Interactions of 1-butyl-3-methylimidazolium hexafluorophosphate with N,N-dimethylformamide: Density and viscosity measurements

Article abstract of DOI:10.1016/j.molliq.2016.03.072

Physico-chemical properties: density (ρ) and viscosity (η) at (303.15, 313.15 and 323.15) K were measured for the binary mixtures of synthesized and characterized ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF₆] with N,N

Full text of DOI:10.1016/j.molliq.2016.03.072

Journal of Molecular Liquids 219 (2016) 661–666
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Interactions of 1-butyl-3-methylimidazolium hexafluorophosphate with
N,N-dimethylformamide: Density and viscosity measurements
a
b
a
a
b,
c,
c
V. Bennett , C.W. Dikio , S.S. Angaye , D. Wankasi , E.D. Dikio ⁎, I. Bahadur ⁎, E.E. Ebenso
a
Department of Chemical Sciences, Niger Delta University, Wilberforce Island, P.M.B, 071 Yenagoa, Bayelsa State, Nigeria
Applied Chemistry and Nanoscience Laboratory, Department of Chemistry, Vaal University of Technology, P. O. Box X021, Vanderbijlpark, South Africa
Department of Chemistry, School of Mathematical and Physical Sciences, Materials Science Innovation & Modelling (MaSIM) Research Focus Area, Faculty of Agriculture, Science and Technology,
b
c
North-West University (Mafikeng Campus), Private Bag X2046, Mmabatho 2735, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
Physico-chemical properties: density (ρ) and viscosity (η) at (303.15, 313.15 and 323.15) K were measured for the
binary mixtures of synthesized and characterized ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate
Received 27 January 2016
Received in revised form 10 March 2016
Accepted 11 March 2016
Available online 18 April 2016
[
6
BMIM][PF ] with N,N-dimethylformamide (DMF) over the entire range of mixture composition. These data have
E
been used to calculate the excess volume (V ), deviations in viscosity (Δη) and excess Gibbs free energy of
E
activation of viscous flow (ΔG* ). These results are fitted to the Redlich-Kister polynomial equation to derive the
binary coefficients and standard deviations. The experimental and calculated quantities are used to study the
nature of the intermolecular interactions between the mixture components. The viscosities were correlated with
single parameter Grunberg and Nissan model, Hind model, Frenkel model and Kendall and Monroe model.
© 2016 Elsevier B.V. All rights reserved.
Keywords:
Thermodynamics
Intermolecular interactions
Ionic liquid
Excess Gibbs free energy
Excess molar volumes
1
. Introduction
thermodynamic excess functions which are usually described to be
either positive or negative. This classification is used to develop statistical
An ionic liquid (IL) is a salt that is liquid below 100 °C [1–7]. ILs is usu-
ally quaternary ammonium salts. Cations such as, tetraalkylammonium
[R N ] or cyclic amines (imidazolium, pyridinium, pyrrolidinium and
4
theories based on fluid models to interpret the deviations from ideal
behaviors of the binary liquid systems. The thermodynamic functions
are used to give a more quantitative understanding of the nature of inter-
molecular interactions of binary liquid systems. Density and viscosity of
liquid mixtures are important in most engineering calculations and
different analytical applications [12]. Hence, evaluation and prediction
of these properties of solvent mixtures as functions of temperature and
composition are of theoretical and practical importance because these
mixtures are used in titration, calorimetry and reaction calorimetry
[13]. In the chemical industry knowledge of the thermodynamic proper-
ties of liquids is essential in the designs involving chemical separation,
heat transfer and fluid flow [14]. Moreover, thermodynamic properties
of binary mixtures containing components capable of undergoing
specific interactions exhibit significant deviations from ideality arising
from differences in molecular size, shape and structural changes. The
characterization of the mixtures through their thermodynamic and
transport properties is important from the fundamental point of view
to understand their molecular interactions as well as in practical
applications [15].
+
Guanidinium) are known. Anions may be based on bromo group,
cyano group, chloro group, hexafluorophosphate group [4]. Soon after
the first reports on the synthesis and applications in organometallic
catalysis of the air stable room temperature ionic liquids (RTIL), 1-n-
butyl-3-methylimidazolium tetrafluoroborate, hexafluorophosphate
and their analogues, in the middle of the 1990s a renaissance of the
rich chemistry of molten salts has begun and continues to flourish [6].
There is then no doubt that research into the use of ILs as solvents,
reagents, catalysts and materials will continue to grow. ILs possesses a
unique array of physico-chemical properties that make them important
candidates for a number of energy related task — specific applications.
