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- Authors : N. Bhanu Murthy, M. Rangacharyulu, J. Siva Rama Krishna
- Paper ID : IJERTV6IS040534
- Volume & Issue : Volume 06, Issue 04 (April 2017)
- DOI : http://dx.doi.org/10.17577/IJERTV6IS040534
- Published (First Online): 21-04-2017
- ISSN (Online) : 2278-0181
- Publisher Name : IJERT
- License:
This work is licensed under a Creative Commons Attribution 4.0 International License
Excess Thermodynamic and Volumetric Properties of Binary Mixtures containing Ionic Liquid [Bmim][NTf2]and Dimethyl Carbonate from T = (298.15to 323.15) K
N. Bhanu Murthy1, M. Rangacharyulu2, J. Siva Rama Krishna2* 1Department of Physics, Acharya Nagarjuna University, 2Department of Physics, Acharya Nagarjuna University
Abstract – The density (), ultrasonic velocity (u) and refractive index (nD) of the binary mixtures of 1-Butyl 3- Methylimidazolium bis (Trifluoromethylsulfonyl)Imide (Bmim [NTf2]) and dimethyl carbonate (DMC)and those of pure liquids were measured using Anton Paar vibrating tube density and sound velocity meter (DSA 5000 M) and Dr. Kernchen Abbemat (Anton Paar, Austria) refractometer over the whole composition range as a function of temperature between 298.15 and 323.15 K in steps of 5K at atmospheric pressure. From the experimental data, the excess values of
molar volumes ( ), partial molar volume( ), partial molar
polarity is between that of the water and chlorinated organic solvents.
Solvent feature of ionic liquid comes from H- bond donation from cation, H-bond accepting functionality of the anion, and – bonding. ILs are immiscible to non polar organic solvents and can be used in two phase system.
They have applicable electrochemical window. For some ILs it is in the range of ~6V [3]. However
volume at infinite dilution(,), isentropic compressibility ( ), acousticimpedance (ZE), free length ( ), speeds of sound (uE), and deviations in refractive index ( ) were calculated and fitted to a RedlichKister type equation. The
negative values of , , and positive values of ZE, uE,
choice of electrode has some effect on the electrochemical window. Ionic liquids like ammonium, piperidinium, morpholinium with 4 coordinated nitrogen have larger electrochemical window compared to others [3].
In the present work BMIM imide ionic liquid
and indicate the existence of strong interactions between the components.
Keywords: Bmim imide, dimethyl carbonate, Density, ultrasonic velocity, Refractiveindex, excess/deviation parameters, Redlich Kister type equation.
INTRODUCTION
Since Ionic liquids (ILs) have large variety of new applications, a major focus of study is being carried out both at laboratory and industrial scale. The interesting properties such as negligible volatility or non-flammability make them suitable for the replacement of conventional liquids.
The measurement of physical properties is one of the most important research areas involving ILs for the use of them from laboratory level to industrial applications.
Basing on how they attain the charge, Ionic liquids are divided into three types:
(1) protic; (2) aprotic; and (3) zwitter ionic.
Protic ILs are formed by proton-transfer reaction as acid and base as they donate and accept hydrogen bonds making hydrogen bonded network like water [1]. Aprotic ILs consist of imidazolium and pyrrolidium based cations and form inter molecular hydrogen bonds but not as protic ILs.
Polarity is an important parameter to describe nature of a solvent. Ionic liquids are considered to be highly polar but weak as coordinating solvent [2]. Their
was mixed with well known green solvent dimethyl carbonate in different proportions and the density, sound velocity and refractive index were measured for each mixture at six temperatures in steps of 5K from 298.15K to 323.15K.
[Bmim] [NTf2] has many applications such as extracting solvent for the removal of many organic compounds through liquidliquid extraction [4, 5], in chromatography [6] and enzyme catalysis in ionic liquids [7], etc.Dimethyl carbonate (DMC) can be used as an anti-knocking agent and can possibly (partially) replace MTBE or ethanol as a fuel additive [8]. In addition, DMC can potentially replace dimethyl sulfate and methyl halides in methylation reactions [9]. It may also be suitable to replace phosgene as a carbonylation agent for the production of polycarbonates and urethane polymers [9]. DMC is relatively non toxic, especially in comparison to the mentioned chemicals [10]. It is of great importance to understand the mixing behavior of ILs in dimethyl carbonate and to provide accurate physicochemical data. The thermo acoustic, volumetric and refractive index data of [Bmim][NTf2] with dimethyl carbonate were not reported earlier.
