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Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

The Thermodynamic and Excess Properties of Trialkyl-Substituted Imidazolium-Based Ionic Liquids with Thiocyanate and Its Binary Systems with Acetonitrile Qingguo Zhang,*,† Tongtong Xu,‡ Xinyuan Zhang,† Huige Yang,‡ and Wenbo Zhang‡ †

College of New Energy, Bohai University, Jinzhou 121013, Liaoning Province, China College of Chemistry and Chemical Engineering, Bohai University, Jinzhou 121013, Liaoning Province, China

‡

S Supporting Information *

ABSTRACT: Two kinds of new ionic liquids (ILs), 1,2-dimethyl-3-propylimidazolium thiocyanate ([C3mmim][SCN]) and 1-butyl-2,3-dimethylimidazolium thiocyanate ([C4mmim][SCN]), were synthesized and characterized by various methods. Then, the [C3mmim][SCN] and [C4mmim][SCN] were blended with acetonitrile (ACN) to prepare binary IL-based mixture systems over the whole concentration range (molar ratio of IL from 1 to 0). The densities, electrical conductivities, and dynamic viscosities of two pure ILs and two binary systems were determined from 288.15 to 323.15 K. The measured values of the surface tension are used in the calculation of interstice model. The temperature dependence of the transport properties (dynamic viscosity and electrical conductivity) is described by the Vogel−Fulcher−Tamman (VFT) equation and the Arrhenius equation, respectively. The volumetric properties like the thermal expansion coefficient, molecular volume, standard molar entropy, and lattice energy of the ILs are estimated through the empiric/semiempirical methods. The excess molar volumes (VE) and dynamic viscosity deviations (Δη) of the mixtures are calculated. For further research, the Redlich−Kister polynomial equation is used to fit the excess molar volume and the deviation in dynamic viscosity data. The negative values of the entire composition range of excess properties clearly indicate the existence of molecular interactions between the studied components.

1. INTRODUCTION Ionic liquids (ILs) are salts that are composed entirely of ions.1 Their unique properties such as extremely high thermal stability, low melting points, negligible vapor pressure, wide liquid range, good solvent behavior, wide electrochemical window, and high electrical conductivity make the possibility of using them as prospective “green solvents”.2−7 The relative low viscosity, low melting point, and desired conductivity push the 1,3-alkyl-substituted ILs into the upsurge group of imidazolium-based ILs, and the studies of their physicochemical properties have been reaching maturity.8−10 Despite much literature being available on 1,3alkyl imidazolium-based ionic liquids, thus far, the studies on the properties of trialkyl-substituted imidazolium-based ionic liquids are very limited.11−16 © XXXX American Chemical Society

Because of the absence of an acidic proton in the 2 position, the 1,2,3-trialkylated imidazolium cation-based ILs show different features compared with the 1,3-substituted ILs.1 In provious works, 1-butyl-2,3-dimethylimidazolium cations with BF4− (BMMImBF4) and azide (BMMImN3) anions have been investigated and are fully utilized in electrochemical applications.8 The influences of various salts including Na2CO3, Na2SO4, and K2HPO4 on the phase separation of [Emmim][ESO4]−salt ATPSs at different temperatures are investigated by Aliakbar Paraj et al.17 Furthermore, the low dynamic viscosities of imidazolium-based Received: November 16, 2017 Accepted: April 16, 2018

A

DOI: 10.1021/acs.jced.7b01006 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Information of Samples chemical name

CAS registry numbers

n-bromobutane bromopropane potassium thiocyanate 1,2-dimethylimidazole

109-65-9 106-94-5 333-20-0 1739-84-0

ACN [C3mmim][SCN]

1975-5-8

source

initial mole fraction purity

purification method

final mole fraction purity

>0.990 >0.990 0.995 >0.990

distillation distillation precipitation distilled at reduced pressure

0.997 0.998 >0.995 >0.998

>0.990

distillation solvent extraction, vacuum drying solvent extraction, vacuum drying

>0.997 >0.97

Sinopharm (China) Sinopharm (China) Sinopharm (China) Zhejiang doubleport (China) Sinopharm (China)

[C4mmim][SCN] a

>0.97

analysis method GCa GC 1

H NMR

GC, KFb H NMR, IR, EA

1

1

H NMR, IR, EA

Gas−liquid chromatography. bKarl Fischer titration.

Scheme 1. Synthesis Route of ILs (n = 3, 4)

Table 2. Structure Formula of Synthesized Ionic Liquids

ILs with thiocyanate (SCN−) anion have attracted significant attention.18,19 Khare et al.20 report the extraction of Fe from Fe3C using the IL [C2mim][SCN] as a less viscous dispersant. The phase inversion method is used by Xing et al. to investigate the mechanism of asymmetric concave empty cellulose film formation in [C4mim][SCN].21 The high viscosity of ionic liquids in comparison with other organic solvents has been considered as one of the main drawbacks of these fluids in some applications.22 In this respect, the use of a combination of ionic liquids with molecular solvents leads to low viscosity mixtures, which is still useful for a variety of applications. Due to the low viscosity and the ability to dissolve practically most of the important salts, acetonitrile is usually regarded as a key dissolvent among the variety of aprotic dipolar solvents.23 Considering the possible high viscosity result from the trisubstituted imidazoulium cation, an exhaustive study of binary mixtures that consist of ILs and ACN would be advantageous. Herein, we synthesized and characterized two new ionic liquids ([C4mmim][SCN] and [C3mmim][SCN]). For these trialkyl-substituted imidazolium-based ILs, the first study is on the physicochemical properties, such as dynamic viscosity, electrical conductivity, and density. In addition, the significant thermodynamic parameters of the ILs such as the thermal expansion coefficient, standard molar entropy, lattice energy, and interstice model parameters are estimated according to semi-empirical/ empirical methods.24−26 The Vogel−Fulcher−Tamman (VFT) equation and Arrhenius equation are used to describe the temperature dependence of dynamic viscosity and electrical conductivity for two IL binary mixture systems, respectively. Besides, the excess molar volumes of the mixtures, VE, and the deviation of

dynamic viscosities, Δη, are also calculated from 288.15 to 323.15 K over the whole concentration range.

