Salt effect on mixed micelle and interfacial properties of conventional cationic surfactants and the ionic liquid surfactant 1-tetradecyl-3- methylimidazolium bromide ([C14mim]Br)

Article abstract of DOI:10.1007/s11743-012-1431-3

The surface properties and mixed micellization behavior of binary combinations of an ionic liquid surfactant, namely, 1-tetradecyl-3- methylimidazolium bromide ([C₁₄mim]Br) with common cationic surfactants viz. tetradecyltrimethylammonium bromide and tetradecylpyridinium bromide in the presence of sodium bromide (NaBr) were investigated by surface tension and conductivity measurements. The critical micelle concentration (CMC) and interfacial parameters, such as the maximum surface excess (Γ_max), minimum area per molecule (A_min) and surface pressure at the CMC (π_CMC) were determined from the surface tension data. The CMC and Γ_max values were found to decrease with increasing salt concentrations. The Δ_Gad° and Δ G_m° values are negative indicating the spontaneity of micelle formation.

Full text of DOI:10.1007/s11743-012-1431-3

J Surfact Deterg (2013) 16:531–538
DOI 10.1007/s11743-012-1431-3
ORIGINAL ARTICLE
Salt Effect on Mixed Micelle and Interfacial Properties
of Conventional Cationic Surfactants and the Ionic Liquid
Surfactant 1-Tetradecyl-3-methylimidazolium
Bromide ([C mim]Br)
1
4
Genxiang Luo
Chunsheng Liu
•
Xinjie Qi
•
•
Chunyu Han
•
Jianzhou Gui
Received: 3 June 2012 / Accepted: 10 December 2012 / Published online: 25 December 2012
Ó AOCS 2012
Abstract The surface properties and mixed micellization
behavior of binary combinations of an ionic liquid sur-
factant, namely, 1-tetradecyl-3-methylimidazolium bro-
mide ([C mim]Br) with common cationic surfactants viz.
applications. Especially, ILs composed of 1-alkyl-3-methyl
?
imidazolium cation [C mim] have been extensively
n
studied in the field of colloid and interface science in recent
years [3–5]. A literature survey reveals that the various
physicochemical properties of micellar aggregates are very
sensitive to environmental conditions such as temperature,
additives, etc. Jalali et al. [6] have measured CMC of
cetyltrimethylammonium bromide (CTAB) at various
temperatures and in the presence of potassium bromide.
The results indicated that the critical micelle concentration
(CMC) value of CTAB increased with increasing temper-
ature, but decreased drastically with the addition of inor-
ganic salts to water. Rather than changing the temperature,
the usual way to modify the physicochemical properties of
a given surfactant solution is to use external additives, such
as cosolvents, cosurfactants, electrolytes, polar organics,
nonpolar organics, etc. [7–9]. The effect of an additive can
significantly influence the CMC, surface tension value at
CMC and adsorption densities at the air–liquid interface
1
4
tetradecyltrimethylammonium bromide and tetradecylpy-
ridinium bromide in the presence of sodium bromide
(
NaBr) were investigated by surface tension and conduc-
tivity measurements. The critical micelle concentration
CMC) and interfacial parameters, such as the maximum
surface excess (Cmax), minimum area per molecule (Amin
(
)
and surface pressure at the CMC (pCMC) were determined
from the surface tension data. The CMC and Cmax values
were found to decrease with increasing salt concentrations.
ꢀ
ꢀ
The DG and DGm values are negative indicating the
spontaneity of micelle formation.
ad
Keywords Salt effects ꢁ Mixed micellization ꢁ
Ionic liquid surfactants ꢁ Cationic surfactants ꢁ
Interfacial properties
[
10–14]. It is now well established that the micelle for-
mation tendency and the micellar structural features of
classical cationic surfactants based on alkyl trimethyl
ammonium or alkyl pyridinium head groups in aqueous
media are drastically affected by inorganic salts, organic
counter-ions and even non-electrolytes such as urea etc.