Basing on our preliminary experiments, [Bmim][NTf2] was foun- d to be miscible with dimethyl Carbonate at all proportions. Hence, it is proposed to measure the densities (), speeds of sound(u), refractive
indices (nD) of the binary mixtures of [Bmim][NTf2] with dimethyl carbonate in the temperature range from 298.15 to
Chemicals:
2 EXPERIMENTAL
-
K and over the whole composition range and to estimate their excess/deviation properties for their potential application in industrial processes. On the basis of the measured values the properties such as excess values of molar volumes( ), partial molar volumes , partial molar volumes at infinite dilution (,) , isentropic
compressibility(), acoustic impedance (ZE), free length ( ), speeds of sound (uE), and deviations in refractive
index nD for binary mixtures were fitted using Redlich Kister type polynomial equation.
The ionic liquid, (BMIM imide) or [Bmim][NTf2] , with purity 0.99 in mass fraction was used in this work. It was purchased from Iolitec, GmBH (Germany), while the dimethyl carbonate was supplied by Sigma Aldrich. The IL [Bmim][NTf2] was used without any further purification and dimethyl carbonate was further purified by distillation. The measured density, speed of sound and refractive index of the pure liquids at atmospheric pressure are compared with literature values to verify the purity of liquids under investigation and are presented in table 1. Ever since the concept of hindered internal rotation about single bonds was established, it has been expected that esters of simple carboxylic acids might exist in a conformational equilibrium in their fluid states. Such equilibrium is expected, on theoretical grounds, to involve the two planar conformations for DMC (shown in fig.1d).
Fig1a: Ball and stick model of Bmim NTf2 Fig 1b: 1-Butyl 3-Methylimidazolium cation
Fig1c: molecular structure of dimethyl carbonate Fig 1d: molecular conformations of dimethyl carbonate
Table 1: Experimental and literature values of density, velocity and refractive index at temperatures 298.15K to 323.15K
kgm-3 u ms-1 nD
T/K
Exp.
Lit.
Exp.
Lit.
Exp.
Lit.
[Bmim][NTf2] 298.15
1433.72
1433.72[11]
1227.86
1227.86[11]
1.4268
1.4267[11]
303.15
1428.92
1428.95[11] 1216.77
1216.77[11] 1.4250 1.4252[11]
308.15
1424.13
1424.18[11] 1205.8
1205.80[11] 1.4230 1.4237[11]
313.15 1419.36 1419.41[11] 1194.95 1194.95[11] 1.4220 1.4223[11]
318.15 1414.61 1414.64[11] 1184.23 1184.23[11] 1.4190 1.4208[11]
323.15 1409.88 1409.87[11] 1173.61 1173.61[11] 1.4180 1.4192[11]
Dimethyl carbonate
td> 1063.43 1063.
39[12] 1198.87 119
8[16] 1.3664
1056.82 1056.
35[13] 1177.29 117
7[16] 1.3641
1050.18 1050.
14 [12] 1155.63 115
5[16] 1.3618
1043.50 1043.
10[14] 1134.23 113
4[16] 1.3594
1036.79 1035.
60[15] 1113.09
– 1.3570
1.3664[13]
1.3652[17]
1.3644[17]
1.3624[17]
1.3622[17]
1.3590[17]
298.15
303.15
308.15
313.15
318.15
323.15 1030.04 1028.40[15] 1092.16 – 1.3547
-
THEORY:
The experimentally measured values of , u and nD were used to calculate the values of thermodynamic and
V E 2 x M 1 1
m i i
i1 i
(3)
acoustical parameters such as molar volume (Vm), intermolecular free length (Lf), isentropic compressibility (kS). The derived excess/deviation parameter values are shown in Table 2.
The excess/deviation parameters for the above parameters including deviations in refractive index
VE
Where is the density of the mixture and Mi, xi and i are the molar mass, mole fraction, and density of the ith component in the mixture, respectively.
The isentropic compressibility, kS, is computed directly from the measured values of speed of sound and density
nD, ( m)
T
were also calculated by using the following
using the NewtonLaplace equation:
equations:
= 1
1 = ( ) (4)
= (1)
Where Meff is the effective molecular weight (= x1M1 +
( )
= (2)
2
x2M2), where M1 and M2 are the molar masses and x1 and x2 are the mole fractions of IL and dimethyl carbonate,
Excess isentropic compressibility is given
respectively), and is the density of the medium.
The speed of sound (u) and the density of the medium ()
by: k E
S
kS xi kSi
2
i1
(5)
using NewtonLaplace equation give the intermolecular free length as:
Where, kS is the isentropic compressibility
The excess intermolecular free length is given by:
= u2 (2)
Where, K is a temperature dependent constant equal to
=
[11
+ 22
] (6)
(93.875 + 0.375T) x 10-8.
The excess molar volumes are given by:
The excess speeds of sound, uE are estimated in binary mixtures using the following expression proposed by Douheret et al. [18]:
= [11 + 22]
(7)
Table 2: The excess parameters of binary mixtures of BMIM imide and dimethyl carbonate.
x U k *10-10 ZE*10-5 *10-10m n R *10-3 *10-3
1 s
m
m/s m2 N-1 Kg/m2 .s m3/mol m3mol-1
0.0000
0.0000
0.0000
29
0.0000
8.15K
0.0000
0.0000
0.0000
0.0000
0.1010
12.8047
-0.5778
0.1030
-0.0236
0.0142
0.0461
0.0461
0.1945
20.4161
-0.8050
0.1519
-0.0334
0.0198
0.0512
0.0512
0.2994
22.7964
-0.8617
0.1712
-0.0362
0.0215
0.0429
0.0429
0.3999
20.7558
-0.8132
0.1678
-0.0344
0.0208
0.0339
0.0339
0.4976
17.1026
-0.7195
0.1525
-0.0306
0.0190
0.0272
0.0272
0.5842
13.8382
-0.6168
0.1331
-0.0262
0.0166
0.0222
0.0222
0.6886
10.3700
-0.4775
0.1051
-0.0204
0.0131
0.0153
0.0153
0.8014
6.5662
-0.3122
0.0700
-0.0134
0.0087
0.0064
0.0064
0.8890
3.1392
-0.1757
0.0399
-0.0075
0.0051
0.0005
0.0005
1.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
303.15K
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.1010
15.0762
-0.6359
0.1043
-0.0257
0.0147
0.0593
0.0593
0.1945
23.7000
-0.8837
0.1539
-0.0363
0.0205
0.0793
0.0793
0.2994
26.5399
-0.9451
0.1737
-0.0394
0.0222
0.0730
0.0730
0.3999
24.5321
-0.8926
0.1705
-0.0375
0.0214
0.0540
0.0540
0.4976
20.6386
-0.7907
0.1552
-0.0333
0.0193
0.0352
0.0352
0.5842
16.9889
-0.6784
0.1356
-0.0286
0.0169
0.0233
0.0233
0.6886
12.9079
-0.5256
0.1071
-0.0223
0.0133
0.0146
0.0146
0.8014
8.3429
-0.3443
0.0715
-0.0146
0.0089
0.0071
0.0071
0.8890
4.2584
-0.1950
0.0409
-0.0083
0.0052
0.0003
0.0003
1.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
308.15K
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.1010
17.2744
-0.6989
0.1054
-0.0278
0.0152
0.0752
0.0752
0.1945
27.0122
-0.9700
0.1559
-0.0394
0.0212
0.1033
0.1033
0.2994
30.3474
-1.0366
0.1763
-0.0427
0.0229
0.0993
0.0993/p>
0.3999
28.3119
-0.9790
0.1732
-0.0406
0.0220
0.0764
0.0764
0.4976
24.0985
-0.8674
0.1577
-0.0361
0.0198
0.0505
0.0505
0.5842
20.0194
-0.7443
0.1378
-0.0311
0.0172
0.0315
0.0315
0.6886
15.3092
-0.5766
0.1089
-0.0242
0.0135
0.0167
0.0167
0.8014
9.9657
-0.3779
0.0728
-0.0159
0.0090
0.0081
0.0081
0.8890
5.2075
-0.2143
0.0416
-0.0090
0.0053
0.0033
0.0033
1.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
313.15K
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.1010
19.3383
-0.7660
0.1064
-0.0301
0.0159
0.1011
0.1011
0.1945
30.1866
-1.0623
0.1577
-0.0427
0.0220
0.1343
0.1343
0.2994
34.0354
-1.1349
0.1787
-0.0463
0.0236
0.1295
0.1295
0.3999
31.9856
-1.0717
0.1757
-0.0441
0.0226
0.1026
0.1026
0.4976
27.4678
-0.9497
0.1601
-0.0392
0.0203
0.0689
0.0689
0.5842
22.9806
-0.8150
0.1400
-0.0337
0.0176
0.0407
0.0407
0.6886
17.6696
-0.6314
0.1107
-0.0263
0.0137
0.0155
0.0155
0.8014
11.5609
-0.4138
0.0740
-0.0173
0.0091
0.0032
0.0032
0.8890
6.1230
-0.2348
0.0423
-0.0098
0.0053
0.0023
0.0023
1.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
318.15K
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.1010
21.0881
-0.8355
0.1069
-0.0324
0.0166
0.1249
0.1249
0.1945
33.1742
-1.1605
0.1593
-0.0460
