Measurements and correlation of viscosity and conductivity for the mixtures of ethylammonium nitrate with organic solvents

Article abstract of DOI:10.1016/j.molliq.2010.05.003

Transport physicochemical properties of binary mixtures ionic liquid/organic solvent (IL/OS) were studied. Systematical measurements of viscosities (η) and conductivities (Λ) for the binary mixtures of ethylammonium nitrate (EAN) with different OS, over the whole composition range and at temperature ranging from 273.15 K to 313.15 K, were performed. The variation tendency of viscosities/conductivities with composition of the mixtures was explained through the disruption of molecular solutes to ionic association or aggregation of the ionic liquids and correlation between them is carried out by means of Walden product (W). A semi-empirical equation proposed by Jones and Dole was used to describe the variation of viscosity with salt concentration (C). At low concentration of EAN, molar conductivity follows cube root law predicted by the quasi-lattice model. The two transport processes are well described by Arrhenius type laws from which the activation energies for the viscosity (E_a,η) and conductivity (E_a,Λ) are deduced.

Full text of DOI:10.1016/j.molliq.2010.05.003

Journal of Molecular Liquids 155 (2010) 42–50
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Measurements and correlation of viscosity and conductivity for the mixtures of
ethylammonium nitrate with organic solvents
⁎
Yousra Litaeim, Mahmoud Dhahbi
Laboratoire Eau et Technologies Membranaires, BP 273, 8020 Soliman, Tunisia
a r t i c l e i n f o
a b s t r a c t
Article history:
Transport physicochemical properties of binary mixtures ionic liquid/organic solvent (IL/OS) were studied.
Systematical measurements of viscosities (η) and conductivities (Λ) for the binary mixtures of ethylammonium
nitrate (EAN) with different OS, over the whole composition range and at temperature ranging from 273.15 K to
313.15 K, were performed. The variation tendency of viscosities/conductivities with composition of the mixtures
was explained through the disruption of molecular solutes to ionic association or aggregation of the ionic liquids
and correlation between them is carried out by means of Walden product (W).
Received 27 January 2010
Received in revised form 29 April 2010
Accepted 5 May 2010
Available online 11 May 2010
Keywords:
A semi-empirical equation proposed by Jones and Dole was used to describe the variation of viscosity with salt
concentration (C). At low concentration of EAN, molar conductivity follows cube root law predicted by the quasi-
lattice model. The two transport processes are well described by Arrhenius type laws from which the activation
energies for the viscosity (Ea,η) and conductivity (Ea,Λ) are deduced.
Ethylammonium nitrate
Viscosity
Conductivity
Correlation equation
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
order to reduce this inconvenience, mixing IL with other IL or some OS can
be an effective solution, and some new favourable performances can even
Room temperature ionic liquids (RTILs) as a new class of organic
molten salts have been considered as an alternative of traditional organic
solvents owing to many unique physicochemical properties, such as their
non-flammability, their negligible vapour pressure under ambient
temperature which allows classifying them as green solvents and their
favourable solubility of many polar or non-polar organic and inorganic
compounds. A larger temperature range of liquid state permit larger
applications fields compared to conventional OS [1–4]. In light of their
excellent electrochemical characteristics (high electrical conductivity,
wide electrochemical window, high thermal and chemical stability and
high transport numbers) ionic liquids (ILs) have been used in several
electrochemical devices as electrolytes, essentially at fuel cell, double layer
capacitor, solar cell, electrochemical actuators and lithium batteries [5–7].
The ethylammonium nitrate (EAN) is also an organic molten salt with
protonated cation. It presents many properties like the ability to dissolve
organic or inorganic compounds, a large voltage window (∼2 V) and a
relatively high intrinsic conductance, which allows it to be suitable for
electrochemical analysis and an attractive IL [8].
be gained. Therefore, several current studies have focused on the
physicochemical properties of ILs mixtures [1,10,11].