High polarity, high viscosity, low vapor pressure, non-flammability, low
combustibility and excellent thermal stability [8–11]. However, mixtures
of ILs have been known to have different properties from the properties
of the pure liquids. In thermodynamics, various intermolecular interac-
tions may take place between the component molecules. The types and
strength of such interactions are most times evaluated through some
An extensive literature survey showed that a limited number of
research studies have been reported on the viscosity of DMF with
[
BMIM][PF
phosphate ionic liquid [BMIM][PF
tional ionic liquids and has been widely used in the fields of separation,
6
] binary mixtures. 1-Butyl-3-methylimidazolium hexafluoro-
⁎
Corresponding authors.
E-mail addresses: ezekield@vut.ac.za (E.D. Dikio), bahadur.indra@gmail.com
6
] is one of the most important tradi-
(
I. Bahadur).
http://dx.doi.org/10.1016/j.molliq.2016.03.072
167-7322/© 2016 Elsevier B.V. All rights reserved.
0

662
V. Bennett et al. / Journal of Molecular Liquids 219 (2016) 661–666
catalysis, synthesis, etc [16–18]. DMF is an aprotic polar solvent that is not
able to self-organize hydrogen bonding [19]. It lacks hydrogen bond, large
dipole moment and high dielectric constant [20]. It is a good donor accep-
tor compound [21]. These properties allow DMF to dissolve both polar
and non-polar liquids and it is used in electrolytic capacitors [22].
Rebelo, et al., 2005 [23] analyzed the volumes of the mixtures of
density and viscosity with the data from literature [40–45] is shown in
Table 1.
2.3. Viscosity measurement
Viscosity measurements were carried out using Anton Paar SVM
3000 Stabinger Viscometer. The viscometer has a dynamic viscosity
range of (0.2–20,000) mPa·s, a kinematic viscosity range of (0.2–
[
C
4
C
1
im][BF
vestigated binary mixtures formed by 1-butyl-3-methylimidazolium
hexafluorophosphate [bmim][PF ] with aromatic compound (benzyl
4 2 4 1 4 6
][NTf ] and [C C im][BF ][PF ]. Yanwei, et al., 2007 [24] in-
2
3
6
20,000) mm /s and a density range of (0.65 to 3) g/cm . The instrument
is equipped with a maximum temperature range of 105 °C and a mini-
mum of 20 °C below ambient. Instrument viscosity reproducibility is
0.35% of measured value and density reproducibility 0.0005 g/cm.
alcohol or benzaldehyde) over the full range of compositions at the
temperature range from 298.15 K to 313.15 K and at atmospheric
pressure. Hui, et al., 2012 [25] studied 1-butyl-3-methylimidazolium
hexafluorophosphate with benzene, acetonitrile, and 1-propanol over
the entire composition at 293.15 to 343.15 K. Wei, et al., 2009 [7]
studied methyl methacrylate (MMA) and 1-butyl-3-methylimidazolium
2.4. Infrared measurement
6
hexafluorophosphate ([BMIM][PF ]) ionic liquid binary system, over
IR spectra of synthesized ionic liquid were recorded using Perkin-
the whole concentration range in the temperature range from (283.15
to 353.15) K. Shruti and Shiddhart 2010 [26] studied 1-Butyl-3-
Elmer Spectrum 400 FT-IR/FT-NIR spectrometer in the range 400–
−
1
4000 cm
.
methylimidazolium hexafluorophosphate [BMIM][PF
glycol) [PEG 200] binary mixture.
This paper is a research of the thermodynamic properties of binary
mixtures containing [BMIM][PF ] and DMF. In this research, [BMIM][PF
6
] + Poly(ethylene
2.5. NMR measurement
1H NMR spectra of the ionic liquid in DMSO were measured using a
Bruker Avariqance 400 NMR spectrometer operating at proton frequen-
cy of 300 MHz 75.48 MHz for 13C proton chemical shifts were recorded
relative to an internal TMS standard.
6
6
]
was synthesized and the experimental measurements of density, viscos-
ity and excess molar volume of their binary mixture were measured at
three different temperatures ranging from (303.15 to 323.15) K. The
density, corresponding viscosity deviation, excess molar volume, and
excess Gibbs free energy of activation of viscous flow, were calculated.
Further the excess Gibbs free energy of activation of viscous flow, and
deviation functions were fitted to the Redlich and Kister type polynomial
to estimate the coefficients and the standard deviations. The viscosities
were correlated with single parameter Grunberg and Nissan model,
Hind model, Frenkel model and Kendall and Monroe model. The present
work is a part of our investigations on physicochemical properties of
binary systems [27–39].