0.0228
0.1669
0.1669
0.2994
37.6602
-1.2406
0.1810
-0.0500
0.0244
0.1633
0.1633
0.3999
35.6027
-1.1714
0.1781
-0.0477
0.0233
0.1324
0.1324
0.4976
30.7489
-1.0376
0.1623
-0.0424
0.0208
0.0917
0.0917
0.5842
25.8536
-0.8904
0.1420
-0.0365
0.0180
0.0556
0.0556
0.6886
19.9882
-0.6902
0.1124
-0.0284
0.0140
0.0200
0.0200
0.8014
13.1508
-0.4527
0.0753
-0.0187
0.0092
-0.0021
-0.0021
0.8890
7.0069
-0.2567
0.0430
-0.0106
0.0054
-0.0060
-0.0060
1.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
323.15K
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.1010
23.0531
-0.9141
0.1078
-0.0351
0.0174
0.1585
0.1585
0.1945
36.1970
-1.2678
0.1609
-0.0498
0.0237
0.2105
0.2105
0.2994
41.1885
-1.3542
0.1830
-0.0542
0.0253
0.2070
0.2070
0.3999
39.1366
-1.2784
0.1804
-0.0516
0.0240
0.1715
0.1715
0.4976
34.0006
-1.1325
0.1645
-0.0460
0.0215
0.1246
0.1246
0.5842
28.7112
-0.9719
0.1440
-0.0396
0.0185
0.0821
0.0821
0.6886
22.2596
-0.7532
0.1140
-0.0308
0.0143
0.0384
0.0384
0.8014
14.6873
-0.4940
0.0764
-0.0203
0.0094
0.0083
0.0083
0.8890
7.9013
-0.2804
0.0436
-0.0115
0.0055
-0.0008
-0.0008
1.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
Table 3: coefficients (Ai) of RedlichKister polynomial for excess parameters
VmE(*10-3 m3mol-1)
RKC/Tem
A0
A1
A2
A3
A4
298.15
-0.0036
-0.0026
-0.0028
-0.0009
0.0001
0.0000077
303.15
-0.0038
-0.002
-0.0026
-0.0009
-0.0006
0.0000098
308.15
-0.004
-0.0029
-0.003
-0.001
-0.0002
0.0000095
313.15
-0.0042
-0.003
-0.003
-0.0012
-0.0005
0.0000067
318.15
-0.0044
-0.0032
-0.0032
-0.0012
-0.0004
0.0000095
323.15
-0.0047
-0.0034
-0.0032
-0.0012
-0.0006
0.0000100
U ( m/s)
298.15
68.03
78.36
74.73
-14.04
-73.94
0.371650
303.15
82.14
85.68
78.21
-12.15
-69.26
0.310580
308.15
95.94
94.37
83.35
-11.4
-69.71
0.320470
313.15
109.38
102.66
88.66
-11.08
-71.84
0.334690
318.15
122.46
111.37
95.81
-14.45
-80.72
0.394440
323.15
135.43
119.26
100.22
-14.41
-81.85
0.409580
ks(*10-10 m2 N-1)
298.15
-2.8673
-2.2132
-1.7337
-1.0524
-0.2247
0.001590
303.15
-3.1512
-2.4128
-1.8744
-1.1771
-0.3334
0.001210
308.15
-3.457
-2.6435
-2.0486
-1.3062
-0.4018
0.001320
313.15
-3.7848
-2.8912
-2.2401
-1.4415
-0.4586
0.001510
318.15
-4.1353
-3.1648
-2.4716
-1.5496
-0.4447
0.002090
323.15
-4.5136
-3.4515
-2.6897
-1.7165
-0.5302
0.002250
ZE*10-5 Kg/m2.s
298.15
0.60805
0.39801
0.26675
0.09804
-0.02633
0.00034
303.15
0.61872
0.40144
0.26571
0.09555
-0.02112
0.00027
308.15
0.62867
0.40664
0.26852
0.09212
-0.02618
0.00027
313.15
0.63825
0.41091
0.27134
0.08990
-0.03208
0.00029
318.15
0.64721
0.41599
0.27637
0.08149
-0.04611
0.00036
323.15
0.65590
0.41967
0.27684
0.07797
-0.04860
0.00039
LfE*10-10m
298.15
-0.1218
-0.0923
-0.0708
-0.0362
-0.0017
0.000088
303.15
-0.1327
-0.0997
-0.0758
-0.0400
-0.0043
0.000076
308.15
-0.1440
-0.1079
-0.0833
-0.0432
-0.0022
0.000085
313.15
-0.1562
-0.1167
-0.0910
-0.0463
-0.0013
0.000097
318.15
-0.1690
-0.1263
-0.0969
-0.0485
-0.0018
0.000111
323.15
-0.1832
-0.1366
-0.1036
-0.0525
-0.0043
0.000126
298.15
0.0756
0.0476
0.0328
0.0292
0.0183
0.000050
303.15
0.0772
0.0509
0.0377
0.0285
0.0144
0.000056
308.15
0.0790
0.0537
0.0393
0.0286
0.0158
0.000070
313.15
0.0809
0.0567
0.0401
0.0305
0.0200
0.000070
318.15
0.0831
0.0596
0.0412
0.0328
0.0222
0.000099
323.15
0.0856
0.0624
0.0432
0.0360
0.0256
0.000129
Rm*10-3 m3/mol
298.15
0.1084
0.119
0.1572
0.3123
0.1111
0.00495
303.15
0.1393
0.3318
0.4637
0.1261
-0.2718
0.00485
308.15
0.1995
0.4968
0.495
0.0044
-0.2107
0.00479
313.15
0.2724
0.6919
0.4106
-0.0173
0.0903
0.00385
318.15
0.3627
0.8606
0.3977
0.0652
0.0984
0.00608
323.15
0.4934
1.0005
0.4812
0.1594
0.1649
0.00827
n
If the difference between the refractive indices of the two components is small then thedeviation in refractive index of binary mixtures containing ILs is given by:
= [11 + 21] (8)
-
RESULTS AND DISCUSSION
-
In the present study, excess molar volume ( ), excess partial molar excess volume ( ) , partial molar excess volume at infinite dilution (,), excess isentropic
compressibility ( ), excess free length ( ), excess
The excess/deviation properties have been fitted to a RedlichKister type polynomial equation given by:
= 12 (2 1) (9)
=0
Where, x1 and x2 are the mole fraction of ionic liquid and dimethyl carbonate, respectively and the Ai are adjustable parameters of the function and are determined using the leastsquares method. In the present investigation the i values ave been taken from 0 to 4. The corresponding standard deviations (YE) have been calculated using the followingexpression:
(YE YE )
acoustic impedance (ZE), excess ultrasonic velocity (uE), and deviations in refractive index () were calculated. The strength of interactions present between the component molecules of the binary mixture under study is indicated by the variations observed in these excess/deviation parameters. Further these variations are effected by the composition, molecular size, shape and temperature. The physical, chemical, and structural contributions [18, 19] influence these thermodynamic parameters.
Excess molar volumes for binary mixture of [Bmim][NTf2] and dimethyl carbonate as a function of composition from 298.15 to 328.15 K are shown in Fig. 1. The contraction in the volume of the mixture can be attributed to the formation of hydrogen bonds between the ionic liquid [Bmim][NTf2] and dimethyl carbonate.
(YE) = { exp cal } (10)
The values of become more negative with
mn
where m is the total number of experimental points and n is the number of coefficients in eq.(22). The calculated values of the coefficients Ai along with the standard deviations, (YE)are given in Table 4.
increase in temperature. This is due to the fitting of smaller dimethyl carbonate molecules into the voids created by larger IL molecules leading to decrease in volume of the mixture to a greater extent, which results in more negative
values with increase in temperature.
0.0001
mole fraction of BMIM imide
-0.0001 0.0
0.2
0.4
0.6
0.8
1.0
-0.0003
-0.0005
-0.0007
-0.0009
-0.0011
-0.0013
-0.0015
298.15K
303.15K
308.15K
313.15K
318.15K
323.15K
Excess molar volume (10-3m3 mol-1)
Fig. 2: Plots of excess molar volume () against mole fraction (x1) for binary mixtures of [Bmim][NTf2] and Dimethyl carbonate at temperature T and atmospheric pressure.
