Temperature effect on the molecular interactions between two ammonium ionic liquids and dimethylsulfoxide

Article abstract of DOI:10.1016/j.molliq.2011.09.019

To understand the molecular interactions between newly synthesized ammonium ionic liquids (ILs) and highly polar solvent dimethylsulfoxide (DMSO), precise measurements such as densities (ρ), ultrasonic sound velocities (u) and viscosities (η) have been performed over the whole composition range at temperature ranging from 298.15 to 308.15 K and at atmospheric pressure. The ILs investigated in the present study included diethyl ammonium acetate ([Et ₂NH][CH₃COO], DEAA) and triethyl ammonium acetate ([Et₃NH][CH₃COO], TEAA). Further, to gain some insight into the nature of molecular interactions in these mixed solvents, we predicted the excess molar volume (V^E), the deviation in isentropic compressibilities (ΔK_s) and deviation in viscosity (Δη) as a function of the concentration of IL using the measured properties of ρ, u and η, respectively. Redlich-Kister polynomial was used to correlate the results. The intermolecular interactions and structural effects were analyzed on the basis of the measured and the derived properties. A qualitative analysis of the results is discussed in terms of the ion-dipole, ion-pair interactions, and hydrogen bonding between ILs and DMSO molecules and their structural factors.

Full text of DOI:10.1016/j.molliq.2011.09.019

Journal of Molecular Liquids 164 (2011) 218–225
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Temperature effect on the molecular interactions between two ammonium ionic
liquids and dimethylsulfoxide
a
Varadhi Govinda a, Pankaj Attri b, P. Venkatesu b, , P. Venkateswarlu
⁎
a
Department of Chemistry, Sri Venkateswara University, Tirupati - 517 502, India
b
Department of Chemistry, University of Delhi, Delhi - 110 007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 20 July 2011
Received in revised form 21 September 2011
Accepted 26 September 2011
Available online 11 October 2011
To understand the molecular interactions between newly synthesized ammonium ionic liquids (ILs) and
highly polar solvent dimethylsulfoxide (DMSO), precise measurements such as densities (ρ), ultrasonic
sound velocities (u) and viscosities (η) have been performed over the whole composition range at tempera-
ture ranging from 298.15 to 308.15 K and at atmospheric pressure. The ILs investigated in the present study
included diethyl ammonium acetate ([Et2NH][CH3COO], DEAA) and triethyl ammonium acetate ([Et3NH]
[CH3COO], TEAA). Further, to gain some insight into the nature of molecular interactions in these mixed sol-
vents, we predicted the excess molar volume (VE), the deviation in isentropic compressibilities (ΔKs) and
deviation in viscosity (Δη) as a function of the concentration of IL using the measured properties of ρ, u
and η, respectively. Redlich–Kister polynomial was used to correlate the results. The intermolecular interactions
and structural effects were analyzed on the basis of the measured and the derived properties. A qualitative
analysis of the results is discussed in terms of the ion–dipole, ion–pair interactions, and hydrogen bonding
between ILs and DMSO molecules and their structural factors.
Keywords:
DMSO
Ionic liquids
Thermophysical properties
Molecular interactions
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
with no measurable volatility and are able to selectively dissolve differ-
ent types of solute merely by exchanging one of the ions that form the
During the past decade, ionic liquids (ILs), a class of environmen-
tal friendly solvents, have been used for a wide range of industrial
applications. ILs are emerging green solvents and a novel class of liq-
uids mainly due to their special features, such as non-volatility, high
polarizability/dipolarity and their ability to dissolve compounds of
varying polarities. They are simple salts that are liquids below
100 °C or at room-temperature and are entirely composed of different
organic ions [1–7]. They appear to be replacements for noxious vola-
tile organic compounds (VOCs). ILs are also chemically diverse owing
to the huge number of possible cation/anion combinations that can be
synthesized at laboratory level [8]. ILs were initially synthesized in
the early 20th century [9]. To date, there are over 250 types of ILs
prepared, and some of them have been successfully applied in organic
synthesis and other aspects.
Due to the ionic nature of the materials, ILs have essentially negligi-
ble vapor pressure and so can be envisioned as being useful in a variety
of applications [8,10]. The development of ILs as solvents for chemical
synthesis holds a great promise for green chemistry applications [10].
Their perceived status as “designer”, alternative “green” solvents has
contributed largely to the chemical industry, i.e., the existence of fluids
IL, or even more subtly, by altering one of the organic residues within
a given ion. These properties make them very attractive especially in
the emerging field of green chemistry. Therefore, they have become
most promising solvents.