2.6. Thermogravimetric analysis
The thermal behavior of the ionic liquid was investigated using a
Perkin Elmer Simultaneous Thermal Analyzer (STA 6000) under a nitro-
gen environment. The ionic liquid sample was heated in platinum
crucibles with nitrogen gas flow rate of 19.7 ml/min and a gas pressure
of 4.0 bars. The dynamic measurement was made from (30 to 950) °C
with a ramp rate of (30 to 900) °C per minute.
2
. Experimental
2.7. Preparation of 1-Butyl-3-methylimidazolium hexafluorophosphate
[
BMIM][PF
6
]
2
.1. Materials
8
1.89 g (1.0 mol) of 1-methylimidazole, 128.95 g (1.0 mol) of and
DMF was purchased from Acros Organics and used without further
92.0 g (1.0 mol) of potassium hexafluorophosphate in a 500 ml three
necked round bottom flask with a reflux condenser at 80 °C for 12 h.
purification. [BMIM][PF
.2. Density measurement
Density measurement of DMF and synthesized ionic liquid was
6
] was synthesized and characterized.
1
-bromobutane De-ionized water (100 ml) was added and a bi-phase
2
was formed. The immiscible ionic liquid layer was separated from the
water phase with a separating funnel. The ionic liquid was washed
with de-ionized water (2 × 50 ml) until the water phase did not react
carried out with an Anton Paar DMA-4500 M digital densitometer
thermostatted at different temperatures. Two integrated Pt 100
platinum thermometers were used for good precision in temperature
control internally (T ± 0.01 K). The densimeter protocol includes an
automatic correction for the viscosity of the sample. The apparatus is
3
with 0.001 M aqueous silver nitrate (AgNO ). Diethyl ether
(2 × 30 ml) was added to the ionic liquid and separated in a separating
funnel. The ionic liquid was dried in vacuum for 2 h. A colorless liquid
was obtained Yield (86%). The ionic liquid was characterized and by
1
13
H and C NMR FTIR and by TGA.
−
5
3
1H NMR of the ionic liquid sample (300 MHz, DMSO) contains peaks at
precise to within 1.0 × 10 g/cm , and the uncertainty of the measure-
−
4
3
ments was estimated to be better than 1.0 × 10 g/cm . Calibration of
the densimeter was performed at atmospheric pressure using doubly
distilled and degassed water. A comparison of our measurements of
δ: 9.05 (s, 1H-imidazole), 7.77 (s, 1H-imidazole), 7.65 (s, 1H-imidazole),
4.16 (s, N–CH ), 3.8 (s, N–methyl), 1.8 (s, CH ), 1.30 (s, CH ), and 0.92
(t, methyl).13C NMR in Fig. 4.4 (300 MHz, DMSO) δ: 19.2 (qt, CH
), 32.3
3
2
2
3
Table 1
Comparison of experimental densities (ρ) and viscosities (η) with literature values.
Component
T = 303.15 K
T = 313.15 K
T = 323.15 K
3
3
3
ρ (g/cm )
η (mPa·s)
ρ (g/cm )
η (mPa·s)
ρ (g/cm )
η (mPa·s)
[
BMIM][PF
6
]
Experiment
Literature
1.3608
1
187.63
1.3524
1.35430
1.3550
129.67
1.3441
1.34598
1.3468
88.51
74.9
.362404
0
202
42
41
120.0
42
41
42
41
43
42
43
42
1.36286
199.7
120.7
.3631942
1.35419
44
119.0
40
1
4
0
1.354
DMF
Experiment
Literature
0.9387
0.74
0.82
0.9291
0.9307
0.66
0.75
0.9195
–
0.59
–
0.940245
45
45
45

V. Bennett et al. / Journal of Molecular Liquids 219 (2016) 661–666
663
Table 2
E
Mole fraction (x
1
) of DMF, density (ρ), viscosity (η), deviation in viscosities (Δη), molar volume (V
m
), excess molar volume (V ), excess Gibbs free energy of activation of viscous flow
E
(
ΔG* ), Kendall-Monroe (Eηm) and Grunberg-Nissan (d′) parameters for binary mixture of DMF (x
1
) + [BMIM][PF ] (x
6 2
) at (303.15, 313.15 and 323.15) K.
3
VE
E
x
1
ρ (g/cm )
η/mPa·s
Δη/mPa·s
V
(
m
ΔG*
Eηm
(mPa·s)
d′
cm·mol−1)
(cm·mol−1)
(J·mol−1)
T = 303.15 K
0.0000
0.3028
0.4909
0.6262
0.7227
0.7963
0.8543
0.9012
0.9399
0.9724
1.0000
1.3524
1.2892
1.1818
1.1718
1.1282
1.0875
1.0512
1.0186
0.9895
0.9632
0.9387
187.63
52.08
15.21
6.21
3.48
2.42
1.93
1.50
1.21
0.98
0.000
−78.989
−80.718
−64.449
−69.152
−36.463
−26.118
−17.791
−10.85
208.7008
168.8444
144.0856
126.2766
113.5747
103.887
96.25267
90.07941
84.98549
80.70764
77.07477
0.0000
0.7675
7.5704
2.3989
2.1204
1.9361
1.6479
1.2949
0.8715
0.4161
0.0000
0.00000
3.72944
2.21065
0.87728
0.32759
0.49193
1.07465
0.90918
0.70867
0.23568
0.00000
0.0000
16.499
9.6145
4.7554
2.335
1.1391
0.5466
0.2513
0.1046
0.0331
0.0000
0.0000
1.6999
0.5898
−0.0676
−0.3596
−0.2247
0.4193
0.5824
0.8391
0.3645
0.0000
−5.0119
0.0000
0.83
T = T = 313.15 K
0.0000
0.3028
0.4909
0.6262
0.7227
0.7963
0.8543
0.9012
0.9399
0.9724
1.0000
1.3441
1.3066
1.2175
1.1643
1.1017
1.0700
1.0441
1.0079
0.9797
0.9530
0.9291
129.67
28.84
5.03
5.20
3.33
2.12
1.70
1.26
1.05
0.83
0.74
0.000
−617.786
−61.347
−43.735
−33.163
−24.881
−17.829
−12.224
−7.4474
−3.4675
0.0000
209.99
169.98
145.13
127.25
114.50
104.77
97.114
90.917
85.805
81.509
77.863
0.0000
−2.6542
2.0377
2.2456
3.9846
2.7767
1.4433
1.4207
0.9044
0.4784
0.0000
0.0000
1.2366
−4.9696
1.1315
1.4881
0.7745
1.2517
0.5998
0.5583
−0.0729
0.0000
0.000
11.359
6.7555
3.4186
1.7195
0.8609
0.4249
0.2014
0.0867
0.0285
0.0000
0.0000
0.3600
−2.8146
0.1046
0.3739
0.0193
0.6232
0.1963
0.5502
−0.9880
0.0000
T = T = 323.15 K
0.0000
0.3028
0.4909
0.6262
0.7227
0.7963
0.8543
0.9012
0.9399
0.9724
1.0000
1.3358
1.2916
1.2130
1.1554
1.1117
1.0678
1.0279
0.9997
0.9703
0.9450
0.9195
88.51
25.91
8.38
4.46
2.20
1.82
1.51
1.08
0.91
0.77
0.66
0.000
−35.997
−37.005
−29.039
−22.826
−16.738
−11.955
−8.2646
−5.033
211.29
171.13
146.19
128.24
115.44
105.68
97.991
91.771
86.638
82.328
78.668
0.00000
−1.86158
1.516032
2.245696
1.952655
2.078664
2.117521
1.315201
0.901667
0.340922
0.000000
0.0000
2.8443
1.3498
1.6373
−0.4077
0.8889
1.5328
0.4919
0.4950
0.2731
0.0000
0.0000
8.0848
4.900
0.0000
1.2019
0.1828
0.3314
−0.7915
0.0798
0.8731
0.0306
0.3967
0.5453
0.0000
2.5321
1.3016
0.6669
0.3373
0.1641
0.0726
0.0246
0.0000
−2.3176
0.0000
(
q, CH
2
), 35.69, (q, CH
2
), 40.55 (tq, N-methyl), 48.5 (t, N–CH
2
),0.120.3
where x
and M
viscosities of pure component 1 DMF and 2 [BMIM][PF
and η are the density and viscosity of the mixtures.
1
and x
2
are the mole fractions calculated from mass fractions.
(dm, imidazole CH), 122.5 (d, imidazole CH), 135.4 (d, imidazole CH).
M
1
2
are molar masses, ρ
1
and ρ are densities, η and η are the
2
1
2
6
], respectively.
3
. Results and discussion
ρ
m
m
E
The excess Gibbs free energy of activation of viscous flow (ΔG* ) for
To investigate the molecular interaction between DMF and
the mixtures was obtained from Eq. (3).
E
[
6
BMIM][PF ], excess molar volume (V ) and deviation in viscosity, Δη
ꢂ
ꢀ
ꢁꢃ
ꢀ
E
data of the binary mixtures were computed from measured density
and viscosity data using the Eqs. (1) and (2), respectively.
