Micelle Formation of Protic Ionic Liquids in Aqueous Solution

Article abstract of DOI:10.1021/acs.jced.7b01053

The ionic liquids potentialities to organize themselves in aqueous solution and produce aggregates were analyzed through the conductivity technique and after using a new mathematical model based on stochastic theories, to indicate the linearity change moment; it was possible to analyze the presence of these aggregates. It earns interest at science of colloids and interfacial chemistry due to the recognized ability of certain surfactant ionic liquids to reduce the surface tension of aqueous solutions and to aggregate in the form of micelles, even at low concentrations, allowing their use as stabilizing or destabilizing agents in homogeneous polymerization in water/oil emulsions. Within this context, this work aims to verify the possible micellar properties of the ionic liquids. Critical micellar concentration values for ions ammonium alkyl carboxylates were obtained. It was also shown that the CMC is directly related to the lipophilic groups of the cation and entropic factors.

Full text of DOI:10.1021/acs.jced.7b01053

Article
pubs.acs.org/jced
Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Micelle Formation of Protic Ionic Liquids in Aqueous Solution
Dheiver Santos*
Department of Engineering, Tiradentes University Center (UNIT), Av. Comendador Gustavo Paiva, 5017, Cruz das Almas, Maceio,
Alagoas, CEP: 57038-00, Brazil
́
Department of Engineering, Maurício de Nassau University Center (UNINASSAU), R. Jose
CEP: 57051-565, Brazil
́ ́
de Alencar, 511 - Farol, Maceio, Alagoas,
S
* Supporting Information
ABSTRACT: The ionic liquids potentialities to organize themselves in
aqueous solution and produce aggregates were analyzed through the
conductivity technique and after using a new mathematical model based
on stochastic theories, to indicate the linearity change moment; it was
possible to analyze the presence of these aggregates. It earns interest at
science of colloids and interfacial chemistry due to the recognized ability
of certain surfactant ionic liquids to reduce the surface tension of aqueous
solutions and to aggregate in the form of micelles, even at low concen-
trations, allowing their use as stabilizing or destabilizing agents in homo-
geneous polymerization in water/oil emulsions. Within this context, this
work aims to verify the possible micellar properties of the ionic liquids. Critical micellar concentration values for ions ammonium
alkyl carboxylates were obtained. It was also shown that the CMC is directly related to the lipophilic groups of the cation and
entropic factors.
were consistent with the formation of micelles. Santos et al.4
observed the formation of aggregates via ionic liquids based on
1. INTRODUCTION
Ionic liquids (ILs) are organic salts that are liquid at room tem-
perature.1−6 These have been widely used as solvents, contribute
the conductivity measurement with anion stearate. Therefore,
the self-aggregation study and surface interactions are essential in
to the environment as they do not give off gas responsible for the
understanding properties, technical applications, and the envi-
ronmental fate of ILs.
greenhouse effect, and can be used in organic reactions, chro-
matography, and homogeneous catalysis. The number of appli-
cations for ILs continues to grow exponentially.4,7 In the latest
years, the aggregate properties and interfacial behavior of amphi-
philic ionic liquids have received a lot of attention because of
their potential. In recent years, ILs have been used in polymer
science, mainly as polymerization media in several types of
polymerization processes.8−11 The work of Guerrero-Sanchez10
revealed that aqueous solutions of ionic liquids can be used as a
means of reactions and produce better control of particle size
than some processes currently used in the industry. The authors
reinforce that ionic liquids based on ammonium cations can act
as stabilizers of colloidal suspensions. Therefore, as scientific
advances continue, it is necessary to investigate micellar prop-
erties of other ionic liquids in aqueous solution.12−14
The literature reviews relate a few works to the determination
of micellar properties of protic ionic liquids. Anouti et al.15
examined aggregate behavior of the length of alkyl chains (n = C5
to C8) for conductivity measured with a tensiometer and found
that the critical micelle concentration (cmc) decreases for the
families studied (pyrrolydynium/imidazolium) by increasing
the length of the chain. This behavior has been interpreted,
according to the authors, in terms of a balance between the forces
that overcome the van der Waals and favor the formation of
aggregates. In a previous work of our group, Alvarez et al.16 via
NMR spectra determined self-diffusion coefficients of ionic
liquid 2-hydroxy ethylammonium oleate, the results of which
Santos et al.17 was showed that the electric conductivity of
aqueous solutions of protic ionic liquids based on stearates
decreases with the increase of anion and the side-chain size, the
authors reveal that this behavior is related to the fact that the
medium becomes more organic which causes the conductivity to
decrease. In other works, it has frequently been observed that
ionic liquids are used as inhibitors of gas hydrates.18,19 Alcantara
et al.20 reported the vapor−liquid equilibrium data of systems
composed by CO2 + protic ionic liquid to predict the carbon
dioxide activity coefficients. They suggested that the boiling point
elevations depend on the interaction forces between carbon dioxide
and ionic liquids because of the anionic nature.