2. EXPERIMENTAL SECTION 2.1. Materials. 1,2-Dimethylimidazole purchased from Zhejiang doubleport Co. Ltd., China, was distilled at reduced pressure before use. n-Bromobutane and bromopropane were purchased from Sinopharm Co., China, followed by distillation before use. Potassium thiocyanate purchased from Sinopharm Co., China, was purified by recrystallization from water. The materials’ purities and sources are summarized in Table 1. 2.2. Preparation of ILs and IL + ACN Binary Systems. The [C3mmim][SCN] and [C4mmim][SCN] were obtained according to Scheme 1. The detailed synthesis process was based on our previously reported method.25,27,28 The ILs were dried under a vacuum at 343.15 K for 48 h, and the water content in the ILs was about 0.03% (ET08, Mettler EasyPlus). Then, the neat ILs were verified by 1H NMR spectroscopy, infrared spectroscopy, and element analysis (see the Supporting Information). Binary system samples were prepared by weighing on a Shanghai JKFA2004N analytical balance with a precision of 0.0001 g. The experimental uncertainties in the mole fractions are less than ±0.0001. The mole fractions of [C3mmim][SCN] in the mixtures are 0.0000, 0.1002, 0.2002, 0.2998, 0.4001, 0.4997, 0.5998, 0.7002, 0.7999, 0.8999, and 1.0000, and those of [C4mmim][SCN] are 0.0000, 0.1001, 0.2004, 0.2999, 0.4003, 0.5001, 0.5999, 0.6999, 0.8002, 0.9002, and 1.0000. The structures of ILs and solvents are listed in Table 2. 2.3. Measurements. Density. Considering the higher temperature will lead to solvent evaporation, the densities were B



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where V is the molar volume of the IL, ρ is the density of pure IL, and T is the temperature. The results from the experimental data are listed in Table 4, which shows [C3mmim][SCN] and [C4mmim][SCN] have similar thermal expansion coefficient values. From the values of density, the molecular volume, Vm, of pure ILs can be calculated by the following equation

continuously and automatically measured using a Mettler Toledo DM45 Delta Range Density Meter from 288.15 to 323.15 K in 5 K increments (Mettler Toledo’s vibrating U-tube technology under atmospheric pressure). Before performing the measurements, the density meter was calibrated with ultrapure dry air and water, and its reproducibility was 10−2 kg·m−3. To avoid gas bubbles entrapped in the measuring cell filled with a sample, the cell was filled carefully to minimize the probability of such an error. On the basis of the relevant experimental conditions, the standard uncertainty is calculated from the repeated experimental data according to the Bessel formula. The standard uncertainty is 0.001 × 103 kg·m−3 for density and 0.01 K for temperature, and the density and the standard uncertainty are listed in Table 3. Dynamic Viscosity. Viscosity measurements were performed by an Anton Paar Lovis 2000M viscometer. The viscosity range of the standard solution is 0.03162−1.13100 Pa·s over the temperature range from 288.15 to 323.15 K at 5 K intervals. The viscosities were measured using different combinations of ball/ capillary of different diameters, which allow a wide range of viscosity test. The relative standard uncertainty is 0.005 for dynamic viscosity and 0.01 K for the temperature. The viscosity of the ILs is listed in Table 3. Electrical Conductivity. The electrical conductivity of the mixtures and neat ILs was measured with a Mettler Toledo SG conductivity meter operating with the InLab738 conductivity electrode (nominal 5.7 × 10−4 m−1 ± 20% cell constant). It was calibrated with the aqueous KCl solution under 0.1 MPa in the temperature range 288.15−323.15 K. For temperature-dependent measurements, a water bath was used to control the temperature. The electrode was placed into the samples at a prefixed temperature. The electrode needed to be stable in the system for 5 min before making measurements. During the course of the experiment, nitrogen was continuously introduced to maintain an anhydrous environment and the stirrer was continuously rotated in the mixing system to keep the system uniform. The relative standard uncertainty of the electrical conductivity is estimated to be 0.05. The electrical conductivities of the ILs are listed in Table 3. Surface Tensions. The surface tensions were measured by a tensiometer (BZY-101 type produced by Shanghai Fangrui instrument Co Ltd.). The BZY-101 meter employs the Wilhemy plate principle; i.e., the maximum tensile force competing with the surface tension is measured when the bottom edge is parallel to the interface and just touches it. First, the surface tension of saturated ultrapure liquid water was measured from 288.15 to 323.15 ± 0.02 K, and the values are in good agreement with the literature.29 The standard uncertainty of the surface tension is 10−4 N·m−1.

Vm = M /(N ·ρ)

where M is the molar mass, ρ is the density, and N is Avogadro’s constant. The calculated values of Vm at 298.15 K for [C3mmim][SCN] and [C4mmim][SCN] are 2.996 × 10−30 and 3.255 × 10−30 m3, respectively. The reported Vm values of [C3mim][SCN] and [C4mim][SCN] are 2.808 × 10−30 and 3.064 × 10−30 m3, respectively.32 It is easy to find that the molecular volumes of the trialkyl-substituted imidazolium-based ILs are larger than those mentioned above. Taking into account the methylation at the 2 position of the cation ring, the Vm values of [C3mmim][SCN] and [C4mmim][SCN] present a reasonable increase. In terms of Glasser’s theory,26 the standard molar entropy, S0, and the lattice energy, UPOT, of the two ILs at 298.15 K can be estimated by the following equations S 0(298.15 K)/J·K−1·mol−1 = 1246.5(Vm/m3) + 29.5

(3)

UPOT(298.15 K)/103 J ·mol−1 = 1981.2(ρ /M )1/3 + 103.8 (4)

where Vm is the molecular volume, M is the molar mass, and ρ is the density at 298.15 K. The calculated standard molar entropy and lattice energy of [C3mmim][SCN] and [C4mmim][SCN] are tabulated in Table 4. The lattice energies of these two ionic liquids are even lower than the lowest lattice energy of molten salts, fused CsI at 298.15 K,29 whose lattice energy is 613 kJ·mol−1. The low lattice energy is one of the underlying reasons of forming thiocyanate ionic liquid at room temperature according to Krossing and Slattery.33 3.2. Interstice Model for the ILs. For neat ILs, several theories have been put forward to describe the structural and transport properties of pure ILs.34−37 Herein, a simple interstice model24,27 is employed for the selected ILs. According to the same procedure of the hole model of molten salt, the expression of the calculation of interstice volume, v, is obtained on the basis of classical statistical mechanics24,25,37 v = 0.6791(k bT /γ )3/2

