benzonitrile were measured  at
313.5 K. by using a dilatometer.
Karvo  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  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.  measured excess volume of binary mixture of
substituted benzene with ethyl acetate at 313.15 K. The excess volumes were
positive over the enti