ΔG ¼ RT lnη Vm− x1 lnη V1 þ x2 lnη V2
ð3Þ
m
1
2
where R is the universal gas constant, T is the absolute temperature. V
1
x1M1 þ x2M2
x1M1
ρ1
x2M2
ρ2
E
m
2 m
and V are the molar volumes of component 1 and 2; V was obtained
V
¼
−
−
ð1Þ
ð2Þ
ρ
from Eq. (4). η and η and η are the viscosities of component 1 and
1
2
m
ꢀ
ꢁ
2 and mixture, respectively. The values of density, viscosity, excess
molar volume, deviation in viscosity, excess Gibbs free energy of
Δη ¼ η – x1η þ x2η
m
1
2
Table 3
Coefficients Ai, and standard deviations, σ, obtained for the binary system DMF (x
1 6 2
) + [BMIM][PF ] (x ) at different temperatures for the Redlich-Kister equation.
T/K
A
0
A
1
A
2
A
3
A
4
σ
DMF (x
28.639
7.788
1 6 2
) + [BMIM][PF ] (x )
E
3
−1
V /cm mol
303.15
67.931
−92.232
−31.064
−29.839
−112.61
−7406.0
10.093
12.544
103.158
11.552
−473.124
−77.759
−75.20
−406.763
−13440.0
100.368
−49.364
512.336
6.883
−345.242
−74.082
−49.047
−119.057
−7620.0
72.682
−24.904
373.531
20.104
0.3
0.5
0.2
6.18
4.21
0.2
0.2
0.4
0.6
3
3
13.15
23.15
−22.431
−12.521
−39.194
−1370.0
−85.812
27.322
6.528
Δη/mPa·s
303.15
−314.47
−224.29
−146.199
8.538
−17.845
6.037
3
3
13.15
23.15
ΔG* /(J·mol−1)
E
303.15
3
3
13.15
23.15
−83.426
11.675

664
V. Bennett et al. / Journal of Molecular Liquids 219 (2016) 661–666
Table 4
Fitting parameters with Average Percentage Deviation (APD) for the binary mixtures at
different temperatures.
Temperature
K
Frenkel
Hind
η
12
APD
η
12
APD
303.15
313.15
323.15
65.207
44.588
26.958
8.2527
8.1669
8.018
65.207
44.588
26.958
−7.4291
−5.8805
−4.6577
activation of viscous flow, the Grunberg and Nissan constant (dʹ)
and modified Kendall-Monroe (Eηm) for the system under study are
presented in Table 2.
6
Fig. 2. Differential Thermogravimetric Analysis (DTG) of [BMIM][PF ].
E
E
The values of V , Δη and ΔG* were correlated by a Redlich-Kister
[46] type polynomial Eq. (4).
where η12 is a constant attributed to unlike pair interactions. Its value
was obtained from Eq. (9).
k
X
i−1
X ¼ x1x2
Ai ð1‐2x1Þ
:
ð4Þ
i¼1
η12 ¼ 0:5η þ 0:5η
ð9Þ
1
2
The values of parameter A
the experimental values with the Least Square method and are given in
Table 3.
k
were obtained by fitting the equation to
Grunberg and Nissan, formulated Eq. (10) to determine the molecu-
lar interactions leading to viscosity changes.
The standard deviations σ(X) was calculated from Eq. (5).
0
2
2
lnηm ¼ x1 lnη þ x2 lnη þ 2x1x2d
ð10Þ
1
2
2
3
1
=2
X
ꢀ
ꢁ2
N
X expt−Xcalc
where d′ is an interaction parameter which is a function of the compo-
sition and temperature of the binary liquid systems.
The correlating ability of Eqs. (6), (8), (9) and (10) were tested by
calculating the average percentage deviations (APD) between the
experimental and the calculated viscosities were calculated using (11)
6
i¼1
7
5
σðXÞ ¼ 4
ð5Þ
ðN−kÞ
E
where X is the excess volume (V ), deviation in viscosity (Δη) and
E
excess Gibbs free energy of activation of viscous flow (ΔG* ).The sub-
"
#
scripts expt. and calc. represent the experimental and calculated values
respectively. N and k are the number of experimental data points and
the number of coefficients in the Redlich-Kister, 1948 [46] polynomial
equation.
Kendall and Monroe derived Eq. (6) for analyzing the viscosity of
binary mixtures based on zero adjustable parameter.
X
N
APD ¼ 1
00
ηexpt:−ηcalc:
ηexpt:
ð11Þ
N
i¼1
where ηexpt and ηcalc represent the viscosity of experimental and
calculated data, N is the number of experimental data points. The APD
values for the binary mixtures of DMF with [BMIM][PF
6
] are presented
ꢄ
ꢅ
in Table 4.
3
Eηm ¼ x1x2 x1η11=3 þ x2η2
1=3
ð6Þ
The TGA of the ionic liquid presented in Figs. 1 and 2 shows a single
decomposition step. The decomposition of the as-synthesized ionic
liquid started at 407 °C. This is an indication that the ionic liquid was
thermally stable from (0–407) °C. This result is in line with the result
of Truelove and Mantz [47]. Deviations in viscosity were found to be
positive all through the composition range. The positive values of
viscosity deviation for the binary mixtures investigated suggest that
the viscosities of associates formed between unlike molecules were
relatively less than those of the pure components [48]. Fig. 3 clearly
m
where Eη is a modified Kendall-Monroe equation.
The predictive ability of some selected viscosity models such as the
one parameter model of Frenkel Eq. (7) and hind Eq. (8), apply to the
investigated binary systems.
2
2
lnη ¼ x1 lnη1 þ x2 lnη þ 2x1x2lnη
ð7Þ
ð8Þ
2
12
2
2
ƞ ¼ x1 η x2 η þ 2x1x2η
1
2
12
Fig. 3. Deviation in viscosity, Δη with mole fraction (x
(DMF + [BMIM][PF ]) at (303.15, 313.15 and 323.15) K.
1
) DMF in binary mixture of
Fig. 1. Thermogravimetric analysis (TGA) spectrum of [BMIM][PF
6
].
6

V. Bennett et al. / Journal of Molecular Liquids 219 (2016) 661–666
665
Fig. 6. Plots of modified Kendall and Monroe viscosity correlation Eηm (mPa.s) against
mole fraction (x ) DMF in binary mixture of (DMF + [BMIM][PF ]) at (303.15, 313.15
1 6
and 323.15) K.
E
Fig. 4. Plots of excess molar volume (V ) against mole fraction (x
1
) DMF in binary mixture
of (DMF + [BMIM][PF ]) at (303.15, 313.15 and 323.15) K.
6
shows a deviation in viscosity to increase with increase in temperature.
The plots of excess molar volume against mole fraction at (303.15,
A comparison of experimental thermodynamic data of multicompo-
nent mixtures with that calculated by means of various predictive
methods is very useful from different points of view: (i) it suggests
which model is more appropriate to the characteristics of the system,
(ii) it may indicate which parameters should be improved when the
model involves group contributions and (iii) it may allow the identifica-
tion of some model as a convenient reference for the interpretation of
the deviations observed. The viscosity data have been correlated with
semi-empirical equations of modified Kendall and Monroe, Frenkel,
Hind, and Grunberg-Nissan. Grunberg-Nissan interaction parameters
are both positive and negative while the modified Kendall-Monroe
viscosity correlation data are all positive as seen in Table 2. Plots for
the modified Kendall-Monroe viscosity correlation are presented
in Fig. 6. Plots of modified Kendall-Monroe viscosity correlation at
different temperatures show decrease in viscosity with increase in
temperature. The values of Frenkel and Hind are presented in Table 4.
3
6
13.15 and 323.15) K (DMF + [BMIM][PF ]) are presented in Fig. 4.
Excess parameters associated with a liquid mixture are a quantitative
measure of deviation in the behavior of the liquid mixture from ideality.
These functions are found to be sensitive towards the intermolecular
forces and also on the difference in size and shape of the molecules.
Excess volumes of liquid mixtures reflect the result of different
contributions arising from structural changes undergone by the pure
co-solvent. Positive contributions arise from breakup of interactions
between molecules namely, the rupture of hydrogen bonded chains
E
and the loosening of dipole interactions [49]. The values of V for the
6
mixtures of (DMF + [BMIM][PF ]) are positive all through the entire
E
composition but negative at mole fraction 0.3028. The values of V are
the result of contributions from several opposing effects. Positive excess
volume values observed could be attributed to weak interactions
6
between [BMIM][PF ] and DMF molecules. Negative excess molar
volume can be attributed to strong interactions between unlike
molecules through hydrogen bonding as observed at mole fraction
4. Conclusions
0
.3028. The plots of excess Gibbs free energy of activation of viscous
flow against mole fraction at 303.15, 313.15 and 323.15 K for
DMF + [BMIM][PF ]) are presented in Fig. 5. Excess properties provide
Experimental data of density and viscosity for the mixture of
DMF + [BMIM][PF ]) were measured over the entire range of compo-
6
(
(
6
sitions at atmospheric pressure from (303.15 to 323.15) K, from which
the excess molar volumes, deviation in viscosity and excess Gibbs free
energy of activation of viscous flow were calculated and the Redlich-
Kister polynomial equation was applied successfully for the correlation
of the excess/deviation properties. The estimated coefficients and stan-
dard deviation values were also presented. It was found that density and
viscosity for pure components or mixtures decreased with increasing
temperature and viscosity was more sensitive than density to tempera-
ture or composition change. It was found that all of these calculated
quantities were positive, and the Redlich-Kister fitting curves were
information about the molecular interactions and macroscopic behavior
of fluid mixtures which can be used to test and improve thermodynamic
models for calculating and predicting fluid phase equilibria. The magni-
tude of ΔG* represents the strength of interaction between unlike
molecules [50]. Excess Gibbs free energy of activation of viscous flow
E
E
was found to be positive for all plots. In all plots, ΔG* increased with
increase in temperature. The positive values of excess Gibbs free energy
of activation of viscous flow indicate the presence of specific and strong
interactions in the system under investigation [51]. The excess Gibbs
free energy of activation of viscous flow attains a maximum at mole
fraction 0.7227.