The strength of interaction follows the order:
Where and are the molar volumes of pure
1 2
(323.15>318.15>313.15>308.15>303.15>298.15) K. The
properties of partial molar volumes reflect the existing molecular interactions in the system. The contribution of a
components of [Bmim][NTf2] and dimethyl carbonate respectively. Differentiating the RedlichKister equation
for , we get the derivatives ( ) mentioned in the
component of a mixture to the overall volume of the
x1
,
solution is interpreted in terms of Partial molar volume. Therefore, the partial molar volume is a function of composition of the mixture. The partial molar volumes
equations (11) and (12) are obtained by, which leads to the following equations for ,1, ,2:
4
of component 1[Bmim][NTf ] and of component
,1 = + 2 (2 1) 4
,1
2 ,2
1 2
2 2 ()(
)1
2 (dimethyl carbonate) in the mixtures over the entire range of composition have been calculated by using the following equations:
=0
1 2
=1
2 1
(13)
Table 5: Partial molar volumes (,1, ,2 against
,1 = + + (
)
(11)
mole fraction x ) for [Bmim][NTf ] and dimethyl
1
2 x1
, 1 2
carbonate mixtures at temperature T and atmospheric pressure:
,2 = + ( )
(12)
2 1 x1
,
298.15K 303.15K 308.15K 313.15K 318.15K 323.15K
x Vm,1 Vm,2 Vm,1 Vm,2 Vm,1 Vm,2 Vm,1 Vm,2 Vm,1 Vm,2 Vm,1 Vm,2
10-6m3mol-1 10-6m3mol-1 10-6m3mol-1 10-6m3mol-1 10-6m3mol-1 10-6m3mol-1
0.0000 |
289.6753 |
84.7069 |
290.2161 |
85.2368 |
291.2702 |
85.7760 |
291.9740 |
86.3250 |
292.8900 |
86.8837 |
293.5233 |
87.4529 |
0.1010 |
290.2420 |
84.6762 |
291.1750 |
85.2028 |
291.9834 |
85.7437 |
292.8723 |
86.2926 |
293.7347 |
86.8498 |
294.6158 |
87.4143 |
0.1945 |
290.6148 |
84.6124 |
291.5405 |
85.1476 |
292.3743 |
85.6794 |
293.2657 |
86.2320 |
294.1386 |
86.7855 |
295.0418 |
87.3498 |
0.2994 |
290.8308 |
84.5448 |
291.6912 |
85.0939 |
292.5899 |
85.6092 |
293.4643 |
86.1628 |
294.3464 |
86.7156 |
295.2249 |
87.2847 |
0.3999 |
290.9022 |
84.5086 |
291.7564 |
85.0518 |
292.6748 |
85.5623 |
293.5584 |
86.1056 |
294.4357 |
86.6634 |
295.3081 |
87.2316 |
0.4976 |
290.9488 |
84.4698 |
291.8400 |
84.9801 |
292.7461 |
85.5024 |
293.6519 |
86.0263 |
294.5253 |
86.5876 |
295.4128 |
87.1422 |
0.5842 |
291.0535 |
84.3426 |
291.9794 |
84.8107 |
292.8752 |
85.3458 |
293.7956 |
85.8518 |
294.6780 |
86.4023 |
295.5851 |
86.9330 |
0.6886 |
291.3290 |
83.8449 |
292.2725 |
84.2660 |
293.1807 |
84.7881 |
294.1064 |
85.2746 |
295.0197 |
85.7743 |
295.9474 |
86.2606 |
0.8014 |
291.8079 |
82.3974 |
292.7519 |
82.7678 |
293.7003 |
83.1984 |
294.6341 |
83.6283 |
295.5920 |
84.0091 |
296.5409 |
84.4086 |
0.8890 |
292.2160 |
80.1124 |
293.1728 |
80.3718 |
294.1495 |
80.6678 |
295.1071 |
80.9382 |
296.0906 |
81.1889 |
297.0620 |
81.4444 |
1.0000 |
292.4976 |
74.8593 |
293.4814 |
74.6123 |
294.4675 |
74.7296 |
295.4569 |
74.3886 |
296.4490 |
74.4948 |
297.4435 |
74.3206 |
4
2 1
,2 = + 2 (2 1)
=0
4
1
+ 222 ()(2
which represents the contraction of volume on mixing [Bmim][NTf2] with dimethyl carbonate at all the temperatures under study.
The variation of excess partial molar volumes of
=1
[Bmim][NTf2] and (dimethyl carbonate) are
)1 (14)
,1
,2
1
Using the above equations, have been
represented in Figures 3 and 4 respectively, in the
temperature range from 298.15 to 323.15K. Inspection of
evaluated using:
,1
,2
these figures not only reveals the existence of strong forces between the unlike molecules but also supports the
,1 1
= ,1 (15)
= ,2 (16)
deductions drawn from excess molar volume. The partial molar volumes and excess partial molar volumes of
[Bmim][NTf ] at infinite dilution,( ) and ( ), are,2
The values of
2
and
are presented in Table 5 for all
2
given by:
,
,1
,2
,1
,2
= 0 + 1 + 2 + 3 + =
the systems. From this table, we observe that the values of
,1
,1 1
,1
and ,2
for both the components in the mixtures are
(17)
lower than their individual molar volumes in the pure state,
The data of and (,) are presented in Table 6 at
conclude that with increasing temperature, strong
,1 ,1
1.0
0.8
0.6
0.4
0.2
0.0
-0.0005
0.0000
,1
298.15K to 323.15K in steps of 5 K. From this table, the values of (,) are found to be negative and become more negative with increasing temperature. Hence we can
interactions increase among the unlike molecules of the mixtures. This supports the existing strong molecular interactions that were observed with the variation of .