(5)

where kb is the Boltzmann constant, T is the temperature, and γ is the surface tension of ILs at 298.15 K. The γ values of [C3mmim][SCN] and [C4mmim][SCN] are 4.88 × 10−2 and 4.48 × 10−2 N·m−1, respectively, and the v values of the ILs are listed in Table 5. The volume of the ionic liquid, V, consists of the inherent volume, Vi, and the total volume of all of the interstices, ∑v = 2NAv, that is,

3. RESULTS AND DISCUSSION 3.1. Estimation of Volumetric Properties of ILs. The density is easy to measure in the experiment and has good reproducibility. Furthermore, some significant unmeasurable physicochemical properties like the thermal expansion coefficient, α, molecular volume, Vm, standard molar entropy, S0, and lattice energy, UPOT, can be estimated on the basis of the experimental density. By comparison, the densities of [C3mmim][SCN] and [C4mmim][SCN] (Figure 1) are about 0.88 and 0.81% higher than that of 1,3-alkyl-substituted-based IL with the same anion, respectively.32 According to the definition of the thermal expansion coefficient, the value of α at 298.15 K can be calculated by the following equation 1 ⎛ ∂V ⎞ 1 ⎛ ∂ρ ⎞ α= ⎜ ⎟=− ⎜ ⎟ V ⎝ ∂T ⎠ ρ ⎝ ∂T ⎠

(2)

V = Vi + 2NAv

(6)

If the expansion of the ionic liquid volume only results from the expansion of the interstices with the increasing temperature, the calculation expression of α is derived from the interstice model: α=

1 ⎛⎜ ∂V ⎞⎟ 3Nν = V ⎝ ∂T ⎠ P VT

(7)

The values of α(cal) for the ILs are calculated from eq 7. Obviously, the calculated values are in good accordance with the

(1) C



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Table 3. Density (ρ), Electrical Conductivity (σ), and Dynamic Viscosity (η) of ILs and IL + ACN Binary Systems at T = 288.15−323.15 K, p = 0.1 MPaa [C3mmim][SCN] + ACN xIL T (K) 288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15 T (K) 288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15 T (K) 288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15 xIL T (K) 288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15 T (K) 288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15 T (K) 288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15

0.00000 0.78758 0.78189 0.77652 0.77112 0.76583 0.76036 0.75514 0.74944

0.376 0.357 0.339 0.324 0.309 0.295 0.283 0.272 0.00000

ref

0.1002

0.78204b 0.77666 0.77124 0.76578 0.76029

0.342c 0.328 0.313

0.2002

0.2998

0.88448 0.88024 0.87609 0.87155 0.86737 0.86296 0.85859 0.85424

0.94875 0.94516 0.94145 0.93788 0.93426 0.93069 0.92710 0.92356

5.17 5.50 5.83 6.16 6.49 6.81 7.13 7.45

4.31 4.67 5.05 5.43 5.83 6.22 6.61 7.01

7.694 5.454 3.864 2.697 1.998 1.461 1.077 0.775

16.21 11.9 8.717 6.468 4.904 3.715 2.907 2.285

0.1001

0.2004

0.4001

0.4997

ρ (103 kg·m−3) 0.99605 1.02884 1.05244 0.99252 1.02575 1.04928 0.98889 1.02271 1.04639 0.98524 1.01965 1.04341 0.98165 1.01647 1.04037 0.97811 1.01336 1.03738 0.97443 1.01020 1.03436 0.97089 1.00699 1.03123 σ (S·m−1) 3.45 2.35 1.205 3.84 2.64 1.460 4.27 2.98 1.716 4.71 3.36 2.011 5.16 3.77 2.353 5.62 4.18 2.711 6.10 4.61 3.109 6.58 5.05 3.520 η (10−3 Pa·s) 29.71 51.08 81.84 22.12 37.64 58.62 16.33 27.66 42.09 12.26 20.36 30.78 9.381 15.33 22.87 7.289 11.81 17.46 5.635 9.215 13.52 4.456 7.216 10.53 [C4mmim][SCN] + ACN 0.2999