This work aims to check the possible micellar properties of
protic ionic liquids formed from a Brønsted acid−base reaction
and propose a new mathematical method to verify the ionic
liquids self-aggregation. The influences of structural variations
in their properties are important to modulate the properties
and therefore their applications. The ionic liquids tested are
hydroxyethyl amine, N-methyl ethanolamine cations, bis(2-
hydroxyethyl) amine, and C2 to C5 anions based on carboxylic
Received: December 2, 2017
Accepted: March 19, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.jced.7b01053
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Article
Table 1. Chemicals Used in the Present Study
a
CAS number
chemical name
supplier
purity (mol %)
water (ppm)
verification method
141-43-5
90367-28-5
109-83-1
64-19-7
2-hydroxyethylamine
Sigma-Aldrich
Sigma-Aldrich
Sigma-Aldrich
Vetec
>98
>98
>98
>99
>99
>99
>99
>98
>98
>98
>98
>98
>98
>98
>98
>98
>98
>98
>98
NMR, FT-IR
NMR, FT-IR
NMR, FT-IR
NMR, FT-IR
NMR, FT-IR
NMR, FT-IR
NMR, FT-IR
NMR
bis(2-hydroxyethyl)amine
N-methylethanolamine
acetic acid
79-09-4
propionic acid
Vetec
107-92-6
109-52-4
N-butyric acid
Vetec
pentanoic acid
Vetec
2-(hydroxy)ethylammonium acetate 2-HEAA
2-(hydroxy)ethylammonium propionate 2-HEAB
2-(hydroxy)ethylammonium butanoate 2-HEAPr
2-(Hydroxy)ethylammonium pentanoate 2-HEAP
Bis(2-hydroxyethyl)ammonium acetate m-2HEAA
Bis(2-hydroxyethyl)ammonium propionate m-2HEAPr
Bis(2-hydroxyethyl)ammonium butanoate m-2HEAB
Bis(2-hydroxyethyl)ammonium pentanoate m-2HEAP
N-methyl-2-hydroxy-ethylammonium acetate BHEAA
N-methyl-2-hydroxy-ethylammonium propionate BHEAPr
N-methyl-2-hydroxy-ethylammonium butanoate BHEAB
N-methyl-2-hydroxy-ethylammonium pentanoate BHEAP
synthesized
synthesized
synthesized
synthesized
synthesized
synthesized
synthesized
synthesized
synthesized
synthesized
synthesized
synthesized
≤1000
≤1000
≤1000
≤1000
≤1000
≤1000
≤1000
≤1000
≤1000
≤1000
≤1000
≤1000
NMR
NMR
NMR
NMR
NMR
NMR
NMR
NMR
NMR
NMR
NMR
a
NMR, nuclear magnetic resonance; FT-IR, Fourier transform infrared spectroscopy.
acids (acetate, propionate, and butyrate pentanoate) forming
12 different ionic liquids in aqueous solution.
was then washed with deionized water to remove any adhering
material and dried to preserve the conductivity before the next
measurement. Deionized pure water is a poor electrical con-
ductor with a conductivity of 0.013572 mS/cm.
2. EXPERIMENTAL SECTION
2.3. New Mathematical Method. The critical micelle
concentrations (cmc) in IL/water mixtures were determined by a
nonlinear parameter estimation of a proposed unified equation.
The proposed fitting equation, F(x) was derived from two arbi-
trary linear equations, f1(x) and f 2(x), and a smooth regu-
larization function, g(x).
2.1. Preparation of Protic Ionic Liquids. The hydrox-
yethyl amine, N-methyl ethanolamine and bis(2-hydroxyethyl)
amine were obtained from Aldrich with 0.98% mass fraction of
purity; the organic acids were obtained from Vetec with a purity
greater than 0.99%. These compounds were used as received.
The ILs used in this work were prepared from stoichiometric
amounts of amines and organic acids using the methodology
detailed in the work by Alvarez et al.21 These substances were
used with no further purification, and further material character-
istics are given in Table 1.
f1(x) = ax + b
(1)
f 2(x) = c(x − d) + f1(d) = cx + (ad + b − cd)
(2)
⎡
⎤
⎥
The amine was placed in a glass flask fitted with a condenser, a
temperature sensor PT-100 temperature control, and a funnel.
The apparatus was fitted in an ice bath to keep the reaction
temperature below 283.15 K, since the reaction is exothermic.
The organic acid was added drop by drop on the balloon with a
bar magnet at a 450 rpm agitation rate, applied in order to
improve the shock between the reagents, allowing the reaction to
complete. The reaction was allowed to rest for 24 h at room
temperature in order to obtain a viscous liquid. The reaction is a
simple acid−base neutralization of Brønsted forming an ionic
liquid. Then, under high vacuum (10−4 Pa) the ILs were totally
dried, and the structure was confirmed by FTIR. The water
content was determined with a Karl Fisher coulometer, and a
mass fraction of water less than 1% was indicated.
⎡
⎢
⎤
⎥
(x − d)
(x − d)2 + (xmax − xmin) (ξ)2
⎢
g(x) = .5 + .5
⎢
⎥
⎦
2
⎢
⎣
⎥
⎦
⎣
(3)
This regularization function assumes values close to zero, for
values of x lower than d, and assumes values closes to 1, for values
of x greater than d. The proposed fitting equation is then
assembled in the following manner.
F(x) = f1(x)[1 − g(x)] + f 2(x)[g(x)]
= ax + b + (c − a)(x − d)[g(x)]
(4)
In other works,22−24 the CMC determination was done by inde-
pendently fitting two linear equations to selected experimental
points, with two parameters being estimated in each regression,
hence, with a total of four parameters being estimated. Linear
regressions were performed with one set of data in the lower
concentration region, and the other set in the higher concen-
tration region, and the CMC was determined by the interception
value between the two lines.
2.2. Conductivity Measurements. Conductivity measure-
ments were performed with a hand-held mCA-150P manufac-
tured by Tecnopon with a calibrated cell constant of 1.1 cm −1
.
The temperature was monitored by a thermometer; the con-
ductivity cell was first set to zero in air followed by calibration
with a standard solution prior to the sample being measured with
a Tecnopon MS instrumentation solution with 146 mS/cm
conductivity. The temperature of the oven was kept constant at
293 1 K. The solutions molar concentration of ionic liquids
always was corrected to account for the contribution of the pure
solvent present in the ionic liquid prepared. The conductivity cell
This new approach eliminates the subjectivity of selecting
experimental points for different independent linear regression.
All the set of data is utilized in the estimation procedure of
parameters from a single nonlinear equation. The equation
B
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contains four parameters, namely, a which represents the slope of
the lower concentration region, b which represents the measured
variable at zero concentration, c which represents the slope of the
higher concentration region, and d which represents the CMC
value. It should be noted that through this approach, the lower
and higher concentration regions are automatically defined and
remove totally the experimenter subjectivity. In addition, the
parameter b was assumed fixed as the average measured value for
water conductivity at zero IL concentration (0.013572 mS/cm).
Therefore, three parameters were estimated, utilizing data from
both concentration regions simultaneously.
where H is the Hessian matrix, given by
∂2F
obj
Hi,j =
∂αiαj
(8)
In addition, this methodology allows confidence intervals for
the estimated CMC values to be calculated, based on the quality
of the fit. Confidence region intervals are very important for
comparisons between CMC obtained for different ILs or in
different works, as they will define if it can be safely assumed that
different values for the estimated CMC are due to different prop-
erties of the substances, or may just be the result of experimental
fluctuations.
The estimation procedure in this work utilized the least-
squares objective function, by comparison of measured and pre-
dicted conductivity values for different concentrations.
Nexp
F (α) =
(ye − yc(xi, α))2
∑
obj
i
∼
∼
(5)
Figure 2. Conductivity of {BHEAP + water} solutions at 293 K as a
i=1
function of concentration.
where
α
is the set of parameters for estimation, xi is the concen-
∼
Table 2. Critical Micelle Concentration (m/103 mol·kg−1) of
tration measurements, yie is the conductivity measurements, and yic
is calculated conductivities. Nexp stands for number of experimental
points and Npar stands for number of estimated parameters.
Confidence intervals were calculated by performing a t-Student
test, with a 95% level of significance. A consistent estimation for
experimental variance can be inferred from the estimation square
residuals:
Aqueous Solutions of Ionic Liquids, Using New Method to
a
293 K and 0.1 MPa
ionic liquids
2-HEAA
2-HEAPr
2-HEAB
2-HEAP
FH
ST
-
166.8
191.1
212.4
102.6
169.2
253.8
146.2
172.4
188.0
79.6
98.5
F
obj
cmc
+
σy2
=
107.2
N
− Npar
exp
(6)
(7)
-
162.4
191.1
95.6
169.2
148.6
172.4
196.2
BHEB
84.1
98.5
The estimated parameter variance matrix is given by
cmc
+
V = 2σy2H−1
219.8
242.9
112.8
≈
≈
BHEAA
BHEAPr
BHEAP
FH
123.1
-
131.2
155.1
171.1
119.8
141.1
183.2
111.4
117.0
126.2
cmc
+
132.0
139.9
ST
-
120.4
129.9
155.1
105.1
141.1
106.8
117.0
cmc
+
132.0
143.6
180.3
183.1
127.2
m-2HEAA
m-2HEAPr
m-2HEAB
m-2HEAP
FH
-
147.8
180.4
204.1
ST
158.2
177.8
190.1
108.8
123.5
135.9
121.1
139.9
158.8
cmc
+
-
147.3
180.4
213.6
162.5
177.8
193.1
104.6
123.5
142.3
113.1
139.9
166.7
cmc
+
a
Standard uncertainties are u(T) = 1 K, u(p) = 1 kPa, expanded
uncertainties are U(m) = 1.10−3 mol·kg1− (95% level of confidence).
Notation: cmc, critical micellar concentration; , confidence region;
FT − Fisher Test; ST, Student Test.
Figure 1. Conductivity of {m-2HEAPr + water} solutions at 293 K as a
function of concentration.
C
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And finally, limit parameter values are calculated by
for 12 protic ionic liquids based on ammonium cation in mixtures
with water using the proposed method.
αlim = α t‐Student2.5% α
σ
(9)
When an ionic liquid is dissolved in water, the presence of
the hydrophobic part causes a distortion in the water structure,
which increases the free energy of the system. In this result the
entropy system decreases due to the structuring of water mole-
cules around the hydrophobic chain (“hydrophobic hydration”)
and to the reduction in degrees of freedom of the hydrophobic
chain.26−29
However, to minimize the free energy of the system, the
molecules of ionic liquids adsorb in the air/water interface. In ILs
adsorbed, their hydrophobic chains are facing out of the solution
and the hydrophilic groups remain in the aqueous interface. The
energy decreases due to the gain in entropy by releasing the water
of hydration and by the replacement of water molecules by
molecules of ionic liquids on the interface.
Alternatively, they can also suffer other processes in order to
reduce the energy, when the concentration of surfactants in the
solution is increased, the molecules present within the solution
come together forming micelles. As the work to take a surfactant
molecule to the interface is smaller than that corresponding to
one molecule of water, the surfactant presence decreases the
work needed for a larger interfacial area resulting in a reduction of
surface tension.22,30−33
The objective function minimization given was performed by the
particle swarm optimization algorithm (PSO). PSO25 is a heuristic
algorithm, consisting of random evaluations of the objective func-
tion in an given parameter search region, a determinist and a
random weight term for guidance of consecutive evaluations. This
optimization methodology allows the abstention of a more reliable
confidence interval, which is not necessarily symmetrical. All
parameter value sets, which during the stochastic sampling, yield an
objective function with a value lower than a limit, are considered
as a part interval. This limit is calculated from a Fisher test with
N
par and Nexp − Npar degrees of freedom, and, as defined for the
t-Student test, with a 95% level of significance.
⎛
⎝
⎞
⎠
Npar
− Npar
⎜
⎟
⎟
Flimit = F 1 +
Fisher95%
obj
⎜
N
exp
(10)
3. RESULTS AND DISCUSSION
This paper proposes a mathematical method for the objective
determination of CMC values from conductivity experiments and
presents results of determination of critical micelle concentration
Table 3. Conductivity (σ/mS·cm−1) of Ionic Liquids in Aqueous Solutions at Different Concentrations (m/103 mol·kg−1) and
a
Temperatures (T) at Ambient Pressure 0.1 MPa (p)
2HEAA
m-2HEAA
BHEAA
m/103 mol·kg−1
σ/ mS·cm−1
m/103 mol·kg−1
σ/ mS·cm−1
m/103 mol·kg−1
σ/ mS·cm−1
test 1 test 2
test 1
test 2
test 1 test 2
test 1
test 2
test 1 test 2
test 1
test 2
24.10
20.15
39.83
1.38
2.74
1.30
2.62
21.02
41.30
22.29
45.56
1.03
1.89
0.92
1.85
17.97
35.39
15.79
32.69
0.90
1.62
0.77
1.40
2.10
2.90
3.56
5.07
5.61
6.07
6.60
7.05
7.50
7.87
8.33
8.70
8.99
9.42
9.68
9.98
10.29
10.40
10.80
11.07
11.34
11.56
47.96
74.52
57.74
4.00
3.59
64.89
69.82
2.99
2.99
53.69
51.65
2.36
99.82
74.16
5.12
4.50
86.42
92.90
3.80
3.87
71.32
69.43
3.18
126.74
151.85
177.81
202.54
228.46
252.12
275.46
297.71
319.93
340.41
361.46
381.08
400.30
418.42
435.90
452.65
464.20
479.67
494.26
508.55
522.10
535.12
547.31
559.42
570.52
90.15
6.28
5.39
109.98
133.00
156.60
178.40
201.51
223.31
245.90
267.06
288.52
308.34
328.53
347.10
365.82
383.19
400.41
416.33
432.24
447.16
461.75
475.12
488.07
500.53
512.86
524.35
535.54
118.18
144.20
169.99
193.16
217.56
240.35
263.33
285.33
307.58
328.54
349.50
368.90
388.60
406.83
424.79
441.66
458.34
473.78
488.98
503.21
517.22
530.21
543.61
556.07
4.71
4.81
90.23
88.22
3.85
105.73
121.35
135.56
148.47
162.08
174.28
186.74
200.36
215.74
232.55
250.23
269.05
286.75
303.21
318.90
333.66
347.58
360.85
385.54
407.49
427.85
446.31
462.69
477.43
7.37
6.18
5.51
5.74
108.43
126.40
145.84
164.08
180.86
198.35
213.31
230.75
246.03
261.58
276.00
290.42
304.20
317.48
329.84
342.20
354.23
365.43
376.47
386.77
396.73
406.47
415.54
424.48
106.33
125.47
143.33
161.99
179.33
197.19
213.44
230.26
245.78
261.46
276.19
290.92
304.42
317.82
330.25
342.50
354.01
365.45
376.00
4.53
8.47
7.02
6.37
6.64
5.51
9.50
7.75
7.15
7.49
6.12
10.62
11.58
12.32
13.31
14.18
14.87
15.67
16.39
17.15
17.72
18.30
18.66
18.99
19.40
19.92
20.41
20.86
21.28
21.69
22.28
22.67
8.35
7.90
8.22
6.65
9.00
8.70
8.92
7.13
9.58
9.47
9.66
7.62
10.19
10.77
11.42
12.13
12.89
13.68
14.37
14.35
14.80
15.64
16.07
16.13
17.50
18.65
19.29
19.84
20.33
20.77
10.14
10.80
11.41
12.04
12.60
13.17
13.71
14.21
14.64
15.08
15.51
15.94
16.37
16.81
17.25
17.61
17.97
18.26
10.32
11.09
11.61
12.20
12.75
13.31
13.83
14.32
14.73
15.15
15.60
16.07
16.49
16.80
17.03
17.34
17.58
8.04
8.38
8.77
8.61
8.93
9.26
9.57
10.15
10.42
10.71
10.97
11.21
11.45
11.67
11.88
12.10
12.40
12.69
a
Standard uncertainties are u(T) = 1 K, u(p) = 1 kPa, u(σ) = 0.32σ mS·cm−1 (68% level of confidence); expanded uncertainties are U(m) =
1.10−3 mol·kg−1 (95% level of confidence).
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Figures 1 and 2 show the behavior of the ionic conductivity of
the liquid solutions, studied in order to obtain the critical micelle
concentration (CMC) of each binary system. You can see in the
figures the change of ownership with the increased concentration
of N-methyl-2-hydroxyethylammonium propionate {m-2HEAPr}
and bis(2-hydroxyethyl) ammonium pentanoate {B2HEAP},
that point where there is a change in the slope of the line, which is
called the cmc. Details about the proposed method can be seen in
section 3, where the variables and fitted parameters equation
used to represent the conductivity of ionic liquids in aqueous
solution are described in detail. The deviations of the fitting
equation are less than 1%.
Tables 2 to 6 summarize values of concentration in which the
phenomenon (CMC) occurs. This can be realized with ionic
liquids based on carboxylic acids, which would be governed by a
particular structural factor considering the number of carbon
atoms in the chain, methyl, or hydroxyl groups and are not
sufficient for property control. In addition, entropic factors are
highly related to this property, that is, the decrease in entropy due
to the structuring of water molecules around the hydrophobic IL
sector is the most influential factor for the organization.
Perhaps, by structural similarity and similar solubility levels of
the compounds studied, there is the concentration proximity
value on which the phenomenon of critical micelle occurs. It is
important to notice that with the series of ionic liquids in this
work, all feature values with physical meaning, that is, the
estimated parameter d of the proposed model, feature significant
values and never show negative values.
4. CONCLUSION
The ionic liquid micelle formation in water was investigated for
ionic liquids based on the ammonium cation. The conductivity of
ionic liquids solutions with increasing concentration was studied
in this work with a new methodology to determine the CMC
value. Our results indicate that the reduction in the carbonic
chain of anion promotes the process of formation of micelles
due to differences in solubility in the solvent. This work also
shows that the formation of aggregates with protic ionic liquids is
Table 4. Conductivity (σ/mS·cm−1) of Ionic Liquids in Aqueous Solutions at Different Concentrations (m/103 mol·kg−1) and
a
Temperatures (T) at Ambient Pressure 0.1 MPa (p)
2HEAPr
m-2HEAPr
m/103 mol·kg−1
test 1 test 2
BHEAPr
m/103 mol·kg−1
σ/ mS·cm−1
σ/ mS·cm−1
m/103 mol·kg−1
σ/ mS·cm−1
test 1 test 2
test 1
test 2
test 1
test 2
test 1 test 2
test 1
test 2
17.86
22.00
44.47
1.07
1.98
1.16
2.18
19.26
37.49
19.74
37.70
1.09
1.96
1.04
1.92
15.50
31.83
14.87
31.59
0.73
1.39
0.66
1.33
1.95
2.66
3.23
3.78
4.27
4.76
5.23
5.68
6.13
6.54
6.94
7.02
7.21
7.23
7.86
8.14
8.34
8.60
9.06
9.23
9.46
9.67
9.87
10.08
10.30
10.49
10.51
10.70
10.86
10.94
11.11
11.24
34.91
54.16
68.41
3.12
3.38
57.27
57.22
2.96
2.96
48.90
48.81
2.02
72.80
91.26
4.00
4.30
75.96
76.10
3.75
3.65
65.27
64.92
2.77
92.90
113.70
137.34
159.37
182.23
203.82
226.27
247.19
268.04
287.72
307.35
325.08
342.68
359.37
375.54
390.49
405.50
419.47
433.40
446.50
459.06
470.89
482.48
4.85
5.21
95.70
96.17
4.56
4.47
80.46
82.14
3.29
112.15
132.24
150.40
169.20
188.05
206.69
232.80
253.17
272.87
290.49
307.40
323.71
338.79
353.43
366.85
379.83
391.71
403.20
413.77
423.98
535.12
547.31
559.42
570.52
5.74
6.12
114.17
133.49
151.90
170.71
184.51
202.93
220.04
237.48
253.47
269.63
284.96
300.22
314.17
328.23
341.30
353.85
365.80
377.47
388.41
399.18
409.22
419.02
428.27
437.19
445.66
453.91
461.66
469.20
475.88
115.20
135.00
154.25
171.80
189.85
207.12
224.35
240.64
257.11
272.20
287.53
301.87
316.21
329.34
342.40
354.47
365.97
377.44
388.11
398.62
408.30
418.01
427.11
436.10
444.50
452.71
5.28
5.19
97.48
98.89
3.84
6.58
6.95
6.01
5.96
113.58
130.51
146.35
162.24
177.56
193.46
208.08
223.01
237.01
249.95
263.22
275.63
287.91
299.35
310.60
321.05
331.72
341.47
351.11
360.17
369.11
377.42
385.63
393.35
400.86
407.90
414.84
115.88
132.44
149.54
165.12
181.35
196.58
212.07
226.36
240.77
254.17
267.73
280.03
292.24
303.62
314.86
325.46
335.69
345.43
354.99
363.99
372.60
380.78
388.54
395.99
403.18
409.85
416.49
422.72
4.36
7.40
7.80
6.70
6.68
4.87
8.21
8.45
7.37
7.25
5.36
8.97
9.21
7.85
7.98
6.04
9.82
9.91
8.49
8.75
6.48
10.84
11.64
12.39
13.03
13.68
14.26
14.81
15.32
15.79
16.26
16.68
17.06
17.43
17.79
18.16
18.55
18.90
19.25
10.58
11.22
11.84
12.38
12.92
13.41
13.92
14.34
14.77
15.14
15.53
15.87
16.17
16.45
16.72
9.01
9.42
6.90
9.55
9.97
7.27
10.02
10.49
10.91
11.29
11.68
12.05
12.40
12.73
13.04
13.25
13.62
13.89
14.13
14.36
14.58
14.87
15.10
15.35
15.56
15.78
15.94
10.29
10.80
11.25
11.70
11.61
12.26
12.68
13.13
13.50
13.86
14.09
14.37
14.69
14.98
15.27
15.49
15.75
16.02
7.64
7.98
8.29
8.72
9.08
9.33
9.57
9.80
10.01
10.22
10.41
10.60
10.77
10.94
11.09
11.34
11.53
11.74
11.91
12.07
a
Standard uncertainties are u(T) = 1 K, u(p) = 1 kPa, u(σ) = 0.32σ mS·cm−1 (68% level of confidence); expanded uncertainties are U(m) =
1.10−3 mol·kg−1 (95% level of confidence).
E
DOI: 10.1021/acs.jced.7b01053
J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data
Article
Table 5. Conductivity (σ/mS·cm−1) of Ionic Liquids in Aqueous Solutions at Different Concentrations (m/103 mol·kg−1) and
a
Temperatures (T) at Ambient Pressure 0.1 MPa (p)
2HEAB
m-2HEAB
BHEAB
m/103 mol·kg−1
σ/ mS·cm−1
m/103 mol·kg−1
σ/ mS·cm−1
m/103 mol·kg−1
σ/ mS·cm−1
test 1 test 2
test 1
test 2
test 1 test 2
test 1
test 2
test 1 test 2
test 1
test 2
20.70
18.55
35.07
1.07
1.96
0.92
1.63
18.05
35.16
17.98
35.77
0.90
1.66
0.77
1.42
14.43
30.59
16.09
31.61
0.41
0.77
1.15
1.49
1.85
2.32
2.67
2.97
3.28
3.55
3.83
4.08
4.34
4.56
4.78
4.96
5.16
5.28
5.42
5.58
5.72
5.86
6.00
6.11
6.24
6.34
6.46
6.56
0.47
0.84
1.22
1.55
1.89
2.35
2.68
2.98
3.24
3.50
3.72
3.95
4.20
4.40
4.60
4.80
4.98
5.13
5.25
5.40
5.56
5.71
5.83
5.96
6.07
6.19
6.29
6.39
41.50
62.47
56.78
2.95
2.64
53.97
55.31
2.57
2.07
47.18
48.51
82.83
76.51
3.72
3.38
70.90
74.33
3.18
2.84
63.11
64.01
104.87
125.81
147.57
168.07
188.84
208.72
228.41
246.85
265.38
282.46
300.12
316.47
332.65
347.54
362.24
375.81
389.41
402.08
414.42
425.94
437.35
447.96
458.39
468.10
477.53
486.43
494.98
503.24
97.13
4.49
4.10
94.24
94.07
3.89
3.46
80.77
81.76
119.01
140.74
162.84
184.02
205.48
225.13
244.84
262.64
280.94
297.97
315.30
331.00
346.75
361.32
375.94
389.20
402.29
414.48
423.11
434.40
444.92
455.37
465.08
474.59
483.51
492.22
500.51
508.55
516.00
523.07
5.11
4.85
108.51
127.48
145.53
163.81
180.70
198.19
214.40
230.97
246.38
261.59
275.77
289.91
303.18
316.24
328.35
340.24
351.40
362.25
372.56
382.63
391.74
402.17
411.46
420.14
428.43
436.79
444.55
112.20
131.56
149.61
168.30
185.95
203.48
220.28
237.03
252.45
267.89
282.41
297.05
310.60
323.99
332.14
343.83
355.47
366.50
377.36
387.47
397.46
406.84
415.98
424.50
432.96
4.53
4.03
96.98
97.05
5.85
5.63
5.19
4.86
114.60
130.69
147.95
163.76
180.21
195.23
210.60
224.59
238.43
251.38
264.41
276.63
288.65
299.76
311.01
321.44
331.71
341.19
350.50
359.26
367.85
375.81
113.92
129.83
146.40
161.39
177.05
191.79
206.42
220.08
233.62
246.59
259.56
271.16
283.02
294.05
304.81
314.84
324.72
333.97
343.01
351.51
359.87
367.68
6.49
6.37
5.81
5.38
7.11
7.09
6.41
5.77
7.64
7.70
6.96
5.97
8.10
8.34
7.50
6.51
8.57
8.94
8.01
6.94
9.00
9.46
8.70
7.25
9.40
9.94
9.12
7.64
9.82
10.41
10.86
11.22
11.66
12.04
12.32
12.69
12.97
13.24
13.41
13.65
13.87
14.09
14.27
14.46
14.63
14.84
15.03
15.21
15.36
15.52
9.54
7.82
10.20
10.56
10.88
11.21
11.49
11.78
12.04
12.28
12.51
12.75
12.95
13.16
13.34
13.55
13.76
13.95
14.11
9.94
8.21
10.30
10.65
11.00
11.31
11.63
11.91
12.19
12.44
12.67
12.86
13.21
13.50
13.77
14.02
14.27
14.50
8.62
9.08
9.50
9.80
10.02
10.22
10.47
10.46
10.70
10.97
11.17
11.41
11.61
11.82
a
Standard uncertainties are u(T) = 1 K, u(p) = 1 kPa, u(σ) = 0.32σ mS·cm−1 (68% level of confidence); expanded uncertainties are U(m) =
1.10−3 mol·kg−1 (95% level of confidence).
Table 6. Conductivity (σ/mS·cm−1) of Ionic Liquids in Aqueous Solutions at Different Concentrations (m/103 mol·kg−1) and
a
Temperatures (T) at Ambient Pressure 0.1 MPa (p)
2HEAP
m-2HEAP
m/103 mol·kg−1
test 1 test 2
BHEAP
m/103 mol·kg−1
σ/ mS·cm−1
σ/ mS·cm−1
m/103 mol·kg−1
σ/ mS·cm−1
test 1 test 2
test 1
test 2
test 1
test 2
test 1 test 2
test 1
test 2
19.13
19.18
37.81
1.08
1.90
2.60
3.09
3.65
4.12
4.80
5.26
5.78
6.25
6.61
7.01
7.39
0.68
1.26
1.76
2.44
2.96
3.44
3.93
4.39
4.83
5.23
6.64
5.97
6.37
14.62
30.93
17.05
32.18
0.55
1.08
1.61
2.04
2.68
3.12
3.65
4.08
4.49
4.86
5.24
5.26
5.58
0.64
1.16
1.68
2.15
2.79
3.28
3.75
4.20
4.70
5.12
5.57
5.95
6.34
13.96
27.42
11.38
24.31
0.62
1.13
1.65
2.09
2.69
3.10
3.30
4.08
4.45
4.79
5.13
5.44
5.72
0.49
0.98
1.49
1.91
2.38
2.93
3.35
3.75
4.16
4.49
4.85
4.98
5.27
37.18
56.21
58.01
48.74
49.10
42.10
39.23
74.57
77.59
64.76
65.59
55.79
52.24
94.98
99.26
82.67
81.09
60.70
67.05
113.49
133.64
151.97
171.77
189.91
206.68
223.96
240.04
118.75
140.16
159.40
179.61
198.14
217.36
234.78
252.87
99.39
97.93
83.28
80.75
116.98
133.04
148.78
162.95
177.91
191.56
205.78
115.87
132.60
150.73
166.82
183.76
199.44
215.25
96.05
95.53
109.53
122.38
135.85
148.38
160.78
172.66
109.18
123.99
137.24
150.55
163.21
175.86
F
DOI: 10.1021/acs.jced.7b01053
J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data
Article
Table 6. continued
2HEAP
m-2HEAP
m/103 mol·kg−1
test 1 test 2
BHEAP
m/103 mol·kg−1
σ/ mS·cm−1
σ/ mS·cm−1
m/103 mol·kg−1
σ/ mS·cm−1
test 1
test 2
test 1
test 2
test 1
test 2
test 1 test 2
test 1
test 2
256.45
272.04
287.53
301.98
316.49
329.94
343.45
356.08
368.53
379.98
391.41
401.97
412.57
422.09
431.63
440.43
269.72
286.67
302.36
318.08
332.87
347.40
360.82
374.38
386.58
398.76
410.12
421.46
431.79
442.11
451.73
7.76
8.09
6.69
7.04
7.34
7.59
7.86
8.12
8.32
8.55
8.76
8.95
9.17
9.25
9.40
9.57
9.71
219.67
233.65
246.74
259.98
272.31
284.82
296.49
307.92
318.79
339.59
349.42
358.48
367.53
376.02
384.36
392.07
399.74
406.92
444.55
229.72
244.66
258.40
272.12
285.08
297.63
309.60
321.39
332.13
342.81
352.67
362.52
371.63
380.63
389.04
397.26
5.93
6.24
6.55
6.85
7.11
7.39
7.55
7.89
8.11
8.35
8.54
8.76
8.93
9.14
9.25
9.25
9.25
9.73
9.91
6.69
7.06
7.39
7.67
7.95
8.22
8.48
8.74
8.96
9.18
9.40
9.60
9.79
9.99
10.15
10.31
184.40
194.73
205.91
216.36
226.01
235.85
245.09
254.06
262.47
270.31
278.33
285.33
292.90
299.80
306.52
312.88
319.14
324.94
330.68
336.02
341.31
187.86
199.94
211.26
222.56
232.89
242.65
252.30
261.96
270.93
279.69
288.20
296.37
303.97
311.40
318.43
325.48
331.70
337.85
343.66
349.34
354.60
5.97
6.12
6.35
6.56
6.77
6.97
7.09
7.27
7.44
7.60
7.76
7.90
8.04
8.18
8.30
8.42
8.53
8.68
8.80
8.93
10.37
5.51
5.78
6.02
6.20
6.42
6.63
6.82
7.01
7.17
7.35
7.50
7.66
7.81
7.94
8.08
8.19
8.34
8.47
8.58
8.70
8.82
8.44
8.75
9.04
9.30
9.57
9.83
10.10
10.32
10.53
10.73
10.93
11.10
11.30
11.44
a
Standard uncertainties are u(T) = 1 K, u(p) = 1 kPa, u(σ) = 0.32σ mS·cm−1 (68% level of confidence); expanded uncertainties are U(m) =
1.10−3 mol·kg−1 (95% level of confidence).
Ionic Liquids Based on Stearate Anion. Fluid Phase Equilib. 2014, 376,
132−140.
similar to that of other surfactants such as omim cl and SDS.
Consequently, the results are compatible with the possibility of
solvophobic-type interactions within the solvent, being one of
those responsible for the process of self-aggregation along with
entropic and lipophilic factors and when water molecules are
organized along the hydrophobic region of ionic liquids.
(2) Santos, D.; Bamufleh, H. S.; Uslu, H. Prigogine-Flory-Patterson
Evaluation of Systems with Ionic Liquids + Water or Methanol: A Study
of Specific Interactions. J. Mol. Liq. 2018, 253, 23−27.
(3) Pinto, R. R.; Santos, D.; Mattedi, S.; Aznar, M. Density, Refractive
Index, Apparent Volumes and Excess Molar Volumes of Four Protic
Ionic Liquids + Water at T = 298. 15 and 323. 15 K. Braz. J. Chem. Eng.
2014, 32, 671−682.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jced.7b01053.
■
S
(4) Santos, D.; Costa, F.; Franceschi, E.; Santos, A.; Dariva, C.;
Mattedi, S. Synthesis and Physico-Chemical Properties of Two Protic
Ionic Liquids Based on Stearate Anion. Fluid Phase Equilib. 2014, 376,
132−140.
Mathematical model in python and tutorial video (ZIP)
́
(5) Santos, D.; Goes, M.; Franceschi, E.; Santos, A.; Dariva, C.;
Fortuny, M.; Mattedi, S. Phase Equilibria for Binary Systems Containing
Ionic Liquid with Water or Hydrocarbons. Braz. J. Chem. Eng. 2015, 32,
967−974.
AUTHOR INFORMATION
Corresponding Author
*E-mail: dheiver.francisco@souunit.com.br; dheiver.santos@
gmail.com.
■
(6) Santos, D.; Santos, M.; Franceschi, E.; Dariva, C.; Barison, A.;
Mattedi, S. Experimental Density of Ionic Liquids and Thermodynamic
Modeling with Group Contribution Equation of State Based on the
Lattice Fluid Theory. J. Chem. Eng. Data 2016, 61, 348−353.
ORCID
Dheiver Santos: 0000-0002-8599-9436
́
(7) Alvarez, V. H.; Dosil, N.; Gonzalez-Cabaleiro, R.; Mattedi, S.;
Notes
Martin-Pastor, M.; Iglesias, M.; Navaza, J. M. J. M. Brønsted Ionic
Liquids for Sustainable Processes: Synthesis and Physical Properties †. J.
Chem. Eng. Data 2010, 55, 625−632.
The author declares no competing financial interest.
́
(8) Biedro, T.; Kubisa, P. Ionic Liquids as Reaction Media for
ACKNOWLEDGMENTS
The author wishes to express his sincere gratitude to his
colleagues at the Tiradentes University Center and Mauricio de
■
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́
Nassau University Center, Professors Iuri Segtovich (UFRJ),
Silvana Mattedi (UFBA) and Edilson Ponciano (UNIT) for all
their support.
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DOI: 10.1021/acs.jced.7b01053
J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data
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DOI: 10.1021/acs.jced.7b01053
J. Chem. Eng. Data XXXX, XXX, XXX−XXX