E
asymmetric. Positive V values suggest that the rupturing of hydrogen
bonds and the cleavage of dipole-dipole interactions played a significant
role in the mixing behavior which indicates weak interactions of the
component molecules of the binary system. Positive Δη indicates that
there was a loss of dipolar association between unlike components
because of the size and shape of the mixing components. Positive
E
ΔG* suggests the formation of heterogeneous interaction between
unlike components.
Acknowledgments
The authors acknowledge funding from North-West University
and Department of Science and Technology and the National Research
Foundation (DST/NRF) South Africa grant funded (Grant UID: 92333)
for postdoctoral scholarship of Dr. I. Bahadur.
E
Fig. 5. Plots of excess Gibbs free energy of activation of viscous flow (ΔG* ) against mole
References
fraction (x
23.15) K.
1 6
) DMF in binary mixture of (DMF + [BMIM][PF ]) at (303.15, 313.15 and
3
[1] P. Wasserscheid, K. Wilhem, Angew. Chem. Int. Ed. 39 (21) (2000) 3773–3789.

666
V. Bennett et al. / Journal of Molecular Liquids 219 (2016) 661–666
[
[
[
[
[
[
[
2] T.P. Ngoyi, N.S. Nomathemba, D.E. Dikio, J. Elect. Sci. 6 (2011) 2201–2213. [28] N. Deenadayalu, I. Bahadur, T. Hofman, J. Chem, Eng. Data 55 (2010) 2636–2642.
3] E.D. Dikio, G. Vilazi, T.P. Ngoyi, J. Mol. Liq. 177 (2013) 190–197.
4] Y.S. Fung, D.R. Zhu, J. Elect. Soc. 149 (3) (2002) 319–324.
5] J.S. Wilkes, Green Chem. 4 (2) (2002) 73–80.
6] J.H. Davis, P.A. Fox, Chem. Comm. 11 (2003) 1209–1212.
7] F. Wei, Z. Qing, S. Jian, Z. Suojiang, J. Chem, Eng. Data 54 (2009) 2307–2311.
8] P. Bonhte, A.P. Dias, N. Papageorgiou, K. Kalyanasundaram, M. Grätzel, J. Inorg.
Chem. 35 (5) (1996) 1168–1178.
[29] N. Deenadayalu, I. Bahadur, T. Hofman, J. Chem, Eng. Data 56 (2011) 1682–1686.
[30] I. Bahadur, N. Deenadayalu, J. Soln. Chem. 40 (2011) 1528–1543.
[31] I. Bahadur, N. Deenadayalu, Z. Tywabi, S. Sen, T. Hofman, J. Chem. Thermodyn. 49
(2012) 24–38.
[32] I. Bahadur, N. Deenadayalu, Thermochim. Acta 566 (2013) 77–83.
[33] I. Bahadur, N. Deenadayalu, S. Afr. J. Chem. 66 (2013) 200–206.
[34] V. Govinda, P.M. Reddy, I. Bahadur, P. Attri, P. Venkatesu, P. Venkateswarlu,
Thermochim. Acta 556 (2013) 75–88.
[9] P. Wasserscheid, Chem. Commun. 45 (2001) 1186–1187.
[
[
[
[
10] K.R. Seddon, A. Stark, M.J. Torres, 75th ed., ACS Symposium Series. 819, CRC Press,
[35] S. Singh, M. Aznar, N. Deenadayalu, J. Chem. Thermodyn. 57 (2013) 238–247.
[36] I. Bahadur, T.M. Letcher, S. Singh, G.G. Redhi, P. Venkatesu, D. Ramjugernath, J. Chem.
Thermodyn. 82 (2015) 34–46.
Boston Mass, USA, 1994 34–49.
11] H.T. Evans, in: D.R. Lide (Ed.), CRC Handbook of Chemistry and Physics, 75th ed.CRC
Press, Boston Mass, USA, 1994.
[37] S. Singh, I. Bahadur, G.G. Redhi, D. Ramjugernath, E.E. Ebenso, J. Mol. Liq. 200 (2014)
12] Z. Suojlang, S. Ning, H. Xuezhong, L. Xingmel, Z. Xlangping, China Acad. Sci. Beijing
160–167.
(2006) 10080.
[38] S. Singh, I. Bahadur, G.G. Redhi, E.E. Ebenso, D. Ramjugernath, J. Chem. Thermodyn.
89 (2015) 104–111.
[39] S. Singh, I. Bahadur, G.G. Redhi, E.E. Ebenso, D. Ramjugernath, J. Mol. Liq. 199 (2014)
13] M.M. Abbott, H.C. Vanness, Theory and Problems of Thermodynamics, SI Ed.
McGraw-Hill, Inc., 1976 251–259.
[
[
14] A.R. Mahaja, S.R. Mirgane, Ind. J. Chem. 52A (2013) 624–629.
15] E.D. Dikio, S.M. Nelana, D.A. Isabirye, E.E. Ebenso, Int. J. Electrochem. Sci. 7 (2012)
518–523.
[40] D. Tomida, A. Kumagai, K. Qiao, C. Yokoyama, Int. J. Thermophys. 27 (2006) 39–47.
[41] Y. Huo, S.Q. Xia, P.S. Ma, J. Chem, Eng. Data 52 (2007) 2077–2082.
[42] K.R. Harris, L.A. Woolf, M. Kanakubo, J. Chem, Eng. Data 50 (2005) 1777–1782.
[43] M. Qi, G. Wua, Q. Li, Y. Luo, Radiat. Phys. Chem. 77 (2008) 877–883.
[44] M.T. Zafarani-Moattar, H. Shekaari, J. Chem, Eng. Data 50 (2005) 1694–1699.
[45] Y. Geng, T. Wang, D. Yu, C. Peng, H. Liu, Y. Hu, Chin. J. Chem. Eng. Data 16 (2) (2008)
256–262.
1
1101–11122.
[
[
16] H.W. Zhang, K.L. Hong, J.W. Mays, Poly. Bull. 52 (2004) 9–16.
17] J. Carmichael, D.M. Haddleton, S.A.F. Bon, K.R. Seddon, Chem. Commun. 14 (2000)
1237–1238.
[
[
18] Q. Zhou, L.S. Wang, H.P. Chen, J. Chem, Eng. Data 51 (2006) 905–908.
19] A.M. Abubaker, H.A.E.A. Khaled, S.A. Mohammad, S.A. Abel, J. Chem. Thermodyn. 56
(
2013) 106–113.
[46] O. Redlich, A.T. Kister, Ing. Eng. Chem. 40 (1948) 345–348.
[47] P.C. Trulove, R.A. Mantz, Physicochemical properties of ionic liquids, Ionic Liquids in
Synthesis, John Wiley & Sons, Weinheim, Germany 2003, pp. 103–126.
[48] J. Vila, P. Ginés, J.M. Pico, C. Franjo, E. Jiménez, L.M. Varela, O. Cabeza, Fluid Phase
Equilib 242 (2) (2006) 141–146.
[49] L.J.N. Canongia, T.C. Cordeiro, J.M.S.S. Esperança, H.J.R. Guedes, S. Huq, N. Rebelo L. P.,
K.R. Seddon, J. Phys. Chem. B 109 (2005) 3519–3525.
[50] S. Jareena, Ultrasonic, Volumetric and Viscometric Studies on Binary Mixtures of N-
Alkyl Anilines at Different Temperatures, PhD Thesis, Acharrya Nagarjuna University,
India, 2014.
[
[
[
[
20] P. Venkatesu, Fluid Phase Equilib. 298 (2010) 173–191.
21] Y. Marcus, The Properties of Solvents, John Wiley & Sons, Inc., Netherlands, 1998.
22] R.S. Gopal, D. Agarwal, K. Agarwai, J. Chem. Thermodyn. 8 (1976) 1205–1207.
23] L.P.N. Rebelo, L.J.N. Canongia, T.C. Cordeiro, J.M.S.S. Esperanca, H.J.R. Guedes, S. Huq,
K.R. Seddon, J. Phys, Chem. B 109 (2005) 3519–3525.
24] Z. Yanwei, W. Haijun, D. Kaishen, J. Chem. Thermody. 39 (2) (2007) 291–296.
25] N. Hui, H. MinQiang, M. QingQing, L. YuanHui, Y. DeZhong, H. BuXing, J. Sci, China
Chem. 55 (2012) 1509–1518.
[
[
[
[
26] T. Shruti, P. Shiddhart, Ind. J. Chem. 49A (2010) 731–735.
27] N. Deenadayalu, I. Bahadur, T. Hofman, J. Chem. Thermodyn. 42 (2010) 726–733.
[51] T.M. Reed, T.E. Taylor, J. Phys. Chem. 63 (1959) 55–58.