0.4003

0.5001

0.78758 0.78189 0.77652 0.77112 0.76583 0.76036 0.75514 0.74944

0.376 0.357 0.339 0.324 0.309 0.295 0.283 0.272

0.88899 0.88519 0.88136 0.87750 0.87364 0.86975 0.86595 0.86209

0.95131 0.94802 0.94460 0.94134 0.93814 0.93472 0.93141 0.92798

0.99507 0.99190 0.98857 0.98532 0.98211 0.97872 0.97535 0.97217

4.72 5.01 5.31 5.61 5.92 6.23 6.53 6.83

4.01 4.34 4.69 5.03 5.36 5.70 6.03 6.37

3.35 3.71 4.05 4.42 4.79 5.15 5.52 5.89

16.94 11.74 8.229 5.854 4.393 3.257 2.458 1.882

38.93 27.08 18.85 12.95 9.306 6.633 4.722 3.578

67.12 46.77 32.07 22.58 16.16 11.34 8.162 5.904

0.7002

0.7999

0.8999

1.00000

1.06726 1.06444 1.06168 1.05877 1.05591 1.05306 1.05024 1.04739

1.07784 1.07511 1.0722 1.06941 1.06665 1.06386 1.06096 1.06000

1.08572 1.08311 1.08057 1.07779 1.07533 1.07265 1.06997 1.07000

1.09378 1.09097 1.08808 1.08529 1.08259 1.07986 1.07703 1.07433

1.09981 1.09675 1.09367 1.09061 1.08757 1.08455 1.08154 1.07854

0.95 1.16 1.40 1.67 1.98 2.31 2.67 3.08

0.685 0.883 1.08 1.32 1.59 1.88 2.22 2.60

0.496 0.639 0.789 0.973 1.18 1.42 1.69 2.00

0.378 0.478 0.589 0.720 0.874 1.06 1.26 1.50

0.255 0.361 0.459 0.583 0.733 0.905 1.10 1.33

120.8 85.72 60.63 44.13 32.68 24.53 18.99 14.68

166.5 117.1 82.01 59.49 43.59 32.94 25.5 19.99

215 150.3 105 76.35 55.98 42.28 32.82 25.88

264.8 183.5 128.8 93.37 69.61 53.18 41.20 33.37

316.5 215.8 151.9 110.1 83.42 64.78 50.96 41.55

0.5999

0.6999

0.8002

0.9002

1.00000

1.05073 1.04816 1.04566 1.04317 1.04079 1.03830 1.03583 1.03337

1.06295 1.06042 1.05790 1.05517 1.05269 1.05010 1.04760 1.04521

1.06826 1.06614 1.06384 1.06175 1.05956 1.05726 1.05502 1.05282

1.07599 1.07356 1.07137 1.06894 1.06657 1.06430 1.06187 1.05962

1.08420 1.08111 1.07820 1.07518 1.07216 1.06915 1.06616 1.06320

0.599 0.728 0.891 1.06 1.26 1.48 1.73 2.01

0.429 0.531 0.654 0.795 0.960 1.16 1.38 1.63

0.358 0.458 0.570 0.697 0.853 1.03 1.23 1.46

0.240 0.316 0.390 0.497 0.610 0.749 0.913 1.10

0.106 0.153 0.217 0.293 0.386 0.496 0.627 0.774

193.9 134.8 93.70 66.62 47.89 35.42 26.33 19.96

249.1 172.9 119.9 85.89 62.82 46.81 35.55 27.68

310.4 214.7 148.9 106.9 78.98 59.49 46.09 36.89

377.8 260.4 181.0 130.3 97.33 73.79 57.94 46.83

452.7 311.3 218.0 157.9 118.9 90.46 72.04 57.11

−3

ρ (10 kg·m ) 1.02663 1.03863 1.02400 1.03616 1.02127 1.03349 1.01859 1.03079 1.01592 1.02806 1.01321 1.02543 1.01057 1.02269 1.00790 1.02014 σ (S·m−1) 1.19 0.765 1.45 0.919 1.71 1.12 2.01 1.32 2.34 1.56 2.67 1.81 3.03 2.07 3.40 2.37 η (10−3 Pa·s) 102.7 145.4 71.58 100.9 49.45 69.90 34.51 49.24 24.59 34.95 17.39 25.45 12.95 18.62 9.491 13.67 3

0.5998

a Standard uncertainties are u(xIL) = 0.0001, u(T) = 0.01 K, u(p) = 10 kPa, and u(ρ) = 0.001 × 103 kg·m−3. The relative standard uncertainties are ur(σ) = 0.05 and ur(η) = 0.005. bReference 30. cReference 31.

D



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Figure 1. Plots of density, ρ, vs temperature, T, for the binary systems: (a) [C3mmim][SCN] + ACN; (b) [C4mmim][SCN] + ACN. xIL ≈ (blue circles) 1.0000; (green stars) 0.9000; (pink circles) 0.8000; (navy blue diamonds) 0.7000; (olive green rightward-pointing triangles) 0.6000; (magenta leftwardpointing triangles) 0.5000; (teal downward-pointing triangles) 0.4000; (blue upward-pointing triangles) 0.3000; (red circles) 0.2000; (black squares) 0.1000.

Table 4. Estimated Values of Volumetric Properties of ILs at T = 298.15 K ILs

α (10−4 K−1)

Vm (10−10 m3)

S0 (J·K−1·mol−1)

UPOT (105 J·mol−1)

[C3mmim][SCN] [C4mmim][SCN]

5.56 5.56

2.9960 3.2550

403.04 435.23

4.5439 4.4484

Table 5. Interstice Parameters of ILs at T = 298.15 K

a

ILs

v (10−50 m3)

∑v [10−5 m3 (formula unit)−1]

α(cal) (10−4 K−1)

α(exp) (10−4 K−1)

∑v/V (%)

[C3mmim][SCN] [C4mmim][SCN] [C3mim][SCN] [C4mim][SCN]

1.64 1.66 1.61 1.78

2.0 2.0 1.94 2.15

5.58 5.14 5.80 5.90

5.56 5.56 5.70 5.50

11.1 10.2 11.5a 11.6a

Reference 32.

electrical conductivity intensively increases with the addition of ACN. This result should be from the change of the viscous status of IL by the dilution of solvent, which is similar to most IL + solvent binary systems.40 As is shown, the fitting correlation coefficients are all >0.9996, which indicates that the VFT equation is appropriate to depict the effect of temperature on the electrical conductivity of the mixed binary system. The relations between the viscosity of [C3mmim][SCN]/[C4 mmim][SCN] + ACN binary systems and the temperature of each concentration are presented in Figure 2b and d according to the VFT equation. It can be found that the η values of the binary mixtures decrease with increasing temperature and the addition of ACN. The fitting correlation coefficients are all >0.9996, indicating that the VFT equation can be proper for describing the effect of temperature on the viscosities of the ILs binary systems. In order to further explore the relationship between conductivity/ viscosity and temperature comparatively, an empirical equation derived from ln η/σ against T−1 will be employed according to the Arrhenius equation41

corresponding experimental values. For the majority of materials, the interstice fraction of the volume expansion is about 10− 15%.38 The interstice fraction values, ∑v/V, are listed in Table 5, and the values of [C3mmim][SCN] and [C4mmim][SCN] imply that the interstice model is appropriate to describe these ILs. 3.3. Transport Properties of ILs and Binary Systems. The electrical conductivity and dynamic viscosity are usually considered the most important transport properties to evaluate ILs for applications involving the use of ILs as solvents and electrolytes.38 From the experimental data (see Table 3), first, for the pure ILs, [C3mmim][SCN] has a lower viscosity and a higher electrical conductivity in comparison with [C4mmim][SCN] at different temperatures due to the additional van der Waals interactions caused by the introduction of additional −CH2− units to the imidazolium cation.9 Compared to 1,3-alkyl-substitutedbased ILs with a [SCN] anion, the pure [C3mmim][SCN] or [C4mmim][SCN] presents lower electrical conductivity and higher dynamic viscosities.32 Then, the temperature dependences of electrical conductivities or dynamic viscosities of the binary systems of [C3mmim][SCN]/[C4 mmim][SCN] with ACN in the temperature range from 288.15 to 323.15 K can be expressed by the Vogel−Fulcher− Tamman (VFT) equation39 D = D0 exp[−B /(T − T0)]

′ − Ea /(RT ) ln D = ln D∞

(9)

where D is the electrical conductivity or dynamic viscosity, D′∞ is the empirical constant, R is the gas constant, and Ea is the activation energy for dynamic viscous flow or for electrical conductivity. The fitted results are listed in Table 7 and graphically presented in Figure 3. Herein, the temperature dependences of electrical conductivity or dynamic viscosity for both neat ILs and their mixtures with ACN, in the temperature range from 288.15 to 323.15 K, obey the Arrhenius law. However, from the comparison of correlation coefficients, it is notable that the VFT equation should be better than the Arrhenius equation for describing the variation tendency of temperature on the dynamic viscosities and electrical conductivities of IL.