In this study, transport properties of binary mixtures (OS/EAN) in a
broad concentration range from a very diluted solution (0% of IL) to a neat
ionic liquid (100% of IL) at temperatures ranging from 273.15 K to
313.15 K was reported. The viscosity, the conductivity and the activation
energies are the principal transport properties studied.
The dimethyl carbonates (DMC), a little polar aprotic solvent having a
low constant dielectric (ε=3.12), and the formamide (FA), a strongly
polar protic solvent having a strong dielectric constant (ε=109.5) were
chosen as solvents due to their weak viscosities and their large chemical
applications [12,13].
The variation tendency of viscosities/conductivities with composition
of the mixtures was explained through the disruption of molecular solutes
to ionic association or aggregation of the ILs and correlation between these
two sizes is carried out by means of Walden product. The results were
discussed taking into account several theoretical models proposed in the
literature.
Some common organic or inorganic redox systems have been
investigated in EAN at 25 °C and a scale of standard potentials has been
established by Benhlima et al. [8]. Belieres et al. [9] reported an application
of these IL as electrolyte in fuel cells operating in the temperature range
100–200 °C.
2. Experimental
2.1. Chemicals
Pure ILs are highly viscous and exhibit relatively low conductivities,
which is impediment to progress in these electrochemical applications. In
Ethylammonium nitrate (Fig. 1a) (EAN) used in this study was
prepared according to Evans et al. [14,15]. To an ice-cooled stirred solution
of 25% (W/W) ethylamine in water a nitric acid (3 M) was added so a
slight excess of amine remained. The solvent water was evaporated from a
solution with a rotary evaporatory to reduce its water content below a few
⁎
Corresponding author.
E-mail addresses: mahmoud.dhahbi@certe.rnt.tn, dhahbim@yahoo.fr (M. Dhahbi).
0167-7322/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molliq.2010.05.003

Y. Litaeim, M. Dhahbi / Journal of Molecular Liquids 155 (2010) 42–50
3. Results and discussion
43
3.1. Study of the mixture DMC/EAN
3.1.1. Viscosity
3.1.1.1. Effect of the salt concentration on the viscosity. Knowledge of
electrolyte solutions viscosity is needed for the design of numerous
industrial processes and, at the same time, provides useful insights into
solution structure and interactions [21,22]. In EAN, there are two main
kinds of interactions between molecules: the hydrogen bonds (three-
dimensional hydrogen network similar to the network in water), and
the coulombian interactions which are very strong within an IL
[5,15,23]. From diluted salt solutions of EAN to pure liquid salt short-
range, ion–ion interactions and long range order are confirmed [5,15].
The evolution of dynamic viscosity vs. molar concentration of EAN,
for the binary system (DMC/EAN), over the temperature range from
293.15 K to 313.15 K, was reported in Fig. 2a. At fixed temperature, the
results show an increase in viscosity with increasing salt concentration.
This is due to the fact that with increasing of salt concentration, the
number of collision between the molecules increased resulting in a loss
of kinetic energy. Therefore, the molecules tend to stick together which
increases the viscosity [21].
Fig. 1. Molecular structures of used chemicals.
percentages. Then, the solution was dried in a vacuum desiccator with
phosphorus oxide at room temperature for a few weeks. The water
content for the finally obtained sample ionic liquid was checked to be
negligible below 500 ppm by Karl-Fisher.
1H and 13C NMR spectra were recorded on a Bruker Avance 300
spectrometer. As solvent DMSO (deutero) was used. δH (300 MHz;
DMSO):7.60 (3H, s), 2.88 (2H, quart, J 7.2 Hz), 1.11 (3H, t, J 7.8 Hz); δC
(75 MHz; DMSO): 32.78, 10.14.
This salt is liquid at room temperature and not very viscous. We
checked yet the absence of water by measuring the density of pure salt
and its melting point which is about 14 °C. Its concentration is equal to
11.2 mol L−1
.
Dimethyl carbonate (DMC) (Fig. 1b) and formamide (FA) (Fig. 1c) was
obtained from FLUKA (purityN99%), and were used without further
purification. The binary mixtures (DMC/EAN) or (FA/EAN) were prepared
by volume.
The variation of the viscosity with salt concentration is usually
described by the semi-empirical Eq. (1) initially proposed by Jones and
Dole and subsequently modified by introducing a third term in C2 [24–26]:
pffiffiffi
ηr = η= η0 = 1 + A C + BC + DC2
ð1Þ
2.2. Materials and methods
Density was measured with an Anton Paar digital vibrating tube
densimeter, model DMA 35 N, operating at atmospheric pressure and in
the temperature range from 293.15 K to 313.15 K. The internal calibration
of the instrument was confirmed by measuring the densities of bi-distilled
water, according to the recommendations of the manufacturer. The
Where C is the molar concentration, η and η0 are the viscosities of the
electrolyte solution and the pure solvent respectively. A, B and D are
coefficients which can be calculated (A) or experimentally determined
(B and D).
precision of density measurement was 0.0001×103 kg m−3
.
The ionic A-coefficient is linked to the interaction of the reference ion
with its ionic atmosphere. But, usually the term involving this coefficient
(AC1/2) vanished in organic solvents, when the concentration in salt, is
raised above C≈0.05 M [27,28]. The B-coefficient is related to ion–solvent
interactions as well as to volume effect, the second term (BC) is
predominant at CN0.05 M [29,30]. Very few studies deal with the D
coefficient and its physical meaning is not actually known. It has been
suggested that the intrinsic molar volume of the ions, the ion–solvent
interaction and the ion–ion interactions might contribute to D. The third
term (DC2) appears at highest concentrations in salt more, than 2 M [31].
In order to determine the values of B and D coefficients for different
temperature, a plot of ηr−1 against C was fitted by the method of least
squares.
Various studies have shown that the sign of dB/dT values gives
important information regarding the structure-making and structure-
breaking roles of the solute, in the solvent media, rather than simply the B-
coefficient [32,33]. A perusal of Table 2 shows that the values of the B-
coefficient are positive; which indicates the presence of ion–solvent
interactions. EAN is considered as a structure-breaker for the DMC since
The kinematic (ν) of pure liquid and their binary mixture were
measured with a Micro-Ostwald viscometer from SCHOTT-Instru-
ments, Mainz, which was immersed in a thermostatic water bath
(
0.01 °C). Dynamic viscosities (η) were calculated, using density
and kinematic viscosities values of the respective mixtures. The
accuracy of the viscosity measurements is about 0.01 cP.
The conductivity measurement was carried out on a digital meter
(Metrohm model 712). Besides the measure of the conductivity, the
device allows measuring the temperature ( 0.2 °C), by means of a
sensor Pt 100 and Pt 1000. Thecell constant wascalibratedwith aqueous
KC1 solution. About 50 ml of the mixture was placed in the conductivity
cell which was closed. Circulating water from a thermostatically
regulated bath around the sample holder with double wall was done
to maintain the temperature.
The reliability of experimental measurements of density (ρ), viscos-
ities (η) and conductivity (k) is ascertained by comparing the experi-
mental data of pure liquids with the corresponding values, which were
available in the literature at the studied temperatures (Table 1).
Table 1
Comparison of experimental values of density (ρ), viscosities (η) and conductivity (k) of pure liquids with the corresponding literature values at 298.15 K.
k (mS cm−1
)
η (cP)
ρ (g cm−3
)
Experimental
Literature
Ref
Experimental
29.9
Literature
33
Ref
Experimental
1.22
Literature
Ref
EAN
37.36
35
[16]
[14]
1.21
1.21
0.97
1.13
[7]
(40 °C)
5.2
(40 °C)
5.9
[16]
[17]
[20]
DMC
FA
[17]
[18]
1.16
3.04
0.59
3.32
[17]
[19]
0.93
1.12
1.4.10−7
(20 °C)
2.10−7
(20 °C)

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Y. Litaeim, M. Dhahbi / Journal of Molecular Liquids 155 (2010) 42–50
DMC (10.3 kJ mol−1 [37]). From the same linear regression, contribution
of the salt (Esaa,ηlt) was evaluated to 12.4 kJ mol−1, which is similar to that
found for many tested mixtures OS/IL [1,11].