[15–19]. Aguiar et al. [20] studied the thermodynamics and
micellar properties of tetradecyl trimethyl ammonium
bromide in formamide–water mixtures. Jalali et al. [21]
studied the thermodynamics of micellization of hexadecyl
pyridinium bromide in mixed solvents containing dilute
electrolyte solutions. Therefore the additives of salts or
non-electrolytes are expected not only to influence the
aggregation behavior of traditional surfactants but also
modify interfacial properties of ionic liquids. And the
appearance of the surface-active ionic liquids has brought
Introduction
Ionic liquids (ILs) have gained great attention for their
promising role as alternative media in catalysis, separation,
and electrochemical processes due to their unique chemical
and physical properties [1, 2]. Knowledge of the aggrega-
tion behavior of ILs is a vital part for understanding how
these compounds participate as components in the practical
G. Luo (&) ꢁ X. Qi ꢁ C. Han ꢁ C. Liu ꢁ J. Gui
Department of Chemistry, School of Chemistry
and Materials Science, Liaoning Shihua University,
Fushun 113001, People’s Republic of China
e-mail: genxiangluo@yahoo.com.cn
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J Surfact Deterg (2013) 16:531–538
new insights into the research on mixed systems containing
ionic liquid-type surfactants and additives. Dong et al. [22]
studied the effect of sodium halides on the CMCs of
above were very pure and were used without any further
purification. TPB and 1-Bromotetradecane were bought
from the Beijing Hengye Zhongyuan Chemical Co., Ltd.,
and Beijing Jinlong Chemical Reagent Co., Ltd., respec-
tively, and used as received. NaBr was obtained from
Tianjin Standard Science And Technology Co., Ltd. Ethyl
acetate was an analytical grade reagent. Triply distilled
water from an SYZ-A Quartz sub-boiling distillation
apparatus was used for the preparation of solutions. The
experiments were performed at 298 K.
[
C mim]Br, [C mim]Br, and [C mim][BF ] in water,
10 12 12 4
and it was reported that the CMCs of ionic liquid surfac-
tants are reduced by all the sodium halides. In the present
era, the rising demand for newer materials with improved
and novel properties has given emphasis to the studies of
surfactant additives systems [23].
In addition, mixed micelles are considered to be more
versatile than a single surfactant [24–26] and have many
applications in surface activity, detergency, wetting,
spreading and foaming. Some researches into mixed
micelle formation have focused on pure water only. Tejas
et al. [27] studied the micellization process of binary sur-
factant mixtures containing cationic surfactants and non-
ionic surfactant in water. The results showed synergistic
interaction between binary surfactant mixtures containing
different cationic and nonionic surfactants in water at dif-
ferent mole fractions. The critical micelle concentrations of
mixed binary cationic surfactant systems have been deter-
mined in water by conductivity measurements by Treiner
et al. [28]. Thomaier et al. [29] have studied a colloidal
system, which is based on a mixture of two ionic liquids.
The observations provide strong evidence that a mixture of
two ionic liquids can form a colloidal system as much as a
common surfactant does in water. Rosen et al. [30] studied
the electrolyte effect on the interaction of cationic and
anionic surfactants in a mixed monolayer. They found that
the interaction between these surfactants is weaker with the
addition of an electrolyte. Thus, it would be of interest
and importance, from both the practical and academic
viewpoints, to investigate systems containing multiple
surfactants. Hence, in the present study, we investigated the
mixed micelle and adsorption properties of binary surfac-
tant systems containing the ionic liquid surfactant
Synthesis of the Ionic Liquid [31, 32]
[C mim]Br was synthesized by solvent-free alkylation of
1
4
1-methyl imidazole (0.1 mol) with 1-tetradecyl bromide
(0.1 mol). The mixture was stirred in a three-necked flask
with a reflux condenser for 12 h at 343–353 K under a dry
N atmosphere and then cooled to room temperature. At the
2
beginning of the reaction, 1-tetradecyl bromide were added
dropwise to the flask with a constant pressure dropping
funnel. The resulting products were recrystallized three
times from ethyl acetate to remove any unreacted reagents.
The ionic liquid was thereafter dried for 8 h in a vacuum
under reduced pressure at 333 K to yield a white solid. The
1
compound was analyzed by H-NMR, and FT-IR spec-
troscopy. The spectral data are consistent with the structure
expected.
Methods
Surface Tension Measurements
Surface tensions of aqueous solutions of single and mixed
surfactants at various concentrations were carried out on a
Surface Tensiometer (JK99B, Shanghai Zhongchen Digital
-1
[
C mim]Br and cationic surfactants viz. tetradecyl trimethyl
14
Technology Co., Ltd., accuracy ± 0.05 mN m ). Temper-
ature was controlled using an DK-S22 thermostatic bath
(accuracy ± 0.1 °C). The surface tension was determined
by the plate method. The platinum plate was thoroughly
cleaned and dried with the flame before each measurement.
The measurements of the surface tension of pure water at
298 K were performed to calibrate the tensiometer and to
check the cleanliness of the glassware. All measurements
were repeated at least three times. The values of the CMC
and the surface tension at the CMC (cCMC) were deter-
mined from the turning point in surface tension curves
(c-log C curves).
ammonium bromide (TTAB) and tetradecyl pyridinium
bromide (TPB) in the absence and presence of NaBr in pure
and mixed systems. For this purpose, the results have been
discussed from the influence of the concentration of salt on
the CMC, the counterion binding (g), the surface excess
(Cmax) and minimum area per molecule (Amim) in aqueous
solutions. The thermodynamic parameters of micellization
and adsorption were also computed and discussed.
Experimental Section
Materials
Electrical Conductivity Measurements
TTAB and 1-Methyl imidazole were purchased from a
Johnson Manhey Company, Lancs. These two products
The conductance measurements were taken with a DDS-
307 conductivity meter (Shanghai Precision Scientific
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J Surfact Deterg (2013) 16:531–538
533
Instrument Co., Ltd.) using a conductivity cell with a
-
constant 1.0 cm . The cell was calibrated with the aque-
1
-
3
ous 0.01 mol dm KCl solutions. Accuracy of the mea-
sured conductance was within ± 1 %. The surfactant
conductance was measured after thorough mixing and
temperature equilibration. At least three measurements
were made every time and the mean values were taken to
calculate the specific conductivities. The measurement
details can be found elsewhere [33–36]. The electrical
conductivity measurement is suitable for obtaining the
CMC and the degree of counterion association (g) for ionic
micelle aggregates. The location of the break point
appearing in the plot of specific conductivity versus con-
centration gives the CMC, whereas the ratio between the
slopes of the plot above and below the CMC can give the
Fig. 1 Equilibrium surface tension of [C14mim]Br at different salt
concentrations versus logarithm of the total concentration
counterion dissociation constant (k ) [37]. From which,
0
g can be calculated as g = 1 - k0.
Obviously, for all the binary systems, the CMC values
determined by either method are relatively close to each
other and the results for single surfactants have corrobo-
rated the literature values. From Table 1 it can be inferred
that the CMC values of the pure and mixed systems
decrease with an increased concentration of salt, which
indicates the significant role of electrolytes for the micel-
lization process. The decrease in the CMC values may be
interpreted as follows. The cationic surfactants form an
ionic monolayer at the air–water interface, the addition of
electrolyte anions leads to the reduction in the thickness and
potential ofthe electricdoublelayer atthe interfacebecause of
the electrostatic interaction between opposite charges [42].
Consequently, it induces the screening of the electrostatic
repulsion among the polar head groups and leads to a
remarkably lower CMC in comparison with the salt free
system. The repulsion between head groups of surfactants is
one of the main factors opposing micellization [43].
Results and Discussion
Effect of Sodium Salt on Critical Micelle Concentration
(
CMC)
Surface tension and conductivity of single and mixed
systems at different salt concentrations were measured to
obtain the CMC. Figure 1 shows the plot of equilibrium
surface tension (c) versus the logarithm of the solution
concentration for [C mim]Br in the presence of sodium
1
4
bromide at different concentrations and the CMC values of
C mim]Br determined from this plot are given in
[
14
Table 1. The presence of the electrolyte has a great effect
on micelle formation. The surface tension as well as the
CMC of C mimBr is reduced along with the increase in
1
4
the concentration of NaBr solution. An analogous trend has
also been observed for cetyl pyridinium chloride (CPyCl)
in the presence of NaCl and NaBr [18].
As representative examples, Figs. 2 and 3 show plots of
the equilibrium surface tension (c) versus logC and the
specific conductivity (j) against total surfactant concen-
tration, respectively, for 1:1 [C mim]Br ? TPB mixtures
Effect of Sodium Salt on Counterion Binding
Ionic micelles bind a considerable amount of counterions,
which can be estimated by calculating the degree of
counterion binding (g) at the micellar surface [33, 36, 44].
The results are presented in Table 1, and the values allow
us to evaluate the effect of salt concentration on the degree
of counterion binding on the aggregates surface of the
systems. A large increase in g values can be seen, indi-
cating better packed aggregates of surfactants in salt
aqueous solutions. When the concentration of the salt is
low, the g values increase with increasing of salt concen-
trations for a given salt, which is related to the increase in
charge density of the stern layer of the micelles formed,
thereby increasing the number of bromide ions bound to
micelles [45].
1
4
in solutions with different salt concentrations. It can be
seen in Fig. 3 that the slopes of the linear region above the
CMC are smaller than those below the CMC. This is a
consequence of counterion binding at the surface of the
micellar aggregates. In other words, there is an effective
loss of ionic charges since a number of counterions are
confined to the micellar surface. Similar behavior was
obtained for other surfactant systems. From these plots, the
counterion association (g) properties of all the systems
were determined. The CMC values of these mixed systems
in absence and presence of NaBr are also summarized in
Table 1.
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J Surfact Deterg (2013) 16:531–538
Table 1 CMC (mM) and g values of pure and mixed surfactants in
absence and presence of sodium salt at 298 K by different methods
Effect of Sodium Salt on Interfacial Properties
The values of surface excess, for the studied surfactants at
air/solution interface near its CMC in the presence of the
electrolyte were calculated from the respective surface
tension data using the Gibbs adsorption equation [46]:
Salt concentration CMC/mM
(M)
g
Tensiometry Conductometry Average
CMC
[C14mim]Br
"
#
ꢀ
ꢁ
0.000
2.76 (2.80)
38]
2.53 (2.60)
[38]
2.65
0.747
1
1
oc
o log C
Cmax ¼ ꢂ 2
ð1Þ
[
c0
:303RT 1 þ
c0þce
T
0
0
0
0
0
0
0
.0005
.001
.005
.010
.020
.050
.100
2.33
2.27
1.40
1.05
0.75
0.29
0.20
2.50
2.30
1.63
0.93
0.91
0.28
0.24
2.42
2.29
1.52
0.99
0.83
0.29
0.22
0.762
0.802
0.823
0.830
0.863
0.804
0.601
where c is the interfacial tension, (qc/qlogC)max, T is the
maximum slope in c versus logC plot; R is the universal
gas constant; T is the absolute temperature; c and c is the
e
0
electrolyte concentration and CMC, respectively. In the
absence of electrolyte, Eq. (1) becomes:
ꢀ
ꢁ
1
oc
o log C
TTAB
Cmax ¼ ꢂ 2
ð2Þ
:303nRT
0.0000
3.43 (3.80)
3.07 (3.40)
[40]
3.25
0.764
T
[39]
where n is a constant, which depends on the number of
species constituting the surfactant. With a 1:1 ionic sur-
factant, in the absence of extra electrolyte, the thermody-
namic treatment requires n = 2, implying an equimolar
ratio of surfactant anion and counter cation in the interface
0
0
0
0
0
0
0
.0005
.0010
.0050
.0100
.0200
.0500
.1000
3.01
2.79
2.29
1.54
1.05
0.66
0.45
3.08
2.86
2.35
1.27
0.91
0.63
0.37
3.05
2.83
2.32
1.41
0.98
0.65
0.41
0.473
0.524
0.674
0.692
0.700
0.834
0.906
[
36]. For the surfactant mixtures, n = n a ? n a , where
1
1
2 2
n and n are the number of species of surfactant 1 and 2,
1
2
respectively; a and a are the molar fractions (on a sur-
1
2
TPB
factant-only basis) of surfactants 1 and 2, respectively, in
the bulk phase [47, 48]. The value of n is 2 in all binary
systems in the absence of electrolyte in this work.
0
.0000
2.57 (3.11)
2.80 (3.11)
[41]
2.69
0.689
[41]
0
0
0
0
0
0
0
.0005
.0010
.0050
.0100
.0200
.0500
.1000
2.47
2.26
1.47
1.03
0.73
0.38
0.20
2.44
2.13
1.13
0.86
0.59
0.33
0.16
2.46
2.20
1.30
0.95
0.66
0.36
0.18
0.709
0.714
0.729
0.732
0.740
0.715
0.705
The surface excess is a measure of effectiveness of the
surfactant adsorption, the increase in which has a sub-
stantial effect in applications e.g., floatation, improved
oil recovery, in-situ and ex-situ soil remediation, deter-
gency, setting, surfactant based separation processes,
since coherently packed interfacial films have different
properties from that of non-coherent loosely packed films
[C14mim]Br ?TTAB(1:1)
0
.0000
.0005
.0010
.005
2.67
3.00
2.76
1.68
1.08
0.63
0.36
0.22
2.61
2.85
2.72
1.70
1.02
0.64
0.34
0.21
2.64
2.93
2.74
1.69
1.05
0.64
0.35
0.22
0.594
0.722
0.727
0.728
0.759
0.859
0.812
0.742
[
49].
The Cmax was used to calculate the minimum area per
surfactant molecule (Amin) at the air/solvent interface using
0
0
0
0
0
0
0
the relationship:
.0100
.0200
.0500
.1000
1
018
Amin
¼
ð3Þ
NACmax
18
where the 10 factor arises out of conversion from m to
[C14mim]Br ? TPB(1:1)
nm and N is the Avogadro’s number. C
and Amin are
max
A
0
.0000
.0005
.0010
.0050
.0100
.0200
.0500
.1000
2.59
2.42
2.21
1.53
0.91
0.49
0.31
0.17
2.54
2.42
2.21
1.47
0.80
0.55
0.29
0.15
2.57
2.42
2.21
1.50
0.86
0.52
0.30
0.16
0.680
0.620
0.695
0.700
0.718
0.856
0.881
0.683
-2
2
-1
expressed in mol m and nm mol units, respectively.
The values of the surface pressure at the CMC (pCMC) were
obtained from Eq. (4):
0
0
0
0
0
0
0
pCMC ¼ c ꢂ c
where c being the surface tension of the pure solvent and
cCMC being the surface tension at the CMC. This parameter
(
ð4Þ
0
CMC
0
pCMC) indicates the maximum reduction in surface tension
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J Surfact Deterg (2013) 16:531–538
535
addition of electrolyte, the noticeably prominent and
interesting features of the maximum surface excess are
that the values are always higher in salt solutions as
compared in pure water. The Amin values of these systems
nearly followed a reverse order. A similar trend has been
observed for ionic surfactants [53]. Added electrolyte
enhances the adsorption of surfactants at the air–water
interface thereby decreasing the surface area coverage per
molecule of surfactants. The enhancement of adsorption
by the addition of electrolyte can be explained as being
due to their salting out effect. In addition, the magnitude
of Amin is low, suggesting that the air/water interface is
closely packed and therefore that the surfactant molecules
at the interface are oriented perpendicularly to the
interface.
Fig. 2 Equilibrium surface tension of mixed 1:1 [C14mim]Br/TPB
at different salt concentrations versus logarithm of the total
concentration
Thermodynamic Parameters of Aggregation
The standard free energy of micellization per mole of
ꢀ
monomer unit (DG ) for pure surfactants and their mix-
tures [54, 55] can be obtained as,
m
ꢀ
DG ¼ ð1 þ gÞRT ln XCMC
in which the new term XCMC is the CMC of a surfactant
ð5Þ
m
expressed in mole fraction units. Using the (CMC)av and
ꢀ
the g values presented in Table 1, the DGm values for the
studied pure and mixed surfactants systems have been
ꢀ
computed and listed in Table 2. The DGm values reveal
that all the systems have considerable spontaneity in the
process of micelle formation. The standard free energy of
ꢀ
interfacial adsorption DG ) at the air/water interface is
obtained from the relation,
ad
ꢂ
ꢃ
ꢀ
ꢀ
p
CMC=
DG ¼ DG ꢂ
ð6Þ
ad
m
Cmax
where pCMC is the surface pressure at CMC, and Cmax is the
maximum surface excess of the amphiphile.
Fig. 3 Specific conductivity of mixed 1:1 [C14mim]Br ? TPB at
different salt concentrations versus total surfactant concentration
ꢀ
ꢀ
In Table 2, it can be observed that the DGm and DG
ad
values are negative in both the absence and presence of
salt, indicating a spontaneous micellization process due to
hydrophobicity of amphiphiles, which leads them toward
air–water interface. The free energy of aggregation is
always more negative in presence of salt as compared in
pure water indicating easy facilitation of the aggregation
caused by the dissolution of surfactant molecules and,
hence, becomes a measure of the effectiveness of the sur-
factant to lower the surface tension of the solvent.
The results of Cmax, Amin and pCMC for the pure and
mixed surfactants in aqueous solutions in the absence and
presence of salt at 298.15 K are presented in Table 2. It is
clear that the pCMC values increase with increasing con-
centration of NaBr, and eventually, cCMC decreases. It is
well known that inorganic salt affects the adsorption of
ionic surfactants at the air–water interface and the aggre-
gation of them in aqueous solution since the salt screens the
charge of ionic head groups and results in the reduction of
the electrostatic repulsion between the head groups within
the adsorption film and the micelle [50–52]. With the
ꢀ
process by the addition of salt. Besides, the values of DG
ad
ꢀ
is greater than that of DGm for all the systems. This vari-
ation is a measure of the spontaneity difference of the two
processes. The adsorption process is rather stronger than
the bulk process of micellization. Thus, the head group
architecture of the surfactants plays a decisive role in the
surface chemical behaviors of the surfactants. From this, it
may be concluded that micelle formation is spontaneous
compared to adsorption.
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J Surfact Deterg (2013) 16:531–538
Table 2 Surface pressure at the
CMC (pCMC), the maximum
surface excess (Cmax), the
minimum surface area per
molecule (Amin), Gibbs free
6
ꢀ
ꢀ
ad
Salt concentration
M)
c
CMC
(m Nm
p
CMC
(m Nm
10 Cmax
(mol m
A
min
2
(nm mol
DG
DG
m
-1
)
-1)
-2
-1
)
(
)
(kJ/mol) (kJ/mol)
C14mimBr
ꢀ
0.000
35.06
34.90
34.39
34.07
33.74
33.28
32.43
31.94
35.28
35.45
35.96
36.28
36.61
37.07
37.92
38.41
2.06 (1.96) [38] 0.81 (0.85) [38] -25.69
-42.82
-43.27
-44.61
-45.44
-48.41
-49.69
-48.06
-46.22
energy of micellization (DG ),
and the standard Gibbs energy
m
0.0005
0.001
2.09
2.06
2.25
2.15
2.19
3.26
3.00
0.80
0.81
0.74
0.77
0.76
0.51
0.55
-26.31
-27.15
-29.32
-31.38
-32.76
-36.43
-33.42
ꢀ
of adsorption (DG ), values of
surfactants in the presence and
absence of salt at 298 K
ad
0.005
0.010
0.020
0.050
0.100
TTAB
0.000
0.0005
0.001
0.005
0.010
0.020
0.050
0.100
32.78
31.92
31.85
31.40
30.72
30.51
31.09
31.00
37.57
38.43
38.50
38.95
39.63
39.84
39.26
39.35
2.09 (2.7) [38]
2.27
0.79 (0.62) [38] -25.05
-53.73
-38.09
-37.27
-38.51
-39.19
-39.93
-45.59
-50.56
0.73
0.65
0.57
0.49
0.45
0.52
0.58
-21.15
-22.17
-25.17
-27.53
-29.19
-33.36
-36.85
2.55
2.92
3.40
3.71
3.21
2.87
TPB
0
0
0
0
0
0
0
0
.000
35.19
34.32
34.30
34.18
33.96
33.77
32.59
32.47
35.16
36.03
36.05
36.17
36.39
36.58
37.76
37.88
2.02 (2.99) [41] 0.82 (0.55) [41] -24.78
-42.19
-40.85
-43.09
-45.95
-43.93
-44.99
-48.94
-50.95
.0005
.001
.005
.010
.020
.050
.100
2.34
2.11
2.07
2.59
2.73
2.48
2.61
0.71
0.79
0.80
0.64
0.61
0.67
0.64
-25.45
-26.00
-28.48
-29.88
-31.59
-33.71
-36.44
C14mimBr ? TTAB
0.000
0.0005
0.001
0.005
0.010
0.020
0.050
0.100
34.27
32.69
32.52
32.44
32.23
32.21
32.00
31.84
34.36
35.95
36.11
36.20
36.41
36.43
36.64
36.80
2.15
2.54
2.19
3.18
2.96
3.05
3.09
3.11
0.77
0.65
0.76
0.52
0.56
0.54
0.54
0.53
-23.46
-24.90
-25.26
-27.34
-29.91
-33.89
-35.74
-36.37
-39.44
-39.05
-41.75
-38.72
-42.21
-45.83
-47.60
-48.20
C14mimBr ? TPB
0.000
0.0005
0.001
0.005
0.010
0.020
0.050
0.100
33.76
33.73
33.31
33.69
33.12
32.88
32.52
32.03
36.46
36.49
36.91
36.53
37.10
37.34
37.70
38.19
2.39
2.46
2.69
2.52
2.78
2.67
2.83
2.98
0.69
0.68
0.62
0.66
0.60
0.62
0.59
0.56
-24.84
-24.19
-25.69
-27.40
-30.06
-34.79
-37.82
-36.46
-40.10
-39.02
-39.41
-41.90
-43.41
-48.78
-51.14
-49.28
1
23

J Surfact Deterg (2013) 16:531–538
537
Conclusions
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an imidazolium ionic liquid were studied in an inorganic
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1
ꢀ
ꢀ
DG and DG values were both negative and the
m
ad
adsorption process is stronger than the bulk process of
micellization. The addition of NaBr was found to exert a
remarkable influence on the aggregation behavior of single
surfactants [C mim]Br, TTAB, TPB and their binary
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1
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all the systems decreased drastically in the presence of salt
indicating that the anions from the salt preferentially
adsorb onto the surface of the charged aggregate and
facilitate the aggregate growth by suppressing the main
impediment of electrostatic repulsion among head groups.
Additionally, the values of Cmax are always higher in salt
solutions as compared to in pure water due to their salting
out effect. Therefore, the aggregation behavior of single
and binary surfactant systems containing the ionic liquid
surfactant in aqueous solutions can be regulated by the
addition of salts with different concentrations for a par-
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Acknowledgments The work was financially supported by the
Program for New Century Excellent Talents in University (NCET-11-
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Author Biographies
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9. Mateos IG, Velazquez MM, Rodriguez L (1990) Critical micelle
concentration determination in binary mixtures of ionic surfac-
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Genxiang Luo is a professor at Liaoning Shihua University. His
primary research field is colloids and surfactants. His current research
involves the synthesis and surface properties of ionic liquid
surfactants.
4
4
0. Barry BW, Morrison JC, Russell GFJ (1970) Prediction of the
critical micelle concentration of mixtures of alkyltrimethylam-
monium salts. J Colloid Interface Sci 33:554–561
Xinjie Qi is a postgraduate student of physical chemistry at Liaoning
Shihua University. Her current research involves the synthesis and
surface properties of ionic liquid surfactants.
1. Basu Ray G, Chakraborty I, Ghosh S, Moulik SP (2007) Studies
on binary and ternary amphiphile combinations of tetra-
decyltrimethylammonium bromide (C14TAB), tetradecyl tri-
phenylphosphonium bromide (C14TPB), and tetradecyl
pyridinium bromide (C14PB). A critical analysis of their inter-
facial and bulk behaviors. J Phys Chem B 111:9828–9837
2. Para G, Jarek E, Warszynski P (2006) The Hofmeister series effect
in adsorption of cationic surfactants—theoretical description and
experimental results. Adv Colloid Interface Sci 122:39–55
3. Shamsipur M, Alizadeh N, Gharibi H (1997) Physicochemical
studies of the hexadecylpyridinium bromide micellar system in
the presence of various concentrations of sodium bromide using a
surfactant-selective electrode. Indian J Chem 36A:1031–1037
4. Das C, