Specific Conductivities and Viscosities of 0.1LiNO3 + 0.9

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Specific Conductivities and Viscosities of 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] as Functions of Mole Fraction, x, and Temperature Sanchayita Rajkhowa,† Anuradha Das,‡ Sekh Mahiuddin,*,† and Ranjit Biswas*,‡ †

Materials Science Division, CSIR-North East Institute of Science and Technology, Jorhat-785006, Assam, India Department of Chemical, Biological and Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake City, Kolkata 700 098, India

‡

S Supporting Information *

ABSTRACT: Specific conductivities and viscosities of molten mixtures of lithium nitrate, acetamide, and urea with the composition, 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2], have been measured as functions of mole fraction of acetamide (0.40 ≤ x ≤ 0.75) and temperature (283.15 ≤ T/K ≤ 353.15). The Vogel−Tammann−Fulcher (VTF) equation describes reasonably well the experimental specific conductivity and viscosity data. A minimum in the conductivity is then explained in terms of rigid complex formation between Li+ and acetamide molecules. Subsequently, the mixture composition dependence of the B parameter (obtained via fit to VTF equation) has been related to this solution structural modification.

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acetamide is highly polar solvent and exhibits “water-like” properties and many reports appeared since its exploration as a nonaqueous solvent.22 A variety of physicochemical properties of molten (acetamide + salt) and (urea + salt) mixtures have already been reported,22−24,27−30,32−40 and studies of solute− solvent coupling in these media have also emerged recently.41−43 Acetamide has −CH3 and −NH2 connected to a carbonyl functional group, whereas urea has two −NH2 groups that are connected to carbonyl group. As a result, both have different physicochemical properties. The phase diagram of CH3CONH2+CO(NH2)2 exhibits an interesting eutectic point at ∼46 °C and 0.62 mole fraction of CH3CONH2 in spite of their high melting points (∼ 80 °C for acetamide and ∼133 °C for urea).44 As a result this nonaqueous solvent mixture is a good candidate for many applications. However, studies using the mixtures of acetamide and urea as a solvent are rather limited and thus require exploration for possible use. In this paper we report the specific conductivity and viscosity of ternary system 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] as functions of mole fraction of acetamide, x, and temperature. Following the phase behavior of molten (acetamide + urea) mixtures,44 we restrict the composition of acetamide in the range (40 to 75) mol % due to limitations of solubility of LiNO3 in this binary mixture and temperature control.

INTRODUCTION Physicochemical properties of a variety of electrolytes and nonelectrolytes in aqueous medium and aqueous−nonaqueous solvents mixtures have been reported and documented since mid 1800s. Results of electrolytes in water and nonaqueous solvents played a critical role for understanding solution behaviors, their possible practical applications and the subsequent development of theories encompassing dilute, intermediate, and concentrated regions.1−16 On the other hand, mixed solvent systems were studied primarily for understanding the preferential solvation aspect and explore the possible use of solvent mixtures in extraction processes.3,17−21 Among the nonaqueous solvents, besides common organic liquid solvents, acetamide and urea display interesting solvent properties since both polar and nonpolar solutes are easily soluble in them.22−26 Interestingly, the eutectic temperatures of molten (acetamide + salt) or (urea + salt) mixtures are much lower than the melting point of the individual components. As a result, these mixtures are often termed as “molten supercooled mixtures”.23,27−30 Remarkable solvent properties of molten acetamide coupled with wider liquidus temperature range and lower vapor pressure of these molten mixtures has made them as potential alternative media for chemical reactions in industrial applications. The polarization-resolved mid-infrared pump−probe spectroscopic findings of highly concentrated aqueous solution of urea suggested that the orientational dynamics of majority water molecules are like that of in pure bulk water and only few water molecules form complexes with urea (immobilized by urea) resulting in slower orientational dynamics.31 Molten © 2012 American Chemical Society

Received: June 7, 2012 Accepted: November 5, 2012 Published: November 27, 2012 3467