Table 2
B (M−1) and D (M−2) coefficients of the Jones–Dole equation for the two mixtures
DMC/EAN and FA/EAN.
Solvent
DMC
FA
3.1.2. Conductivity
Coefficient
B
D
B
D
T (°K)
3.1.2.1. Variation of the conductivity with salt concentration. The curves
plotted in Fig. 5a represent the variation of electrical conductivity (k) for
the whole composition range and at different temperatures. It can be seen
that the conductivity of binary mixture increases with the increasing
amount of IL, goes through a maximum and goes down to the specific
conductivity of the neat IL. A maximum of conductivity is located between
6 and 7 mol L−1 and corresponds to a value of 33.25 mS cm−1 at 25 °C.
According to the equation suggested by Every et al. [38], solution
conductivity can be expressed by:
293.15
298.15
303.15
308.15
313.15
0.07
0.13
0.43
0.58
0.67
0.26
0.22
0.16
0.12
0.09
0.12
0.13
0.14
0.15
0.15
0.04
0.03
0.02
0.01
0.00
the values of B increase with increasing temperature (dB/dTN0) [34],
which is a characteristic for dipolar aprotic solvents [35].
3.1.1.2. Effect of the temperature on the viscosity. The viscosities were
found to decrease with increasing temperature (Fig. 2a) due to the rise in
the fluidity of the solution by increasing the kinetic energy of molecules
[21]. The temperature effect on the viscosity of the ionic liquid mixtures
can be fitted by the Arrhenius equation which is a simplified version of
Eyring's absolute rate theory [36]:
k = ∑niqiui
ð4Þ
where ni, qi and ui were respectively, the number of charge carriers of type
i, the charge and the mobility of each species, which is related to the
mixtures viscosities. It can be seen that the increase in the conductivity of a
given system must due to the increase in ion mobility and/or the number
of charge carriers. Several studies [39–43] indicate that there is a
significant ionic association or aggregation in neat ILs, which leads to
the high viscosity, limited conductivity and other peculiar properties, in
these novel materials. Introduction of molecular solutes into ILs will
decrease coulomb interactions in ILs and liberate free ions from their
associates and aggregates, leading to the decreased viscosities and
increased conductivities as a consequence. It is known that solution
fluidity (1/η) is one of the main factors to affect the mobility of charge
carries, so the decrease in viscosity will also lead to the increase of
conductivity.
It is well known, that it is better to analyse the conductometric
properties of electrolytes, in terms of Walden products (W=Λη), because
of the substantial influence of the macroscopic viscosity on ionic mobility
[44]. As shown in Fig. 6a, W falls as temperature and concentration rise,
suggesting that the amount of ionic association increases [45].
To determine the extent of ionic association and to examine the effect
of changing the salt concentration, the curves of molar conductance (Λ)
and viscosity (η) as a function of salt concentration are plotted in the same
graph (Fig. 6b). We note a significant fall in Λ before the viscosity begins to
increase rapidly, suggesting that there is a significant increase in the level
of ionic interaction as the salt concentration raised [45]. The intersection
ꢀ
ꢁ
η = A exp
E
a;n = RT
ð2Þ
where, A, Ea,η, R, and T were respectively, a constant for given mixture, the
activation energy for the viscous flow, the gas constant and the absolute
temperature. Ea,η was evaluated from the plot of Ln(η) vs. (1/T), which is
linear and its slope gives Ea,η value (Fig. 3). The plot of Ea,η against salt
concentration for, a very diluted region (xEAN →0) and the rich salt region
(xEAN →1), were shown in Fig. 4. The activation energy (Ea,η) increases
monotonically according to a linear function. This is due to the fact that at
higher salt concentration, number of ions will be greater that will cause
hindrance in the mobility of ions, which make difficult to produce vacant
sites in the solvate matrix [21]. Furthermore, previous studies [35] were
proposed for a diluted region a linear relation between the activation
energy for the viscous flow and the salt concentration:
Ea;n = Ea-;n + VmEasa;ηltC
ð3Þ
salt
where E°a,η, E
and Vm respectively, are the infinitesimal dilution
a,η
activation energy, the contribution of the salt (per mole of the solute) to
the activation energy for the transport process and the molar volume of
the solvent (84.27 for DMC [13]). The experimental value of the ordinate
at the origin (E°a,η) is 10.38 kJ mol−1 which is close to that for the pure
Fig. 2. Variation of the viscosity with salt concentration at different temperatures for the two mixtures (a) DMC/EAN and (b) FA/EAN.

Y. Litaeim, M. Dhahbi / Journal of Molecular Liquids 155 (2010) 42–50
45
Fig. 3. Verification of the Arrhenius Low for the viscosity of DMC/EAN mixtures.
Fig. 4. Variation of the activation energy for the viscous flow (Ea,η) with the salt concentration for the two systems DMC/EAN and FA/EAN.
Fig. 5. Variations of the conductivity vs. salt concentration at different temperatures for the two systems (a) DMC/EAN and (b) FA/EAN.

46
Y. Litaeim, M. Dhahbi / Journal of Molecular Liquids 155 (2010) 42–50
Fig. 6. (a) Variation of the Walden product with salt concentration for the mixture DMC/EAN. (b) Molar conductivity and viscosity vs. salt concentration at 298.15 K for the mixture
DMC/EAN.
between the two curves confirms the position of maximum conductivity
which was located between 6 and 7 mol L−1
supposed to be dependent on its molar concentration at infinite
dilution [22,35]:
.
Ea;Λ = Ea-;Λ + VmEasa;ΛltC
ð6Þ
3.1.2.2. Effect of the temperature on the conductivity. The conductivities
of EAN, DMC and their mixtures increase as temperature rises (Fig. 5a). At
a fixed concentration, the ions move faster at higher temperature due to
the relatively lower viscosity of the mixture. As the conductance of an ion
depends on its mobility, it is quite reasonable to treat the rate process
taking place with change of temperature on the basis of the Arrhenius
equation [13]:
where E°a,Λ is the activation energy for the conductivity at infinite
dilution, and represented the interactions of one mole of “discharged”
ions (their distance is considered as to large for even long range
interaction to occur). From the plot reported in Fig. 8a, experimental
value of E°a,Λ was equal to 11.86 kJ mol−1 which is alike to many tested
salt
mixtures OS/IL [45]. Salt contribution on the activation energy (E
)
a,Λ
ꢀ
ꢁ
was about 11.74 kJ mol−1
.
Λ = A exp −Ea;Λ = RT
ð5Þ
3.2. Study of the mixture FA/EAN
3.2.1. Viscosity
where A is a constant for a given mixture and Ea,Λ is the activation
energy for the conductivity. From the plot of (Ln Λ) vs. (1/T) which is
linear (Fig. 7), the activation energy (Ea,Λ) values can be evaluated. In
Fig. 8 it was reported the value of Ea,Λ with C from very diluted salt
region (xEAN →0) to rich IL region (xEAN →1). The activation energy
for the ionic conduction process similar to the viscous flow process
increases monotonically with salt concentration. The contribution of
the salt (Esaa,Λlt) to the activation energy (Ea,Λ) for given mixture was
3.2.1.1. Effect of the salt concentration on the viscosity. The evolution of
dynamic viscosity (η) vs. molar concentration (C) of EAN for the binary
system (FA/EAN) over the temperature range considered was reported in
Fig. 2b. Viscosities for the both binary systems follow similar tendencies
except that higher values are registered with the system (FA/EAN).
Fig. 7. Verification of the Arrhenius Low for the conductivity of FA/EAN mixtures.

Y. Litaeim, M. Dhahbi / Journal of Molecular Liquids 155 (2010) 42–50
47
Fig. 8. Variation of the activation energy for the conductivity (Ea,Λ) with the salt concentration for the two systems DMC/EAN and FA/EAN.
Fig. 9. Verification of the Arrhenius Low for the viscosity for FA/EAN mixtures.
Fig. 10. (a) Conductivity as a function of salt concentration at 298.15 K for the two mixtures (DMC/EAN and FA/EAN). (b) Viscosities as a function of salt concentration at 298.15 K for
the two mixtures (DMC/EAN and FA/EAN).

48
Y. Litaeim, M. Dhahbi / Journal of Molecular Liquids 155 (2010) 42–50
Fig. 11. (a) Variation of the Walden product (W) against salt concentration (C) for the mixture FA/EAN. (b) Molar conductivity and viscosity vs. salt concentration at 298.15 K for the
mixture FA/EAN.
Solvation of ions by FA involves mainly electrostatic interactions [46],
although FA molecules are a highly polar (μ=3.37 D at 298.15 K) [47] and
strongly self-associated through extensive three-dimensional network of
hydrogen bonds [47,48]. This may be confirmed by the high values of
viscosity compared to those found for DMC/EAN mixtures. Many
investigations using NMR, IR, Raman spectroscopy, etc. [49–53] have
demonstrated an almost totally ionic structure for formamide in the liquid
state. It can be regarded as a planar molecule with a substantial from a
resonance structure (II).
arrangement of the solvent. A same behaviour was found by R. D. Singh
et al. [54] in the case of tetraalkylammonium ions in solvents of high
dielectric constant.
3.2.1.2. Effect of the temperature on the viscosity. The temperature
dependence of viscosity, for both neat ionic liquids and their mixtures
with FA, in the temperature range of 293.15–313.15 K obeys the
Arrheniuslaw(Eq. (2)). From the slopes of linear regressionsreported in
Fig. 9, experimentalvaluesofactivation energyfor the viscousflow (Ea,η
)
for the hole composition range was evaluated. Fig. 4 showed that Ea,η
values for the FA/EAN mixtures were higher than in the case of the first
mixtures. In fact Ea,η represent necessary energy to the moving particles
for jumping from their initial position to the activate transition state.
This transition led to destroy ion–ion and ion–solvent links [35]. In the
FA/EAN mixtures these links are stronger which proved high energy
values. Ea-;η was about 16.46 kJ mol−1, this value was found by extra-
polation of the curve reported in Fig. 4a. Molar energy (Esaa,ηlt) which
represented in the second term of the Eq. (3) was about 16.17 kJ mol−1
(Vm=39.89 cm3mol−1for FA).
From Table 2, B values for the mixtures FA/EAN vary slightly with
temperature. This indicates that EAN ions do not affect the spatial
Fig. 12. (a) Plot of the molar conductivity Λ vs. the cube root of the concentration C1/3 (C expressed in mol l−1) at different temperatures for the systems (FA/EAN). (b) Activation
energy for conductivity Ea,Λ vs. C4/3 for the system FA/EAN.

Y. Litaeim, M. Dhahbi / Journal of Molecular Liquids 155 (2010) 42–50
49
Fig. 13. Verification of the Arrhenius Low for the conductivity of FA/EAN mixtures.
3.2.2. Conductivity
3.2.2.2. Effect of the temperature on the conductivity. The activation
energy (Ea,Λ) for the whole composition range was evaluated by studying
the variation of the logarithm of the conductivity with 1/T (Fig. 13). The
plot of Ea,Λ against salt concentration (C) (Fig. 8) was linear and obeys to
the Eq. (6). The contribution of the pure solvent to activation energy for
conductivity (Ea°,Λ) and the contribution of the pure salt (Easa,Λlt) were
respectively around, 16.62 kJ mol−1 and 12.75 kJ mol−1. Again energies
values are higher in the case of FA/EAN mixtures, which also were related
to ion–solvent, ion–ion and solvent–solvent interactions.
3.2.2.1. Variation of the conductivity with salt concentration. Fig. 5
shows the variation of electrical conductivity (k) for the whole
composition range and at different temperatures. The same bell shape
was regained which is always a characteristic of LI/OS mixtures [35,45,55],
indicating a competition between the increase in the number of charge
carriers and the decrease in the fluidity, mainly due to the reinforcement
of ion–solvent and ion–ion interactions.
According to the ionic association theory [56,57], the association
constant of an electrolyte decrease with increasing dielectric constant of
the solvent. This is the possible reason why the observed conductivity as
well as the maximum of conductivity increases with the increase of the
dielectric constants of the molecular solvent (Fig. 10a). In the case of FA, a
maximum of conductivity occurs at lower concentrations (between 4 and
5 mol L−1) which can be attributed to the effect of viscosity (Fig. 10b) on
the mobility of charge carriers. In Fig. 11a was represented the variation of
the Walden product vs. molar concentration of EAN at two different
temperatures. It can be noted that increasing in the concentration salt or in
the temperature have no effect on the structure of the solvent. Reporting
the variation of molar conductivity and viscosity in the same graph
(Fig. 11b) proved the position of the maximum conductivity.
From the quasi-lattice theory, a relation between the activation
energy for the conductivity (Ea,Λ) and the salt concentration may be
inferred [22,34]:
Ea;Λ = Ea-;Λ + kC4=3
ð7Þ
where k was constant which dependent on the lattice parameter M,
the number of ions in unit cell of the cation (or anion) pseudo-lattice
and on the molar volume Vm. The variation of Ea,Λ vs. C4/3, reported in
Fig. 12b shows a linear plot as predicted by the theory for an extent
range of concentration until 4M which represented the maximum of
conductivity. Beyond this amount of salt others associated species
than contact ion-pairs affected the quasi-lattice model.
The model of the “pseudo-lattice theory” first introduced by Gosh
[58,59] and developed further by Bahe, [60] allows a precise description of
the variations of the molar conductivity (Λ) for electrolyte solution with C,
which follow the cube root low [61]:
4. Conclusion
The aim of this work was to highlight the transport properties,
viscosity and conductivity, of concentrated organic electrolytes (OS/
IL). The viscosities of the two studied systems (DMC/EAN and FA/
EAN) verified the semi-empirical polynomial Jones–Dole equation
introducing the B parameter. The physical meaning of the B parameter
led to conclude that the presence of EAN destroyed the spatial
arrangement of the DMC but no effect has been noted in the case of FA.
In a limited range of temperature, the viscosity followed an Arrhenius
type law from which the activation energies for viscous flow for the
whole composition range have been deduced. This parameter was a
linear function of the salt concentrations.
Mixtures of EAN with two OS displayed the classical properties of
concentrated saline solutions with a maximum conductivity. Similarly
to the viscosity, molar conductivity followed the Arrhenius law. The
quasi-lattice model, widely used in classical fused salt, has been
successfully extended to concentrated organic electrolytes in partic-
ular for the FA mixtures. Ion–solvent, ion–ion and solvent–solvent
interactions were described by the use of the Walden product.
Λ = Λ0′−S′C1=3
ð4Þ
where Λ0′ and S′ are respectively, the molar conductivity at infinite
dilution and the slope which is mainly dependent on the lattice
parameter value M (equivalent to a Madelung constant).
This interaction model supposed that concentrated electrolyte
solutions are structured media [58,59] and that for 1:1 electrolytes,
the ions were distributed in a face-centred-cubic structure. This
approach considers that the dielectric constant of the medium is
strongly disturbed in the immediate vicinity of the ions, and there are
short-range ion–ion interactions for very concentrated salt solutions.
Fig. 12a proved that molar conductivity for FA/EAN mixtures follows
the cube root low. Similarly, the validity of the suggested relationship
has been tested in aqueous media [62–65] as well as in various
molecular solvent [10,34] with many electrolytes.

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Y. Litaeim, M. Dhahbi / Journal of Molecular Liquids 155 (2010) 42–50
[31] M.M. Lencka, A. Anderko, S.J. Sanders, R.d. Young, Int. J. Thermophys. 19 (1998)
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