(8)

where D is the electrical conductivity or dynamic viscosity, D0 represents the infinite electrical conductivity or dynamic viscosity of a system at an extreme temperature, B has a temperature unit and relates to the activation energy of the charge carrier’s motion, and T0 is the “ideal” glassy transition temperature of the liquid. The fitted results are listed in Table 6. From Figure 2a and c, when the temperature increases, the electrical conductivity of each concentration (xIL from 0 to 1) increases as well. Also, the E



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Table 6. VFT Parameters, Correlation Coefficients (R2), and Relative Errors of the IL + ACN Binary Systems [C3mmim][SCN] + ACN σ (S·m−1) −1

η (Pa·s)

xIL

σ0 (S·m )

B (K)

T0 (K)

R

0.1002 0.2002 0.2998 0.4001 0.4997 0.5998 0.7002 0.7999 0.8999 1.0000

36.26 64.23 94.86 231.9 357.4 435.4 440.7 0.921 5673 350.4

295.29 429.57 478.06 794.59 859.09 903.12 880.08 1196.3 2019.6 868.89

136.57 129.21 143.97 115.42 137.16 140.78 151.75 130.78 78.006 167.32

0.99999 0.99997 0.99998 0.99972 0.99991 0.99997 0.99985 0.99995 0.99994 0.99972

2

relative errors

η0 (10

−9

Pa·s)

0.012 0.0196 0.039 2.8752 0.033 5.7367 0.119 4.6741 0.051 172.27 0.026 254.68 0.055 1240 0.024 4050 0.021 33250 0.035 260590 [C4mmim][SCN]

B (K)

T0 (K)

R2

relative errors

−5384.5 −3733.4 −3844.4 −4080.1 −2436.9 −2358.3 −1858.8 −1552.9 −1032.0 −615.49

16.118 48.013 39.516 36.441 101.74 107.73 130.71 145.46 173.28 201.5

0.99972 0.9999 0.99988 0.99981 0.99991 0.99989 0.99984 0.99986 0.99991 0.99996

0.026 0.032 0.061 0.149 0.156 0.265 0.444 0.519 0.493 0.371

σ (S·m−1) −1

η (Pa·s)

xIL

σ0 (S·m )

B (K)

T0 (K)

R

0.1001 0.2004 0.2999 0.4003 0.5001 0.5999 0.6999 0.8002 0.9002 1

51.472 34.629 42.718 76.399 143.79 10854 8943 1487.2 4892.5 118.34

455.2 276.25 313.13 431.96 662.95 1365.7 2239.8 1443.6 1928.3 620.9

97.699 160.04 165.12 184.34 161.7 106.11 62.994 114.74 93.593 199.69

0.99995 0.99996 0.99996 0.99994 0.99985 0.99995 0.99996 0.99996 0.99986 0.99998

2

relative errors 0.037 0.036 0.033 0.041 0.051 0.021 0.017 0.015 0.023 0.006

η0 (10

−9

Pa·s)

10.062 0.0019 0.0035 0.0124 0.0833 1.1941 103 1462 6445 14321

B (K)

T0 (K)

R2

relative errors

−1887.7 −5966.2 −5936.9 −5498.8 −4697.9 −3631.3 −1988.0 −1256.9 −939.30 −810.24

131.3 9.357 10.337 20.463 40.643 69.457 127.79 162.03 179.91 187.62

0.99992 0.99973 0.99974 0.99978 0.99991 0.99994 0.99989 0.99983 0.99983 0.99992

0.028 0.139 0.216 0.302 0.267 0.32 0.516 0.824 0.991 0.823

Figure 2. VFT equation for electrical conductivity, σ {(a) ([C3mmim][SCN] + ACN); (c) ([C4mmim][SCN] + ACN)}, and dynamic viscosity, η {(b) ([C3mmim][SCN] + ACN); (d) ([C4mmim][SCN] + ACN)}, of binary systems at various molar ratios. xIL ≈ (black squares) 1.0000; (red circles) 0.9000; (blue upward-pointing triangles) 0.8000; (magenta downward-pointing triangles) 0.7000; (green diamonds) 0.6000; (blue leftward-pointing triangles) 0.5000; (purple rightward-pointing triangles) 0.4000; (purple circles) 0.3000; (maroon stars) 0.2000; (gray squares) 0.1000.

3.4. Excess Properties of the IL + ACN Binary Systems. Under atmospheric pressure, the experimental density data of the binary mixture systems obtained in the range from 288.15 to 323.15 K are summarized in Table 3 and Figure 1. It can be readily observed that the densities decrease with the increase of acetonitrile content or temperature. To our knowledge, the excess functions

can express the circumstances of deviation of the binary system from ideal behavior. The excess molar volume (VE) of the IL + ACN mixtures are calculated using the following equation7,42,43 VE = F

⎛x M x1M1 + x 2M 2 xM ⎞ − ⎜⎜ 1 1 + 2 2 ⎟⎟ ρ12 ρ2 ⎠ ⎝ ρ1

(10)



Article

Table 7. Arrhenius Parameters, Correlation Coefficients (R2), and Relative Errors of the IL + ACN Binary Systems [C3mmim][SCN] + ACN σ (S·m−1) −1

−1

η (Pa·s)

xIL

Eσ (10 J·mol )

σ∞ (10 S·m )

R

0.1002 0.2002 0.2998 0.4001 0.4997 0.5998 0.7002 0.7999 0.8999 1.0000

8074.97 10778.1 14308.4 17113.3 23655.4 25987.4 29175.4 30612.3 30360.8 35843.9

0.1512 0.3895 1.3653 2.9755 23.817 49.645 137.96 180.52 122.19 854.63

0.99918 0.99934 0.99902 0.99946 0.99908 0.99907 0.99799 0.99892 0.99974 0.99605

3

3

2

relative error

−1

3

Eη (10 J·mol )

η∞ (10

0.003 −50520.0 0.003 −43554.2 0.005 −42079.9 0.004 −43507.5 0.008 −45463.7 0.009 −46717.1 0.015 −47106.0 0.012 −47045.7 0.006 −46045.3 0.027 −44870.7 [C4mmim][SCN] + ACN