Mixed solvents are almost ubiquitous in the chemical industry in
very different fields ranging from petrochemistry to pharmaceutical
industries. Thermophysical properties of mixed solvents have been
particularly informative in elucidating the solute–solute and solute–
solvent interactions that exist in these solutions. Although a qualita-
tive connection between the macroscopic and microscopic features
is feasible, quantitative conclusions are of interest to both academic
and industrial communities. In spite of importance of properties of
ILs in different solvent media, a small number of thermophysical
data are available in the literature, which mainly characterize ILs
[1–3,11–16]. In this context, in the present manuscript, we have
explored closely three key thermophysical properties such as densities
(ρ), ultrasonic sound velocities (u) and viscosities (η) for the mixed
solvents of ILs and polar solvent at various temperatures.
The highly polar self-associated and aprotic solvent such as
dimethylsulfoxide (DMSO) (μ=4.06 D) [17] was chosen because of
its wide use in applied chemistry and participation in biological pro-
cesses [18,19]. DMSO is a versatile organic liquid having a special sol-
vent power to promote a chemical reaction when used as a reaction
medium. It also exerts a solvent effect sufficient to accelerate a reac-
tion brought about by another reagent. It is also used as a solvent
⁎
Corresponding author. Tel.: +91 11 27666646 142; fax: +91 11 2766 6605.
E-mail addresses: venkatesup@hotmail.com, pvenkatesu@chemistry.du.ac.in
(P. Venkatesu).
0167-7322/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molliq.2011.09.019

V. Govinda et al. / Journal of Molecular Liquids 164 (2011) 218–225
219
for polymerization reactions and displacement reactions because of
its high dielectric constant value (ε=46.45 at 298.15 K) [17]. The
computer molecular dynamics (MD) simulations reveal that in liquid
DMSO, the weak H-bonds C\H⋯O_S are formed [20,21].
2.3.2. Ultrasonic sound velocity measurements
Ultrasonic sound velocities were measured by a single crystal
ultrasonic interferometer (model F-05) from Mittal Enterprises,
New Delhi, India, at 2 MHz frequency at various temperatures. A ther-
mostatically controlled, well-stirred circulated water bath with a
temperature controlled to 0.01 K was used for all the ultrasonic
sound velocity measurements. The uncertainty in sound velocity is
0.02%.
To characterize the type and magnitude of the molecular interac-
tions between DMSO with ILs, we present here the VE, ultrasonic
studies and Δη of DMSO with two ILs, diethyl ammonium acetate
([Et2NH][CH3COO], DEAA) and triethyl ammonium acetate ([Et3NH]
[CH3COO], TEAA) at the temperature ranging from 298.15 to
308.15 K and at atmospheric pressure over the whole composition
range. No effort appears to have been made in literature to study
the molecular interactions between DMSO and these ILs in terms of
VE, ΔKs and Δη. The mixtures of ILs and DMSO provide potential
industrial applications for the utilization of both ILs and DMSO. The
intermolecular interactions and structural effects were analyzed on
the basis of the measured and the derived properties.
2.3.3. Viscosity measurements
Viscosity measurements were performed by using vibro viscome-
ter (Model: SV-10 A&D Company Limited, Japan). The instrument has
been provided with two sensor plates of gold coating. The sample cell
was placed under these sensor plates. Viscosity measurements were
taken from the digital display device attached to the vibro viscometer.
Viscosity measurements of the sample were taken at heating rate
1 K/15 min for getting the thermodynamic equilibrium. A thermo-
2. Experimental
statically controlled, well-stirred circulated water bath with a
temperature controlled to 0.01 K was used for all the viscosity mea-
surements. Typically, the viscosities uncertainty is to be 1%.
2.1. Materials
DMSO (Merck N99% of purity) was stored over freshly activated
3 Å molecular sieves for 48 h and was purified by the standard method
described by Riddick et al. [17]. Acetic acid, diethyl amine and triethyl
amine were purchased from Spectrochem, India. The purity of the
DMSO was verified by measuring the densities (ρ), sound velocity (u)
and viscosity (η) which are in good agreement with literature values
[17,22]. The purity of the sample was further confirmed by GLC single
sharp peaks.
2.3.4. Preparation of samples
Clear solutions were prepared gravimetrically using a Mettler
Toledo balance with a precision of
solution composition expressed in mole fraction was found to be
less than 5×10−4. Mixing of the two components was promoted by
the movement of a small glass sphere (inserted in the vial prior to
the addition of the ILs) as the flask was slowly and repeatedly
inverted. After mixing the sample, the bubble-free homogeneous
sample was transferred into the U-tube of the densimeter, the sample
cell of ultrasonic interferometer or viscometer through a syringe.
0.0001 g. The uncertainty in
2.2. Synthesis of ILs
Both ILs were synthesized in our laboratory [23,24] as given below
and purity of ILs are measured using 1H NMR. 1H (400 MHz) spectra
were recorded on a JEOL 400 NMR spectrometer in DMSO-d6 (with
TMS for 1H as internal references).