0.0005
Molefraction of BMIM imide
298.15K
303.15K
308.15K
313.15K
318.15K
323.15K
-0.0020
-0.0040
-0.0060
-0.0080
-0.0100
1.0
0.8
0.6
0.4
0.2
0.0
0.0000
-0.0035
-0.0040
298.15K
303.15K
308.15K
313.15K
318.15K
323.15K
-0.0010
-0.0015
-0.0020
-0.0025
-0.0030
excess partial molar volume-2 (10-3m3
excess partial molar volume-1 (10- 3m3 mol-1)
mol )
-1
,1
Fig. 3: Plots of excess partial molar volume ( ) against mole fraction x1 for [Bmim][NTf2] and Dimethyl carbonate mixtures at temperature T and atmospheric pressure
Molefraction of BMIM imide
-0.0120
-0.0140
,2
Fig. 4: Plots of excess partial molar volume ( ) against mole fraction (x1) for [Bmim][NTf2] and dimethyl carbonate mixtures at temperature T and atmospheric pressure
Table 6: Partial ( ) and excess partial molar volumes (( )) at infinite dilution for [Bmim][NTf2] (1) Dimethyl
,1 ,1
carbonate(2) mixtures at temperature T and atmospheric pressure
T/K |
, |
, |
||
10-6m3mol-1 |
10-6m3mol-1 |
10-6m3mol-1 |
10-6m3mol-1 |
|
298.15 |
289.68 |
-2.82 |
74.86 |
-9.85 |
303.15 |
290.22 |
-3.27 |
74.61 |
-10.62 |
308.15 |
291.27 |
-3.2 |
74.73 |
-11.05 |
313.15 |
291.97 |
-3.48 |
74.39 |
-11.94 |
318.15 |
292.89 |
-3.56 |
74.49 |
-12.39 |
323.15 |
293.52 |
-3.92 |
74.32 |
-13.13 |
,1
,1
,2
,2
1.0
0.8
0.6
0.4
0.2
0.0
0.00
Mole fraction of BMIM imide
Deviation in isentropic compressibility
(10-10m2 N-1)
In Fig. 4, the values for this system are found to be negative in the whole composition range at all investigated temperatures. The negative values are attributed to the strong attractive interactions between the molecules of the
components [20]. In the present study, the negative values can be attributed to a closer approach of unlike molecules and a stronger interaction between components of mixtures at all temperatures. This supports the inference drawn from .
-0.20
-0.40
-0.60
-0.80 298.15K
303.15K
-1.00 308.15K
313.15K
-1.20 318.15K
-1.40 323.15K
Fig. 4: Plots of excess isentropic compressibility () against mole fraction (x1) for [Bmim][NTf2] and dimethyl carbonates mixtures at temperature T and atmospheric pressure
In the present study, the negative were observed. The trend of values (Fig. 5) is similar to that
among the components of a mixture cause the formation of molecular aggregates and more compact structures due to
of
at all temperatures under study. The specific
which the ultrasonic velocity increases leading to positive
uE. On the other hand, if the structure-breaking factor
interactions between unlike molecules in the liquid mixture lead to negative values of . The structural readjustments in the liquid mixture towards a less compressible phase of
fluid and closer packing of molecules [20] also contribute to negative .
Figure 6 shows that ZE is positive for the systems at all the temperatures under study. Specific acoustic impedance is a parameter that depends on the molecular packing of the mixture. The positive values of ZE indicate the presence of strong interactions between the component molecules [18].
From the figure 7 the uE values are found to be positive over the entire range of composition at all investigated temperatures. This indicates the increasing strength of interaction between component molecules of binary liquid mixtures. In general, strong interactions
predominates, it leads to expansion of the liquid mixture, and hence the ultrasonic velocity decreases resulting in negative uE [20]. The positive values of uE in the present system indicate much stronger interactions between the molecules [21].
Fig.8 shows that the values of are positive over the entire range of compositions at a given temperature. The variation of refractive index deviations with the mole fraction of IL shows the reverse trend to
[22]. This further supports the presence of strong interactions between component molecules in study.
Generally, the cohesive forces (attraction forces) or dispersive forces between the molecules of a mixture cannot be easily assessed by any theory.
Mole fraction of BMIM imide
0.000
0.0
0.2
0.4
0.6
0.8
1.0
-0.010
-0.020
-0.030
-0.040
-0.050
298.15K
303.15K
308.15K
313.15K
318.15K
323.15K
-0.060
298.15K
303.15K
308.15K
313.15K
318.15K
323.15K
0.20
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
excess Free length (0A)
excess Acoustic impedance (106Kg/m2
.s)
Fig. 5: Plots of excess free length (LEf) against mole fraction (x1) for [Bmim][NTf2] and Dimethyl carbonate mixtures at temperature T and atmospheric pressure
0.0 0.2 0.4 0.6 0.8 1.0
Mole fraction of BMIM imide
deviation in speed of sound (m/s)
Fig. 6: Plots of excess acoustic impedance (ZE) against mole fraction (x1) for [Bmim][NTf2 (1) dimethyl carbonate (2) mixtures at temperature T and atmospheric pressure
45.00
40.00
35.00
30.00
25.00
20.00
15.00
10.00
5.00
0.00
298.15K
303.15K
308.15K
313.15K
318.15K
323.15K
0.0 0.2 0.4 0.6 0.8 1.0
Mole fraction of BMIM imide
Fig. 7: Plots of excess ultrasonic speed of sounds (uE) against mole frction (x1) for [Bmim][NTf2]
0.030
0.025
0.020
298.15K
303.15K
308.15K
313.15K
318.15K
323.15K
0.0
0.2
0.4
0.6
0.8
1.0
Mole fraction of BMIM imide
0.015
0.010
0.005
0.000
deviation in refractive index
Fig. 8: Plots of deviation in refractive index () against mole fraction (x1) for [Bmim][NTf2] and Dimethyl carbonate mixtures at temperature T and atmospheric pressure
The electronic structure of the aromatic cations reflect the unique properties of imidazolium cations. The delocalized 3-center-4-electron configuration are contained in the electronic structure of these salts across the N1C2 N3 moiety, a double bond between C4 and C5 at the opposite side of the ring, and a weak delocalization in the central region [23]. Almost the same charge is carried by the hydrogen atoms C2H, C4H, and C5H, but carbon C2 is positively charged owing to the electron deficit in the
C=N bond. On the other hand C4 and C5 are practically
temperature, strong interactions increase among the unlike molecules of the mixtures. This supports the existing strong molecular interactions that were observed with the variation of .
-
In the present study, the negative values can be attributed to a closer approach of unlike molecules and a stronger interaction between components of mixtures over the entire range of composition at all temperatures under study.
-
The negative were observed. The trend of values
neutral. The properties of these ionic liquids arise from the resulting acidity of the hydrogen atoms. The hydrogen on the C2 carbon (C2H) has been shown to bind specifically with solute molecules.
The hydrogen bonds play an important role in the stability and miscibility of the binary liquid mixtures of [Bmim][NTf2] (1) and dimethyl carbonate(2). The nature of interaction of dimethyl carbonate molecules with the cation is different from that of anion. The characteristic groups which interact with dimethyl carbonate molecules are the CH groups in the imidazolium ring and oxygen atoms in the anion. The complete miscibility and solvation of cations and anions in the ionic liquid is due to sufficient hydrogen bonding interactions of dimethyl carbonate with [Bmim][NTf2]. Hence, the remarkable contraction in the volume of the mixture can be attributed to the hydrogen bonds between the ionic liquid [Bmim][NTf2] (1) dimethyl carbonate (2).
5 CONCLUSION
-
From the experimental data, parameters such as ,
(Fig. 5) is similar to that of at all temperatures under study.
-
ZE is positive for the systems at all the temperatures under study. The positive values of ZE indicate the presence of strong interactions between the component molecules.
-
Similarly the positive values of uE indicate much stronger interactions between the molecules.
-
The positive values of at a given temperature over the entire composition range indicate the strong interactions between the component molecules
-
Finally it may be concluded that the observed negative values of , , , and positive values of ZE, uE, clearly indicate the dominance of strong attractive forces.
ACKNOWLEDGEMENTS:
One of the authors (NBM) thanks Acharya Nagarjuna University authorities for providing the UGC-BSR meritorious fellowship.
, , ZE, uE,
, have been evaluated. The excess
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