−1

−1

R2

relative error

0.99967 0.9997 0.99984 0.99962 0.99927 0.9992 0.99839 0.99801 0.99667 0.99436

0.012 0.009 0.006 0.01 0.016 0.017 0.024 0.026 0.031 0.040

R2

relative error

0.99921 0.99977 0.9998 0.99987 0.99997 0.99966 0.99873 0.99695 0.99569 0.99589

0.016 0.010 0.008 0.007 0.003 0.011 0.021 0.032 0.037 0.037

η (Pa·s)

xIL

Eσ (10 J·mol )

σ∞ (10 S·m )

R

0.1001 0.2004 0.2999 0.4003 0.5001 0.5999 0.6999 0.8002 0.9002 1.0000

8203.04 10218.5 12445.6 23138.3 25084.9 26760.4 29572.7 30932.9 33454.1 43856.5

0.1452 0.2879 0.6115 19.174 27.41 42.974 98.905 148.07 284.5 10079

0.99972 0.99841 0.9982 0.99703 0.9984 0.99952 0.99992 0.99934 0.99933 0.99538

3

Pa·s)

0.054 2.048 6.964 6.588 4.604 4.018 4.665 6.144 11.33 21.66

σ (S·m−1) 3

−10

2

−1

3

relative error

Eη (10 J·mol )

0.002 0.005 0.006 0.015 0.013 0.007 0.003 0.010 0.010 0.036

−48494.7 −53322.9 −53842.8 −53842.8 −52345.0 −50441.8 −48795.9 −47410.3 −46417.7 −45711.9

η∞ (10

−10

Pa·s)

0.266 0.085 0.118 0.262 0.472 1.373 3.447 7.534 13.73 22.04

Figure 3. Arrhenius equation for electrical conductivity, σ {(a) ([C3mmim][SCN] + ACN); (c) ([C4mmim][SCN] + ACN)}, and dynamic viscosity, η {(b) ([C3mmim][SCN] + ACN); (d) ([C4mmim][SCN] + ACN)}, of binary systems at various molar ratios. xIL ≈ (black squares) 1.0000; (red circles) 0.9000; (blue upward-pointing triangles) 0.8000; (magenta downward-pointing triangles) 0.7000; (green diamonds) 0.6000; (navy blue leftwardpointing triangles) 0.5000; (purple rightward-pointing triangles) 0.4000; (purple circles) 0.3000; (maroon stars) 0.2000; (gray squares) 0.1000.

where ρ12 represents the density of mixtures, x1 and x2 are the mole fractions of the ILs ([C3mmim][SCN] and [C4mmim][SCN]) and ACN, M1 and M2 are the molar masses, and ρ1 and ρ2 are the densities of ILs and ACN, respectively. For the correlation of the

excess molar volume and molar fraction, the Redlich−Kister equation can be used44 4

V E = x1x 2 ∑ Ai (x1 − x 2)i i=0

G

(11) DOI: 10.1021/acs.jced.7b01006 J. Chem. Eng. Data XXXX, XXX, XXX−XXX


Article

Table 8. Excess Molar Volume (VE) of the IL + ACN Binary Systems in the Whole Concentration Range from 288.15 to 323.15 Ka T (K) 288.15 xIL 0.0000 0.1002 0.2002 0.2998 0.4001 0.4997 0.5998 0.7002 0.7999 0.8999 1.0000 xIL 0.0000 0.1001 0.2004 0.2999 0.4003 0.5001 0.5999 0.6999 0.8002 0.9002 1.0000 a

293.15

298.15

303.15

0.0000 −0.496 −1.086 −1.724 −2.228 −2.476 −2.101 −1.431 −0.731 −0.198 0.0000

0.0000 −0.540 −1.137 −1.771 −2.282 −2.526 −2.153 −1.530 −0.829 −0.269 0.0000

0.0000 −1.070 −1.730 −2.369 −2.509 −2.022 −1.495 −1.323 −0.412 −0.058 0.0000

0.0000 −1.187 −1.871 −2.506 −2.758 −2.201 −1.647 −1.467 −0.603 −0.189 0.0000

−6

308.15

313.15

318.15

323.15

0.0000 −0.831 −1.536 −2.120 −2.673 −2.859 −2.580 −1.878 −1.197 −0.574 0.0000

0.0000 −0.934 −1.609 −2.216 −2.766 −3.010 −2.759 −2.032 −1.392 −0.770 0.0000

0.0000 −1.677 −2.494 −3.054 −3.652 −2.897 −2.409 −2.094 −1.416 −0.849 0.0000

0.0000 −1.804 −2.637 −3.200 −3.958 −3.072 −2.577 −2.255 −1.589 −0.999 0.0000

−1

V (10 m ·mol of [C3mmim][SCN] + ACN) 0.0000 0.0000 0.0000 0.0000 −0.598 −0.628 −0.682 −0.772 −1.192 −1.258 −1.344 −1.416 −1.825 −1.880 −1.970 −2.039 −2.361 −2.449 −2.541 −2.601 −2.600 −2.664 −2.710 −2.785 −2.231 −2.310 −2.381 −2.484 −1.593 −1.692 −1.763 −1.837 −0.932 −1.006 −1.093 −1.141 −0.381 −0.398 −0.461 −0.495 0.0000 0.0000 0.0000 0.0000 VE (10−6 m3·mol−1 of [C4mmim][SCN] + ACN) 0.0000 0.0000 0.0000 0.0000 −1.281 −1.380 −1.474 −1.579 −1.980 −2.111 −2.244 −2.370 −2.605 −2.722 −2.840 −2.952 −2.966 −3.051 −3.253 −3.469 −2.332 −2.472 −2.608 −2.763 −1.782 −1.934 −2.099 −2.256 −1.585 −1.690 −1.830 −1.958 −0.739 −0.925 −1.096 −1.254 −0.330 −0.450 −0.582 −0.731 0.0000 0.0000 0.0000 0.0000 E

3

The standard uncertainty is u(VE) = ±10−8 m3·mol−1.

Table 9. Fitted Coefficients (Ai) and Standard Deviations (SD) of the R−K Equation Correlated to the Excess Molar Volumes (VE) for the Binary Systems T (K)

A0 (10−6 m3·mol−1)

A1 (10−6 m3·mol−1)

288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15

−9.629 −9.826 −10.13 −10.42 −10.67 −10.99 −11.30 −11.87

1.513 1.292 1.323 1.115 1.296 1.016 1.251 0.743

288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15

−9.0136 −9.6686 −10.2065 −10.7643 −11.3485 −11.972 −12.5453 −13.2389

9.0234 9.0417 9.0712 9.1324 9.055 9.0777 8.9646 8.9674

A2 (10−6 m3·mol−1)

[C3mmim][SCN] + ACN 12.70 11.86 11.74 11.14 10.24 10.24 9.847 9.678 [C4mmim][SCN] + ACN 4.6477 4.0198 3.8727 3.1501 2.4355 2.2875 1.7668 1.3526

where x1 and x2 are the mole fractions. Ai is an adjustable parameter from 288.15 to 323.15 K determined using the least-squares method. The experimental values are given in Table 8, along with the standard deviation, SD, defined as follows45,48 ⎡ n (V E − V E ) 2 ⎤1/2 cal exp ⎥ SD = ⎢∑ ⎢ ⎥ ( − ) n p ⎣ i=1 ⎦

A3 (10−6 m3·mol−1)

A4 (10−6 m3·mol−1)

SD (10−6 m3·mol−1)

0.908 0.899 0.221 0.645 0.217 1.319 1.041 0.840

−0.534 −0.510 −0.641 −0.549 −0.508 −0.586 −0.640 −0.858

0.15 0.13 0.12 0.14 0.13 0.14 0.16 0.21

−4.7118 −5.1037 −5.6401 −6.1711 −6.4788 −7.003 −7.1333 −7.4603

0.0121 −0.0661 −0.2188 −0.2728 −0.3243 −0.4842 −0.5559 −0.6862

0.26 0.26 0.27 0.27 0.27 0.29 0.31 0.33

dependence of the excess properties of the binary mixtures [C3mmim][SCN] + ACN and [C4mmim][SCN] + ACN at temperatures from 288.15 to 323.15 K. The VE values for both binary systems ([C3mmim][SCN] + ACN and [C4mmim][SCN] + ACN) are all negative over the whole composition range at all investigated temperatures (Figure 4), and the absolute values of excess molar volumes increase slightly with an increase of temperature from 288.15 to 323.15 K. The minima in VE are observed at around xIL ≈ 0.5 for [C3mmim][SCN] + ACN and xIL ≈ 0.4 for [C4mmim][SCN] + ACN at all investigated temperatures. It can be assumed

(12)

where n is the number of experimental data and p is the number of parameters. The results (Table 9) show that the R−K equation with four parameters is suitable to estimate the concentration H



Article

Figure 4. Plot of excess molar volumes, VE, of the binary systems (a) [C3mmim][SCN] + ACN and (b) [C4mmim][SCN] + ACN in the whole concentration range at different temperatures. T = (black squares) 288.15 K; (red circles) 293.15 K; (blue triangles) 298.15 K; (teal triangles) 303.15 K; (magenta triangles) 308.15 K; (olive green triangles) 313.15 K; (navy blue diamonds) 318.15 K; and (maroon circles) 323.15 K.

Figure 5. Plot of dynamic viscosity deviations, Δη, of the binary systems (a) [C3mmim][SCN] + ACN and (b) [C4mmim][SCN] + ACN in the whole concentration range at different temperatures. T = (black squares) 288.15 K; (red circles) 293.15 K; (blue upward-pointing triangles) 298.15 K; (magenta downward-pointing triangles) 303.15 K; (green diamonds) 308.15 K; (navy blue leftward-pointing triangles) 313.15 K; (maroon stars) 318.15 K; and (gray squares) 323.15 K.

Table 10. Fitted Coefficients (Ai) and Standard Deviations (SD) of the R−K Equation Correlated to the Dynamic Viscosity Deviation (Δη) for the IL + ACN Binary Systems T (K)

A0 (10−6 m3·mol−1)

A1 (10−6 m3·mol−1)

288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15

−305.1 −196.3 −135.3 −97.02 −75.20 −59.97 −47.91 −41.34

71.14 55.15 30.23 19.61 5.730 −1.852 −2.769 −7.783

288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15

−325.8 −219.4 −156.8 −118.8 −97.53 −79.23 −69.36 −59.39

10.90 13.79 9.115 6.937 −1.999 −0.203 −6.696 −7.132

A2 (10−6 m3·mol−1)

[C3mmim][SCN] + ACN 99.53 74.88 41.25 28.43 11.83 2.546 −1.832 −2.445 [C4mmim][SCN] + ACN 2.382 1.497 −6.516 −4.420 2.231 5.954 5.681 17.79

A3 (10−6 m3·mol−1)

SD (10−6 m3·mol−1)

−64.71 −22.66 −7.083 1.281 2.738 4.248 0.313 6.910

0.43 0.25 0.12 0.13 0.13 0.09 0.08 0.10

−28.05 −22.14 −30.62 −28.96 −17.58 −17.40 −8.781 6.579

0.14 0.09 0.13 0.19 0.24 0.12 0.17 0.14

Further, the deviation of the dynamic viscosity, Δη, is calculated using the following equation47

that more efficient packing and/or attractive interactions occur upon mixing the ILs with ACN.7,46 This negative trend is similar to that of many binary systems (IL + organic solvent),6,7,46 which suggests (1) the interstices in the IL provide space for additional solvent molecules and (2) the number of solvent molecules and the temperature are both key factors for the micropacking and interactions in the binary system.

Δη = η − (x1η1 + x 2η2)

(13)

where x1 and x2 are the mole fractions of the ILs and ACN and η, η1, and η2 are the dynamic viscosities of the binary systems, ILs, and ACN, respectively. Then, Figure 5 shows the deviations from ideality with the change of the IL mole fraction, xIL, at each I



Article

measured temperature. It can be seen from Figure 5 that all Δη values are negative. The values of Δη decrease with the increase of temperature. It is found that the minima deviation of dynamic viscosity is at xIL ≈ 0.5 for each temperature. For the two similar systems, the minima of their viscosity deviations are almost the same. The trends of Δη are obtained by Redlich−Kister’s polynomial fittings of the third order, and the fitted parameters are provided in Table 10, together with the standard deviations, SD, and the values of SD are within the acceptable range.48 The results show the temperature strongly influences the viscosity deviations, but the observed compositions at the minimum in viscosity deviations are found to be almost constant and independent of temperature. Furthermore, the negative Δη values can be explained by the fact that the strong dipole interaction is dominant in these mixtures.49

structures of imidazolium-based ionic liquids. J. Phys. Chem. B 2010, 114, 9201−9208. (2) Lukoshko, E.; Mutelet, F.; Domanska, U. Experimental and theoretically study of interaction between organic compounds and tricyanomethanide based ionic liquids. J. Chem. Thermodyn. 2015, 85, 49−56. (3) Shirota, H.; Mandai, T.; Fukazawa, H.; Kato, T. Comparison between dicationic and monocationic ionic liquids: liquid density, thermal properties, surface tension, and shear viscosity. J. Chem. Eng. Data 2011, 56, 2453−2459. (4) Olivier-Bourbigou, H.; Magna, L.; Morvan, D. Ionic liquids and catalysis: Recent progress from knowledge to applications. Appl. Catal., A 2010, 373, 1−56. (5) Chandran, A.; Prakash, K.; Senapati, S. Self-assembled inverted micelles stabilize ionic liquid domains in supercritical CO2. J. Am. Chem. Soc. 2010, 132, 12511−12516. (6) Ciocirlan, O.; Croitoru, O.; Iulian, O. Densities and viscosities for binary mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid with molecular solvents. J. Chem. Eng. Data 2011, 56, 1526−1534. (7) Aliotta, F.; Ponterio, R. C.; Saija, F.; Salvato, G.; Triolo, A. Excess thermodynamic properties in mixtures of a representative roomtemperature ionic liquid and acetonitrile. J. Phys. Chem. B 2007, 111, 10202−10207. (8) Andriyko, Y. O.; Reischl, W.; Nauer, G. E. Trialkyl-substituted imidazolium-based ionic liquids for electrochemical applications: basic physicochemical properties. J. Chem. Eng. Data 2009, 54, 855−860. (9) Bonhote, P.; Dias, A. P.; Papageorgiou, N.; Kalyanasundaram, K.; Grätzel, M. Hydrophobic, highly conductive ambient-temperature molten salts. Inorg. Chem. 1996, 35, 1168−1178. (10) McEwen, A. B.; Ngo, H. L.; LeCompte, K.; Goldman, J. L. Electrochemical properties of imidazolium salt electrolytes for electrochemical capacitor applications. J. Electrochem. Soc. 1999, 146, 1687− 1695. (11) Awad, W. H.; Gilman, J. W.; Nyden, M. Thermal degradation studies of alkyl-imidazolium salts and their application in nanocomposites. Thermochim. Acta 2004, 409, 3−11. (12) Fredlake, C. P.; Crosthwaite, J. M.; Hert, D. G. Thermophysical properties of imidazolium-based ionic liquids. J. Chem. Eng. Data 2004, 49, 954−964. (13) Bou Malham, I.; Letellier, P.; Mayaffre, A.; Turmine, M. Part I: Thermodynamic analysis of volumetric properties of concentrated aqueous solutions of 1-butyl-3-methylimidazolium tetrafluoroborate, 1butyl-2, 3-dimethylimidazolium tetrafluoroborate, and ethylammonium nitrate based on pseudo-lattice theory. J. Chem. Thermodyn. 2007, 39, 1132−1143. (14) Bou Malham, I.; Turmine, M. Viscosities and refractive indices of binary mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-2, 3-dimethylimidazolium tetrafluoroborate with water at 298 K. J. Chem. Thermodyn. 2008, 40, 718−723. (15) Gardas, R. L.; Freire, M. G.; Carvalho, P. J. High-pressure densities and derived thermodynamic properties of imidazolium-based ionic liquids. J. Chem. Eng. Data 2007, 52, 80−88. (16) Okoturo, O. O.; VanderNoot, T. J. Temperature dependence of viscosity for room temperature ionic liquids. J. Electroanal. Chem. 2004, 568, 167−181. (17) Paraj, A.; Haghtalab, A.; Mokhtarani, B. [1-Ethyl-2, 3-dimethylimidazolium][ethylsulfate]-based aqueous two phase systems: New experimental data and modeling. Fluid Phase Equilib. 2014, 382, 212− 218. (18) Domańska, U.; Laskowska, M. Effect of temperature and composition on the density and viscosity of binary mixtures of ionic liquid with alcohols. J. Solution Chem. 2009, 38, 779−799. (19) Domańska, U.; Królikowska, M. Density and viscosity of binary mixtures of thiocyanate ionic liquids + water as a function of temperature. J. Solution Chem. 2012, 41, 1422−1445. (20) Khare, V.; Kraupner, A.; Mantion, A.; Jelicic, A. Stable iron carbide nanoparticle dispersions in [Emim][SCN] and [Emim][N(CN)2] ionic liquids. Langmuir 2010, 26, 10600−10605.

4. CONCLUSION Two new trialkyl-substituted imidazolium-based ILs, [C3mmim][SCN] and [C4mmim][SCN], were synthesized and characterized. The binary mixture systems composed of IL and acetonitrile were prepared by weighing. The densities, conductivities, and viscosities of two binary mixtures for [C3mmim][SCN] + ACN and [C4mmim][SCN] + ACN were measured over the entire composition range from 288.15 to 323.15 K at 5 K intervals. A series of thermodynamic parameters of the pure [C3mmim][SCN] and [C4 mmim][SCN] are estimated by empirical or semiempirical equations on the basis of the experimental data. The results show that density and viscosity present a decreasing trend with increasing temperature or addition of ACN. However, the electrical conductivities increase with the rise of temperature. The VFT equation is also employed to describe the temperature dependences of viscosity and conductivity. The excess molar volume VE and viscosity deviations Δη are calculated and fitted well with the Redlich−Kister polynomial equation. The negative values over the whole concentration range indicate efficient packing and/or attractive interactions occur upon mixing the IL with ACN.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.7b01006. FTIR, 1H NMR, and EA for ILs in this work (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: + 86 18604968816. Fax: + 86 416 3400708. ORCID

Qingguo Zhang: 0000-0002-0172-9579 Funding

This work was financially supported by The Nature Science Foundation of Liaoning Province (No. 201602016), The Doctoral Fund of Liaoning Province of China (No. 201601347), Program for Liaoning Excellent Talents in University, China (LJQ2015099), and National Nature Science Foundation of China (No. 21373002, No. 21503020). Notes

The authors declare no competing financial interest.

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REFERENCES

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