3. Results and discussion
To understand the molecular interactions of DMSO with ammoni-
um ILs, we have measured the thermophysical properties such as ρ, u
and η over the whole mole fraction range at temperature ranging
from 298.15 to 308.15 K under atmospheric pressure. Usually, ILs
are miscible with medium- to high-dielectric liquids and immiscible
with low dielectric liquids [25]. In the present study, both ILs are
completely miscible in DMSO (ε=46.45 at 298.15 K) [17], since
DMSO is a high dielectric liquid. Experimental values of ρ, u and η at
various temperatures are reported in Table 1 for ILs, DMSO, and
their mixtures over the whole composition range. The effect of the
ILs on the ρ, u and η in the DMSO has been examined at various tem-
peratures. It was found that the ρ values for the mixtures of DEAA or
TEAA with DMSO decrease as both temperature and concentrations of
the DEAA or TEAA in DMSO increase at all studied temperatures, as
shown in Fig. 1.
2.2.1. Synthesis of diethyl ammonium acetate (DEAA)
The synthesis of ILs was carried out in a 250 mL round bottomed
flask, which was immersed in a water-bath and fitted with a reflux
condenser. Acetic acid (1 mol) was dropped into the diethyl amine
(1 mol) at 343.15 K for 1 h. The reaction mixture was heated at
353.15 K with stirring for 2 h to ensure that the reaction had pro-
ceeded to completion. The reaction mixture was then dried at
353.15 K until the weight of the residue remained constant. The sam-
ple was analyzed by Karl Fisher titration and revealed very low levels
of water (below 70 ppm). The yield of DEAA was 118 g. 1H NMR
(CDCl3): δ (ppm) 1.3 (t, 6H), 1.97 (s, 3H), 2.95 (m, 3H), 9.20 (s, 2H).
2.2.2. Synthesis of triethyl ammonium acetate (TEAA)
Ultrasonic sound velocities are also another important source of
information about the properties of different solvents and their mix-
ture. As it can be seen from Fig. 2, the values of u sharply decrease as
the temperature increases in the ILs with DMSO system. The values of
u were found to increase with increasing the mole fraction of DEAA
and TEAA up to 0.5000 and 0.4000 respectively. At mole fractions
b0.5000 the values sharply increased at all investigated temperatures.
To obtain the mechanism events of the ILs role in the molecular inter-
actions with DMSO, we further studied viscosity measurements for
DEAA or TEAA with DMSO under the same experimental conditions.
From Fig. 3, it is clear that the viscosities increase with increasing
the mole fraction of ILs in DMSO whereas the η values decrease as
the temperature increases in the two systems. It is obvious that the
thermophysical properties reflect the structural properties of liquids
and packing factors of the system. There are no previous ρ, u and η
data reported in the literature for ammonium ILs+DMSO at various
temperatures, for comparison.
A procedure similar to that above for DEAA was followed with the
exception of the use of triethyl amine ([amine]) instead of diethyl
amine. The yield of TEAA was 98%. 1H NMR (CDCl3): δ (ppm) 0.778
(t, 9H), 1.466 (s, 3H), 2.58 (m, 6H), 11.0 (s, 1H).
2.3. Methods
2.3.1. Density measurements
The density measurements were performed with an Anton-Paar
DMA 4500 M vibrating-tube densimeter, equipped with a built-in
solid-state thermostat and a resident program with accuracy of temper-
ature of 0.02 K. Typically, density precisions are 0.00005 g cm−3
.
Proper calibration at each temperature was achieved with doubly
distilled, deionized water and with air as standards. The excess molar
volumes (VE) ( 0.003 cm3 mol−1) were deduced from the densities
of the pure compounds and mixture (ρm) using the standard equations.

220
V. Govinda et al. / Journal of Molecular Liquids 164 (2011) 218–225
Table 1 (continued)
Table 1
Mole fraction (x1) of IL, density (ρ), ultrasonic sound velocity (u), viscosity (η), excess
molar volumes (VE), isentropic compressibility (Ks), and deviation in isentropic com-
pressibility (ΔKs), deviation in viscosity (Δη) for the systems of IL with DMSO at T=
(298.15, 303.15, 308.15) K and at atmospheric pressure.