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Table 1. Values of Density (kg·m−3) of 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] and 0.20LiNO3 + 0.80[0.65xCH3CONH2 + 0.35CO(NH2)2] Systems as Functions of Mole Fraction of CH3CONH2, x, and Temperaturea 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] T/K 283.15 293.15 303.15 313.15 323.15 328.15 333.15 338.15 343.15

x = 0.40

1233.7 1226.9 1219.5 1216.1 1212.6 1208.9 1205.1

± ± ± ± ± ± ±

1.4 1.2 1.3 0.1 0.5 0.1 1.1

x = 0.50 1220.1 1215.6 1208.5 1201.7 1194.4 1190.9 1187.3 1183.5 1180.1

± ± ± ± ± ± ± ± ±

0.3 0.7 1.0 1.1 0.9 1.1 1.0 1.2 0.7

x = 0.55

x = 0.60

x = 0.625

1209.8 ± 0.8 1197.4 ± 1.2 1201.9 ± 0.7 1190.1 ± 1.1 1195.4 ± 1.0 1183.1 ± 1.1 1188.1 ± 1.1 1176.1 ± 1.1 1180.5 ± 1.3 1169.1 ± 1.0 1178.1 ± 1.3 1165.6 ± 1.0 1174.7 ± 1.2 1162.1 ± 0.9 1171.8 ± 0.6 1158.4 ± 0.6 1167.7 ± 1.0 1154.9 ± 0.7 0.20LiNO3 + 0.80[0.65CH3CONH2

293.15 303.15 313.15 323.15 328.15 333.15 338.15 343.15

x = 0.65

1193.3 ± 0.5 1185.5 ± 1.0 1178.2 ± 0.9 1171.0 ± 0.9 1163.8 ± 0.8 1159.9 ± 0.6 1156.4 ± 0.8 1152.8 ± 0.8 1149.0 ± 0.7 + 0.35CO(NH2)2]

1188.1 1181.3 1174.2 1165.8 1159.3 1155.8 1152.1 1148.3 1144.8

± ± ± ± ± ± ± ± ±

1.0 1.0 1.0 1.1 1.2 1.1 0.9 1.0 0.9

1235.5 1228.2 1221.0 1214.0 1210.4 1206.9 1203.3 1199.7

± ± ± ± ± ± ± ±

1.0 0.6 0.6 0.9 1.0 0.6 0.8 1.0

x = 0.70 1169.1 1161.7 1154.4 1147.2 1143.5 1139.8 1136.1 1132.4

± ± ± ± ± ± ± ±

0.6 0.5 0.5 0.5 0.5 0.6 0.6 0.5

x = 0.75 1158.8 1151.4 1144.0 1137.0 1133.1 1129.4 1125.7 1122.0

± ± ± ± ± ± ± ±

1.3 1.3 1.0 1.2 1.3 1.3 1.0 1.0

Measurements were carried out at atmospheric pressure (0.1 MPa). Uncertainties in temperature and composition (mole fraction) were ± 0.05 % (∼0.02 K) and ± 0.0001, respectively. The prefix (numerical values and x) of the system, 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] represents the mole fraction. a

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EXPERIMENTAL SECTION Materials and Methods. Anhydrous LiNO3 (> 98 %, Merck, Germany) and acetamide (99 %, Alfa Aesar, UK) were kept in a vacuum desiccator over P2O5 for a week and urea (99.5 %, Rankem, India) was kept in a vacuum desiccator over fused CaCl2 for ∼24 h and subsequently used without further purification. The specific conductivities, κ, of all the solutions were measured at 1 kHz field frequency using platinized platinum electrodes of cell constants = 1.05 and 1.08 cm−1 employing four-terminal connections to Precision Component Analyzer 6440A (Wayne Kerr, UK). The cell constants were determined by using a 0.1 mol·kg−1 KCl(aq) solution at different temperatures45 and were rechecked by measuring conductivities of some standard electrolyte solutions. The viscosity, η, of all of the solutions was measured with the help of a Schott-Geräte AVS310 unit and an Ubbelohde viscometer. Viscometers of different viscometer constants [(0.03039, 0.1126, 0.3127, and 0.5337) mm2·s−2] were used to measure the efflux times at different concentrations and temperatures. At each temperature, five efflux times were averaged to calculate the dynamic viscosity. Viscosities and specific conductivity values were reproduced within ± 5 % of the mean values with uncertainties of ± 0.008 Pa·s and ± 0.00024 S·cm−1, respectively. Densities required to convert the kinematic viscosities to dynamic ones were measured in triplicate by using a density-cum-sound velocity analyzer DSA5000 (Anton Paar, Austria). The uncertainties in each measured densities are noted in Table 1. A thermostat type Schott-Geräte CT1450 or Julabo F32 HP was used to maintain a constant temperature of the solutions with ± 0.05 % uncertainty.

are shown in Figure 1S (Supporting Information). The temperature dependence of specific conductivity and viscosity exhibits non-Arrhenius behavior, and the deviations from the linearity in the lnY vs 1/T were ∼7.5 % and ∼19 %, respectively (Figures 2S and 3S, Supporting Information). Such temperature dependence is typical for highly concentrated solutions. The specific conductivity and viscosity data were then fitted to the Vogel−Tammann−Fulcher (VTF) equation46−48 of the form ⎤ ⎡ ±B Y Y (κ , η) = AY exp⎢ ⎥ ⎣ (T − T0Y ) ⎦

(1)

where Y refers to either specific conductivity or viscosity, AY and BY are the adjustable parameters, and T0Y is the ideal glass transition temperature. For the specific conductivity the parameter, Bκ carries a negative value. The best-fitted values of the VTF parameters are given in Table 1S (Supporting Information). It is interesting to note that the variations of T0κ and T0η as a function of mole fraction of acetamide, x, are not consistent with each other. In the case of specific conductivity, T0κ is nearly constant for the composition range, 0.60 ≤ xCH3CONH2 ≤ 0.75, but for 0.40 ≤ xCH3CONH2 ≤ 0.60, T0κ decreases with the increase of mole fraction of acetamide, x. In contrast, T0η is roughly constant within the mole fraction of acetamide, 0.40 ≤ xCH3CONH2 ≤ 0.75. Such variation or irregular trend of T0κ and T0η vs composition for the same system with common composition is not surprising and reported for the binary and ternary melts in the literature.49−51 In the present systems the experimental temperature range for both specific conductivity and the viscosity are not the same. The reason is that while measuring the time of fall for the viscosity in the lower temperature range the system crystallizes and the temperature range could not be maintained as in the case of specific conductivity measurements. Further, the values of the VTF parameters primarily depend on the magnitude of

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RESULTS AND DISCUSSION Measured densities, specific conductivities, and viscosities of 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] systems are given in Tables 1 to 3, respectively. The density isotherms 3468

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Table 2. Values of Specific Conductivity (S·cm−1) of 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] and 0.20LiNO3 + 0.80[0.65CH3CONH2 + 0.35CO(NH2)2] Systems as Functions of Mole Fraction of CH3CONH2, x, and Temperaturea 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] T/K 283.15 285.15 288.15 290.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15 338.15 343.15 348.15 353.15

x = 0.40

x = 0.50

x = 0.55

0.00312 0.00398

0.00069 0.00101 0.00142 0.00194 0.00250 0.00321 0.00400

0.00030 0.00036 0.00047 0.00056 0.00071 0.00103 0.00146 0.00195 0.00254 0.00317 0.00401

0.00582 0.00688 0.00802 0.00925 0.01050

0.00582 0.00687 0.00803 0.00925 0.01050

0.00577 0.00681 0.00804 0.00915 0.01040 0.20LiNO3 +

x = 0.60

x = 0.625

0.00031 0.00031 0.00037 0.00048 0.00048 0.00057 0.00057 0.00076 0.00072 0.00103 0.00103 0.00150 0.00142 0.00189 0.00257 0.00246 0.00310 0.00402 0.00387 0.00487 0.00576 0.00564 0.00685 0.00665 0.00801 0.00776 0.00916 0.00893 0.01040 0.01020 0.80[0.65CH3CONH2 + 0.35CO(NH2)2]

283.15 288.15 293.15 298.15 303.15 313.15 323.15 333.15 338.15 343.15 353.15

x = 0.65

x = 0.70

x = 0.75

0.00033 0.00039 0.00051 0.00060 0.00076 0.00109 0.00151 0.00199 0.00260 0.00326 0.00407 0.00481 0.00587 0.00688 0.00804 0.00922 0.01050

0.00034 0.00041 0.00053 0.00062 0.00079 0.00113 0.00153 0.00203 0.00267 0.00332 0.00411

0.00035 0.00042 0.00055 0.00063 0.00080 0.00116 0.00154 0.00209 0.00264 0.00333 0.00419

0.00600 0.00702 0.00819 0.00939 0.01070

0.00605 0.00703 0.00816 0.00937 0.01080

0.00015 0.00026 0.00041 0.00062 0.00090 0.00169 0.00284 0.00440 0.00534 0.00634 0.00873

a

Measurements were carried out at atmospheric pressure (0.1 MPa). Uncertainties in specific conductivity, temperature, and composition (mole fraction) were ± 0.00024 S·cm−1, ± 0.05 % (∼ 0.02 K), and ± 0.0001, respectively. The prefix (numerical values and x) of the system, 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2], represents the mole fraction.

the deviation from the linearity in the ln Y vs 1/T plots (Figures 2S and 3S, Supporting Information) and, therefore, the irregular variation of the VTF parameters with composition in the present system is obvious. Alternatively, we adopted the procedure of Moynihan et al. for explaining the variation of the VTF parameters with composition.49 According to this method, data fitting to the VTF equation is done by keeping the empirical facts that the BY parameter is almost composition-independent and the values of T0κ are roughly equal to T0η. In the present systems the specific conductivities were measured in a wider temperature range in comparison to viscosity (for reasons discussed above). Therefore, we comment that the values of the VTF parameters for the specific conductivity are reasonably reliable, and viscosity data were refitted to the VTF equation keeping T0κ ≈ T0η and B0κ ≈ B0η. In addition, the fitting parameters, Bκ and Bη, were chosen considering the reported BY values for the molten (0.22LiNO3 + 0.78CH3CONH2) mixture.52 The values of the VTF parameters as obtained by this approach are listed in Table 4. It is interesting to note that BY increases as urea is gradually replaced by acetamide in the melt for the range, 0.4 ≤ xCH3CONH2 ≤ 0.625, and then becomes nearly constant (Figure 1). This result suggests that BY is probably related to the

solution structure and may be explained by considering the parameters involved in B as follows53

B=

ΔμSc* k ΔCp

(2)

where Δμ is the free energy barrier per mole of particles hindering the cooperative rearrangement, S*c is the critical configurational entropy, k is the Boltzmann constant, and ΔCp is the difference between the liquid and glass heat capacities. For increasing the numerical value of the BY parameter in eq 2, values of Δμ and S*c should increase, and ΔCp should decrease. On the other hand, for constant numerical value of the BY parameter in eq 2, effects of Δμ and Sc* should be counterbalanced by ΔCp with the change in composition. We do not have numerical values for the parameters of eq 2 for a clear explanation for the linear increase and constancy of the BY parameter as a function of xCH3CONH2 (Figure 1). However, we presume that the above explanations prevail in the present system for explaining the variation of BY parameter with xCH3CONH2. Further Li+ at higher concentrations forms stronger complexes with molten acetamide,52 which is also responsible for the higher numerical value of the By parameters. To examine this view we have also measured the specific conductivity and 3469

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Table 3. Values of Viscosity (Pa·s) of 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] and 0.20LiNO3 + 0.80[0.65CH3CONH2 + 0.35CO(NH2)2] Systems as Functions of Mole Fraction of CH3CONH2, x, and Temperaturea 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] T/K 283.15 285.15 288.15 290.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15 328.15 333.15 338.15 343.15 348.15 353.15

x = 0.40

0.0279 0.0228 0.0188 0.0156 0.0132 0.0114

x = 0.50

0.2805 0.2150 0.1477 0.0998 0.0740 0.0553 0.0422 0.0320 0.0263 0.0207 0.0176 0.0143 0.0126 0.0108

x = 0.55

x = 0.60

x = 0.625

x = 0.65

x = 0.70

x = 0.75

0.4496 0.3623 0.2771 0.2316 0.1818 0.1238 0.0832 0.0638 0.0469 0.0365 0.0283 0.0228 0.0185 0.0153 0.0129 0.0109 0.0093

0.1860 0.1194 0.0833 0.0605 0.0447 0.0350 0.0274 0.0221 0.0179 0.0148 0.0124 0.0106 0.0091

0.1540 0.1060

0.5048 0.5242 0.4155 0.3835 0.4249 0.3220 0.2913 0.3165 0.2678 0.2439 0.2634 0.2064 0.1899 0.2024 0.1379 0.1268 0.1344 0.0976 0.0870 0.0948 0.0690 0.0673 0.0523 0.0481 0.0507 0.0398 0.0370 0.0308 0.0292 0.0299 0.0249 0.0225 0.0238 0.0200 0.0186 0.0193 0.0167 0.0152 0.0159 0.0140 0.0129 0.0133 0.0119 0.0109 0.0113 0.0103 0.0094 0.0098 0.20LiNO3 + 0.80[0.65CH3CONH2 + 0.35CO(NH2)2]

293.15 298.15 303.15 313.15 323.15 333.15 338.15 343.15 348.15 353.15

0.0553 0.0339 0.0261 0.0212 0.0172 0.0144 0.0121 0.0103 0.0087

0.6706 0.4234 0.2899 0.1440 0.0785 0.0485 0.0390 0.0317 0.0263 0.0220

a

Measurements were carried out at atmospheric pressure (0.1 MPa). Uncertainties in viscosity, temperature, and composition (mole fraction) were ± 0.008 Pa·s, ± 0.05 % (∼ 0.02 K), and ± 0.0001, respectively. The prefix (numerical values and x) of the system, 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2], represents the mole fraction.

Table 4. Least-Squares-Fitted Values of the Parameter of eq 1 for the Specific Conductivity (S·cm−1) and Viscosity (Pa·s) of 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] Taking T0κ ≈ T0η and B0κ ≈ B0ηa AY/S·cm−1 (Pa·s)

x

a

± ± ± ± ± ± ± ±

0.0290 0.0132 0.0250 0.0664 0.0016 0.0269 0.0151 0.0407

(3.79·10−4 (3.33·10−4 (3.33·10−4 (2.34·10−4 (2.21·10−4 (2.31·10−4 (1.42·10−4 (2.08·10−4

0.40 0.50 0.55 0.60 0.625 0.65 0.70 0.75

0.2215 0.3019 0.3187 0.3793 0.3982 0.3731 0.3702 0.3998

0.65

0.5760 ± 0.0236 (2.45·10−4

BY/K

T0Y/K

0.09·10−4) 376.0 ± 28.1 (411.0 ± 4.9) 229.7 ± 4.0 0.18·10−4) 449.7 ± 9.7 (481.1 ± 4.1) 219.2 ± 1.2 0.27·10−4) 467.4 ± 17.4 (510.9 ± 6.1) 216.5 ± 2.0 0.14·10−4) 506.9 ± 40.7 (540.8 ± 9.5) 212.1 ± 4.6 0.07·10−4) 511.6 ± 30.9 (550.3 ± 5.2) 211.5 ± 1.4 0.11·10−4) 506.1 ± 16.9 (545.6 ± 7.5) 211.4 ± 1.9 0.07·10−4) 501.2 ± 9.5 (583.2 ± 9.3) 211.7 ± 1.1 0.07·10−4) 520.1 ± 24.1 (540.8 ± 6.2) 209.3 ± 2.7 0.2LiNO3 + 0.8[xCH3CONH2 + (1 − x)CO(NH2)2], x = 0.65 ± 0.13·10−4) 595.6 ± 9.8 (650.5 ± 10.3) 211.0 ± 1.0 ± ± ± ± ± ± ± ±

Values of the VTF (eq 1) parameters for viscosities are within the parentheses. Std. Dev. =

(∑n1(Yexptl

(232.7 (218.8 (213.7 (212.2 (212.4 (211.2 (211.9 (211.4

std. dev. in Y ± ± ± ± ± ± ± ±

2.27·10−5 1.41·10−5 3.04·10−5 6.58·10−5 7.10·10−6 2.76·10−5 1.53·10−5 3.70·10−5

0.6) 0.7) 1.0) 0.7) 0.5) 0.6) 0.8) 0.6)

(1.50·10−4) (1.85·10−3) (4.62·10−3) (2.36·10−3) (1.60·10−3) (2.20·10−3) (1.01·10−3) (5.65·10−4)

8.64·10−6 (2.80·10−3)

(211.0 ± 0.7)

− Ycalc) /n − 3) . 2

1/2

− x)CO(NH2)2] and 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] with x = 0.65 systems are very similar, but BY values of 0.2LiNO3 + 0.8[xCH3CONH2 + (1 − x)CO(NH2)2], x = 0.65 is higher than the corresponding 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] with x = 0.65 system. The specific conductivity and viscosity isotherms of 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] systems at 333.15 K are shown in Figure 2. The viscosity linearly decreases with gradual replacement of urea by acetamide. In contrast, the variation of specific conductivity isotherm is

the viscosity of 0.2LiNO3 + 0.8[xCH3CONH2 + (1 − x)CO(NH2)2], x = 0.65, and values of the VTF parameters are shown in Table 4. For this system, specific conductivities and viscosities are respectively ∼1.2 to 2 times lower and ∼2.4 to 3.6 times higher (depending on the temperature range) than the corresponding 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] with x = 0.65 system. The results indicate that the increase in Li+ in the solvent mixture influences the viscosity of the system (Table 3). The estimated ideal glass transition temperatures of 0.2LiNO3 + 0.8[xCH3CONH2 + (1 3470

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composition dependence of conductivity may vary from that of viscosity.54

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ASSOCIATED CONTENT

S Supporting Information *

Best-fitted values of the VTF parameters of eq 1, the density isotherms, and the Arrhenius plots for specific conductivity and viscosity. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (S.M.) and [email protected] (R.B.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Authors are thankful to the Directors, S N Bose National Centre for Basic Sciences, Kolkata, India and CSIR-North East Institute of Science & Technology, Jorhat, India for support and encouragement. S.R. and A.D. are grateful respectively to DST and UGC, New Delhi for granting fellowship. Authors are grateful to anonymous reviewers for valuable suggestions that improved the quality of the manuscript.

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Figure 1. Variation of BY and T0Y parameters of eq 1 (a) specific conductivity and (b) viscosity as a function of mole fraction of CH 3 CONH 2 , x. Open symbols represent 0.1LiNO 3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] melts, and solid symbols represent 0.2LiNO3 + 0.8[xCH3CONH2 + (1 − x)CO(NH2)2], x = 0.65 system. The lines are drawn as a guide to the eye.

REFERENCES

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Figure 2. Specific conductivity (closed circles) and viscosity (closed squares) isotherms as a function of mole fraction of CH3CONH2, x at 333.15 K for 0.1LiNO3 + 0.9[xCH3CONH2 + (1 − x)CO(NH2)2] melts. The lines are drawn as a guide to the eye.

different, showing nonmonotonic composition dependence. It first decreases up to xCH3CONH2 = 0.625 and then increases upon further increase of x in the mixture. Observing the phase diagram of acetamide−urea binary systems, the eutectic is formed at ∼60 mol % of acetamide.44 The extent of complexation is probably the most pronounced at this composition, leading to a minimum in the ion conductivity. Since ions can use nonhydrodynamic modes (such as jump) in addition to viscosity-governed route for its mobility, the 3471

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