x1
ρ/
u/
η/
VE/
Ks/
ΔKs/
Δη/
mPa.s
g.cm−3
m.s−1 mPa.s cm3.mol−1 T.Pa−1 T.Pa−1
TEAA with DMSO at 298.15 K
1.09537 1496
0
1.99
2.48
2.72
3.26
3.84
4.42
5.41
6.52
7.81
0
408
399
389
377
364
356
344
332
324
318
315
314
311
309
306
304
302
299
297
295
293
291
0
0
x1
ρ/
u/
η/
VE/
Ks/
ΔKs/
Δη/
mPa.s
0.0236 1.09091 1516
0.0351 1.08886 1536
0.0607 1.08437 1564
0.0879 1.07976 1594
0.1152 1.07550 1616
0.1610 1.06891 1650
0.2116 1.06230 1684
0.2699 1.05553 1710
0.3553 1.04713 1734
0.4353 1.04061 1746
0.4831 1.03730 1754
0.5464 1.03336 1764
0.6163 1.02965 1772
0.6796 1.02673 1784
0.7164 1.02519 1790
0.7846 1.02260 1800
0.8163 1.02149 1808
0.8504 1.02043 1816
0.9064 1.01865 1824
0.9466 1.01738 1832
0.027
0.039
0.071
0.115
0.153
0.214
0.283
0.356
0.435
0.478
0.480
0.473
0.438
0.387
0.350
0.273
0.234
0.180
0.108
0.068
0
−6.3
−15
−0.033
−0.046
−0.074
−0.095
−0.118
−0.143
−0.152
−0.154
−0.143
−0.132
−0.122
−0.112
−0.098
−0.09
−0.084
−0.074
−0.064
−0.058
−0.039
−0.027
0
g.cm−3
m.s−1 mPa.s cm3.mol−1 T.Pa−1 T.Pa−1
−24
−33
−38
−45
−51
−52
−49
−42
−38
−33
−27
−22
−20
−14
−13
−11
DEAA with DMSO at 298.15 K
1.09537 1496
0.0144 1.09397 1500
0.0290 1.0925 1507
0
1.99
2.24
2.53
2.81
3.39
3.98
4.91
5.81
6.74
0
408
406
403
401
397
393
388
383
379
377
376
376
377
378
379
379
380
380
380
379
379
378
0
0
−0.032
−0.060
−0.081
−0.123
−0.16
−0.192
−0.208
−0.206
−0.19
−0.164
−0.126
−0.091
−0.081
−0.067
−0.059
−0.051
−0.041
−0.031
−0.019
−0.008
0
−1.4
−3.8
−6.1
−8.7
0.044
0.123
0.187
0.319
0.442
0.630
0.732
0.803
0.834
0.815
0.720
0.518
0.431
0.344
0.283
0.217
0.136
0.097
0.042
0.013
0
0.0440 1.09091 1513
0.0752 1.08771 1522
0.1077 1.08443 1532
0.1594 1.07915 1546
0.2149 1.07365 1560
0.2747 1.06795 1572
0.3400 1.06204 1580
0.4103 1.05611 1587
0.5136 1.04826 1593
0.6299 1.04053 1595
0.6756 1.03779 1596
0.7186 1.03529 1597
0.7542 1.03333 1597
0.7977 1.03104 1598
0.8465 1.02858 1599
0.8868 1.02662 1601
0.9373 1.02427 1604
0.9747 1.02257 1606
9.71
−12
11.49
12.56
13.97
15.53
16.94
17.76
19.28
19.99
20.75
22.01
22.91
24.12
−16
−19
−21
−21
−20
−17
−12
7.71
8.70
10.09
11.56
12.13
12.66
13.11
13.67
14.29
14.83
15.50
16.01
16.36
−9.7
−8.0
−6.4
−4.8
−2.9
−1.9
−1.0
−0.24
0
−6.6
−4.2
1
1.01586 1840
0
TEAA with DMSO at 303.15 K
1.09241 1472
0
1.79
2.20
2.39
2.82
3.29
3.76
4.55
5.44
6.48
0
422
412
402
389
375
366
353
343
335
327
324
322
320
316
313
311
308
307
304
302
300
298
0
0
0.0236 1.08785 1494
0.0351 1.08569 1514
0.0607 1.08111 1542
0.0879 1.07654 1574
0.1152 1.07207 1596
0.1610 1.06526 1630
0.2116 1.05844 1660
0.2699 1.05128 1686
0.3553 1.04255 1712
0.4353 1.03571 1726
0.4831 1.03221 1734
0.5464 1.02812 1744
0.6163 1.02429 1758
0.6796 1.02123 1768
0.7164 1.01964 1776
0.7846 1.01692 1788
0.8163 1.01578 1792
0.8504 1.01465 1800
0.9064 1.01264 1808
0.9466 1.01138 1816
0.021
0.035
0.061
0.089
0.129
0.186
0.251
0.334
0.411
0.458
0.465
0.456
0.412
0.359
0.320
0.239
0.196
0.142
0.090
0.037
0
−7.7
−16
−0.022
−0.035
−0.063
−0.078
−0.094
−0.123
−0.134
−0.136
−0.129
−0.115
−0.109
−0.098
−0.084
−0.074
−0.071
−0.058
−0.052
−0.040
−0.031
−0.017
0
1
1.02146 1608
−26
−37
−42
−49
−52
−53
−50
−43
−40
−35
−29
−24
−22
−16
−14
−12
DEAA with DMSO at 303.15 K
1.09241 1472
0
1.79
2.04
2.32
2.61
3.13
3.67
4.41
5.17
5.92
6.72
7.51
8.64
9.82
10.28
10.73
11.10
11.54
12.02
12.44
12.96
13.36
13.64
0
422
420
416
413
410
404
399
394
389
386
385
383
382
382
383
383
383
384
384
383
383
382
0
0
0.0144 1.09103 1478
0.0290 1.08949 1485
0.0440 1.08791 1491
0.0752 1.08475 1500
0.1077 1.08129 1512
0.1594 1.07591 1526
0.2149 1.07019 1540
0.2747 1.06427 1554
0.3400 1.05815 1564
0.4103 1.05209 1572
0.5136 1.04405 1582
0.6299 1.03612 1590
0.6756 1.03331 1591
0.7186 1.03077 1592
0.7542 1.02877 1593
0.7977 1.02644 1594
−0.037
−0.065
−0.09
−2.3
−5.2
−7.3
−9.7
0.080
0.186
0.298
0.449
0.604
0.732
0.834
0.875
0.900
0.858
0.764
0.565
0.484
0.425
0.373
0.297
0.199
0.141
0.063
0.019
0
−0.143
−0.176
−0.212
−0.224
−0.218
−0.197
−0.172
−0.135
−0.099
−0.089
−0.078
−0.071
−0.065
−0.052
−0.045
−0.027
−0.017
0
8.01
9.45
−14
−17
−20
−22
−22
−21
−19
−15
−13
−11
−9
10.31
11.45
12.71
13.85
14.51
15.74
16.31
16.93
17.94
18.67
19.64
−7.4
−4.6
−7
−4.6
−3.4
−1.5
−0.53
0
1
1.00958 1824
0
0.8465 1.0239
0.8868 1.0219
1595
1597
TEAA with DMSO at 308.15 K
1.08608 1460
0.9373 1.01946 1599
0.9747 1.01773 1602
0
1.65
1.98
2.13
2.48
2.86
3.24
3.89
4.61
5.45
6.69
7.86
8.56
9.49
10.51
11.44
11.98
12.98
13.44
13.94
14.76
15.35
16.13
0
432
420
410
397
382
372
359
350
341
335
331
328
326
323
320
317
315
314
313
312
311
309
0
0
0.0236 1.08162 1484
0.0351 1.07944 1504
0.0607 1.07492 1530
0.0879 1.07034 1564
0.1152 1.06586 1588
0.1610 1.05908 1622
0.2116 1.05208 1648
0.2699 1.04508 1674
0.3553 1.03615 1698
0.4353 1.02926 1712
0.4831 1.02566 1724
0.5464 1.02154 1732
0.6163 1.01766 1744
0.6796 1.01461 1754
0.7164 1.01300 1764
0.7846 1.01026 1772
0.8163 1.00909 1776
0.8504 1.00784 1780
0.9064 1.00585 1786
0.9466 1.00451 1792
0.012
0.026
0.045
0.071
0.109
0.159
0.234
0.297
0.386
0.431
0.445
0.434
0.391
0.332
0.291
0.208
0.165
0.126
0.068
0.024
0
−8.1
−18
−0.012
−0.028
−0.049
−0.063
−0.077
−0.091
−0.104
−0.109
−0.105
−0.093
−0.086
−0.072
−0.064
−0.051
−0.044
−0.031
−0.030
−0.023
−0.015
−0.006
0
1
1.01652 1604
−27
−39
−46
−53
−57
−57
−53
−47
−44
−38
−33
−28
−26
−20
−17
−14
DEAA with DMSO at 308.15 K
1.08608 1460
0
1.65
1.90
2.18
2.48
2.95
3.45
4.11
4.77
5.40
6.08
6.74
7.69
8.70
9.10
9.46
9.76
10.14
10.52
10.86
11.27
11.6
11.83
0
432
427
425
422
418
412
407
402
396
393
392
388
387
387
387
387
388
388
388
388
388
387
0
0
0.0144 1.08482 1469
0.0290 1.08333 1474
0.0440 1.08187 1480
0.0752 1.07892 1490
0.1077 1.07555 1502
0.1594 1.07029 1516
0.2149 1.06471 1530
0.2747 1.05884 1544
0.3400 1.05285 1554
−0.043
−0.071
−0.101
−0.164
−0.198
−0.235
−0.248
−0.236
−0.216
−0.191
−0.151
−0.113
−0.105
−0.094
−0.087
−0.077
−0.070
−0.063
−0.049
−0.028
0
−4.2
−5.8
−7.9
0.104
0.234
0.382
0.534
0.704
0.838
0.932
0.954
0.968
0.914
0.812
0.637
0.572
0.495
0.432
0.369
0.253
0.182
0.079
0.027
0
−11
−15
−18
−21
−23
−23
−22
−20
−16
−14
−12
−10
0.4103 1.0469
0.5136 1.03899 1574
0.6299 1.0312 1582
1562
0.6756 1.02846 1584
0.7186 1.02597 1586
0.7542 1.02402 1588
−7.7
−5.1
0.7977 1.0217
0.8465 1.01925 1590
0.8868 1.0173 1592
1589
−8.1
1
1.00261 1798
0
−5.4
−3.8
−1.6
−0.79
0
0.9373 1.01492 1594
0.9747 1.01315 1594
The extent of deviation of liquid mixtures from ideal behavior is
best expressed by excess functions. Among them, the excess volumes
can be interpreted in three areas, namely physical, chemical, and
1
1.01187 1599

V. Govinda et al. / Journal of Molecular Liquids 164 (2011) 218–225
221
a
a
1620
1.10
1.09
1.08
1.07
1.06
1.05
1.04
1.03
1.02
1.01
1590
1560
1530
1500
1470
1440
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
x
1
x
1
b
b
1.14
1850
1800
1750
1700
1650
1600
1550
1500
1450
1.12
1.10
1.08
1.06
1.04
1.02
1.00
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
x
1
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
x
Fig. 1. Densities for the mixtures of ILs with DMSO vs. mole fraction of IL x1 for (a) DEAA
{(x1) 298.15 K (○) +, or (x1) 303.15 K (△) +, or (x1) 308.15 K (□)+DMSO (x2)},
(b) TEAA {(x1) 298.15 K (○) +, or (x1) 303.15 K (△) +, or (x1) 308.15 K (□) +, DMSO
(x2)}, at various compositions and atmospheric pressures. The solid line represents the
smoothness of these data.
1
Fig. 2. Ultrasonic sound velocities for the mixtures of ILs with DMSO vs. mole fraction of
IL x1 for (a) DEAA {(x1) 298.15 K (○) +, or (x1) 303.15 K (△) +, or (x1) 308.15 K (□)+
DMSO (x2)}, (b) TEAA {(x1) 298.15 K (○) +, or (x1) 303.15 K (△) +, or (x1) 308.15 K
(□)+DMSO (x2)}, at various compositions and atmospheric pressures. The solid line
represents the smoothness of these data.
structural effects [1–3]. The excess volumes were determined from
the densities of pure compounds (ρ1 and ρ2) and of mixture (ρm)
using the following equation:
Deviations in isentropic compressibility (ΔKs) were evaluated
using the following relation.
VE ¼ Vm−ðx1V1 þ x2V2Þ
ð1Þ
ΔKs ¼ Ks−x1Ks1−x2Ks2
ð4Þ
or
where Ks1, and Ks2 are the isentropic compressibilities of the pure
components 1 and 2, respectively. The deviations in viscosity (Δη)
were calculated by the following equation.
ꢀ
ꢁ
x1M1 þ x2M2
x1M1 x2M2
VE
¼
−
þ
ρ1 ρ2
ð2Þ
ρm
where Vm, V1 and V2 are molar volumes of the mixture and pure com-
ponents; M1, M2 and x1, x2 are the molar masses and mole fractions of
ILs and DMSO, respectively. In recent years, the ultrasonic studies
have been adequately employed in understanding the nature of mo-
lecular interaction in solvent mixed systems. Isentropic compressibil-
ities (Ks) of the binary mixtures were calculated using the relation
from sound velocity (u) and density (ρ);
N
Δη ¼ η−
x η
ð5Þ
∑
i
i
i¼1
where η and ηi denote the viscosity of the mixture and the pure
component, respectively.
The composition dependence of the VE, ΔKs and Δη properties
represents the deviation from ideal behavior of the mixtures and
provides an indication of the interactions between IL and DMSO.
Ks ¼ u−2ρ−1
:
ð3Þ

222
V. Govinda et al. / Journal of Molecular Liquids 164 (2011) 218–225
Table 2
a
18
16
14
12
10
8
Estimated parameters of Eq. (6) and standard deviation, σ for the systems of ILs with
DMSO at various temperatures.
Y
Systems T/K
a0
a1
a2
σ
VE/cm3 mol−1 DEAA
298.15
−0.4838
−0.4666
−0.4871
1.9146 −0.0213
1.8657 −0.1575
1.7747 −0.1238
−73.832
−76.837
−66.989
0.7511
0.7961
0.8779
−0.9841 0.004
−1.2930 0.007
−1.5653 0.010
−0.8072 0.006
−1.2415 0.003
−1.4718 0.002
+DMSO 303.15
308.15
TEAA
298.15
+DMSO 303.15
308.15
DEAA
ΔKs/T.Pa−1
298.15
64.310
70.138
87.562
168.21
185.51
168.77
−9.428
0.8
0.8
2.8
3.0
3.0
2.2
+DMSO 303.15
308.15
TEAA
−18.253
−72.990
−71.42
6
298.15 −163.43
+DMSO 303.15 −167.71
308.15 −191.30
DEAA
−104.69
−65.56
4
Δη/mPa.s
298.15
3.0399 −2.0619
3.2095 −2.9280
3.5455 −3.0034
−0.4829
−0.4418
0.4745 −0.3927
−0.8967 0.04
0.5433 0.03
2
+DMSO 303.15
308.15
TEAA
+DMSO 303.15
308.15
0.7425 0.05
0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
298.15
0.4310
0.3787
−0.5648 0.003
−0.2921 0.004
0.1573 0.007
x
1
b
25
20
15
10
5
a
0.00
-0.05
-0.10
-0.15
-0.20
-0.25
0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
x
1
Fig. 3. Viscosities for the mixtures of ILs with DMSO vs. mole fraction of IL x1 for
(a) DEAA {(x1) 298.15 K (○) +, or (x1) 303.15 K (△) +, or (x1) 308.15 K (□)+DMSO
(x2)}, (b) TEAA {(x1) 298.15 K (○) +, or (x1) 303.15 K (△) +, or (x1) 308.15 K (□)+
DMSO (x2)}, at various compositions and atmospheric pressures. The solid line repre-
sents the smoothness of these data.
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
x
1
b
The following Redlich–Kister expression was used to correlate these
properties:
0.5
!
n
i
Y ¼ x1x2
a ðx −x Þ
ð6Þ
∑
0.4
0.3
0.2
0.1
0.0
i
1
2
i¼0
where Y refers to VE, ΔKs or Δη. ai are adjustable parameters and can
be obtained by least-squares analysis. Values of the fitted parameters
are listed in Table 2 along with the standard deviations of the fit. The
values of VE, ΔKs and Δη for the binary mixtures at various tempera-
tures as function of ILs concentrations are included in Table 1.
Figs. 4, 5 and 6 display the experimental data for the binary mixtures,
and the fitted curves, along with the excess properties of VE, ΔKs and
Δη for the ILs with DMSO as function of IL concentrations at different
temperatures, respectively.
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
As seen from the experimental results in Fig. 4, the values of VE for
DEAA or TEAA with DMSO are negative or positive, respectively in the
entire range of composition. It is more interesting to note that the VE
values in DEAA+DMSO or TEAA+DMSO systems have minimum or
maximum values at mole fractions of this ILs of about x1 ≈0.2000 or
x1 ≈0.5000 at investigated temperatures, respectively. The minimum
x
1
Fig. 4. Excess molar volumes (VE) for the mixtures of ILs with DMSO vs. mole fraction of
IL x1 for (a) DEAA{(x1) 298.15 K (○) +, or (x1) 303.15 K (△) +, DMSO (x2)}, (b) TEAA
{(x1) 298.15 K (○) +, or (x1) 303.15 K (△) +, DMSO (x2)}, at various compositions and
atmospheric pressures. Solid (—) lines correlated by Redlich–Kister equation.

V. Govinda et al. / Journal of Molecular Liquids 164 (2011) 218–225
223
a
a
0
-5
1.0
0.8
0.6
0.4
0.2
0.0
-10
-15
-20
-25
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
x
1
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
b
x
1
0.00
-0.02
-0.04
-0.06
-0.08
-0.10
-0.12
-0.14
-0.16
b
0
-10
-20
-30
-40
-50
-60
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
x
1
Fig. 6. Deviation in viscosities (Δη) for the mixtures of ILs with DMSO vs. mole fraction
of IL x1 for (a) DEAA {(x1) 298.15 K (○) +, or (x1) 303.15 K (△) +, or (x1) 308.15 K (□)+
DMSO (x2)}, (b) TEAA {(x1) 298.15 K (○) +, or (x1) 303.15 K (△) +, or (x1) 308.15 K (□) +,
DMSO (x2)}, at various compositions and atmospheric pressures. Solid (—) lines correlated
by Redlich–Kister equation.
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
x
1
Fig. 5. Deviation in isentropic compressibilities (ΔKs) for the mixtures of ILs with DMSO
vs. mole fraction of IL x1 for (a) DEAA {(x1) 298.15 K (○) +, or (x1) 303.15 K (△) +, or
(x1) 308.15 K (□) +, DMSO (x2)}, (b) TEAA {(x1) 298.15 K (○) +, or (x1) 303.15 K (△) +,
or (x1) 308.15 K (□)+DMSO (x2)}, at various compositions and atmospheric pressures.
Solid (—) lines correlated by Redlich–Kister equation.
interactions taking place in the mixture, which are the result of differ-
ent effects containing the loss of the DMSO dipole interaction from
each other (positive VE) and the breakdown of the ionic liquid ion–
pair (positive VE). The interaction between the ion–pair of ILs
increases as compared to IL+DMSO interactions, which leads to
positive contribution. This phenomenon is explicitly explained in
Scheme 1.
Fig. 5 illustrates the deviation in isentropic compressibility (ΔKs)
values over the whole composition range at various temperatures,
for all investigated systems as a function of ILs concentration. It is
clear that different phenomena of ΔKs were observed for the various
ILs with DMSO. The graphical representations in Fig. 5, the ΔKs values
are negative over the entire composition range at all the temperature
range and approach the minimum at x1 ≈0.3500 and x1 ≈0.2700 for
the system DEAA and TEAA with DMSO respectively. Clearly, we ob-
served only negative ΔKs values for the DEAA+DMSO and TEAA+
DMSO at all studied temperature range, respectively. The negative
values of the ΔKs of the DEAA or TEAA with DMSO imply that solvent
molecules around the solute are less compressible than the solvent
molecules in the bulk solutions.
increases and as temperature increases for DEAA+DMSO system at
all temperatures. This behavior can be explained in terms of hydrogen
bonding that is certainly more T-dependent than coulombic interac-
tions. The minimum can be due to hydrogen bonds between DMSO
molecules and DEAA, which is schematically shown in Scheme 1.
The negative excess molar volumes reveal that a more efficient pack-
ing or attractive interaction occurred when DEAA and DMSO were
mixed. The interactions between the DMSO molecules and the ions
of these ILs are due to ion–dipole interactions. This will reduce the hy-
drogen bond between the cation and anion in the ionic liquid, which
contribute to the negative VE values. On the other hand, the TEAA+
DMSO mixture reveals the positive values of VE. The observed positive
values show that there exist no specific interactions between unlike
molecules and also the compact structure of the polar component
(DMSO) due to dipolar association has been broken by these ILs.
The magnitude and sign of VE values are a reflection of the type of

224
V. Govinda et al. / Journal of Molecular Liquids 164 (2011) 218–225
Scheme 1. Schematic depiction of hydrogen bonding interactions between DEAA+DMSO and TEAA+DMSO, where colorrepresentations are as follows, green = carbon, white =
hydrogen, red = oxygen and yellow = sulfur.
The DEAA+DMSO system shows the positive viscosity deviation
at all investigated temperatures whereas the TEAA+DMSO mixture
reveals the negative viscosity deviation at all studied temperatures,
as shown in Fig. 6. In fact, temperature influences strongly on the vis-
cosity deviation. As the temperature increases, the deviations also in-
crease towards the positive values for TEAA+DMSO system.
Apparently, the viscosity of the pure ILs and their mixtures decreases
quickly when the temperature increases. This behavior agrees with
several reported literature that with increase in temperature the neg-
ative values Δη are progressively reduced and even reach positive de-
4. Conclusions
The work performed intends to map the thermophysical behavior
of two important ILs with DMSO at various temperatures. The values
of ρ, u and η for ILs with DMSO have been reported at 298.15 to
308.15 K under atmospheric pressure. From these measurements,
we have predicated VE, ΔKs and Δη at each temperature as a function
of IL concentration. The values of VE values for DEAA or TEAA with
DMSO are negative and positive at all the ranges of composition, re-
spectively, indicating negative deviations and positive deviations
from ideal behavior. We observed negative ΔKs values over the
whole composition range for the DEAA+DMSO and TEAA+DMSO
at all studied temperature range. The DEAA+DMSO system shows
the positive viscosity deviation while TEAA+DMSO system reveals
the negative viscosity deviation at all investigated temperatures. In
general, the Redlich Kister polynomial was used to correlate the
results and provides a good description for VE, ΔKs and Δη with
composition for both systems.
viation [14,15,26–28]. The minima lie at
a mole fraction of
approximately 0.2600 for TEAA+DMSO and maximum mole fraction
of about 0.3500 for DEAA+DMSO at 298.15 K. The change in the
magnitude of the positive Δη values as a function of temperature
can be attributed to the decrease in hydrogen bonding. By increasing
the temperature the interactions become very weak due to weaken-
ing of the dipolar association by the IL as well as the dissociation of
the ionic liquid ion–pair.

V. Govinda et al. / Journal of Molecular Liquids 164 (2011) 218–225
225
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xi
Vm
Vi
Mi
VE
Ks
ΔKs
ai
ultrasonic sound velocity
mole fraction of component i
molar volume of the mixture
molar volume of component i
molar mass of component i
excess molar volume
isentropic compressibility
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ρ
density
η
viscosity
Δη
σ
deviation in viscosity
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Subscripts
cal
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calculated from Eq. (6)
experimental
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We gratefully acknowledge the University Grants Commission
(UGC), New Delhi, Department of Science and Technology (DST), New
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Industrial Research (CSIR), New Delhi, grant no. 01(2343)/09/EMRII
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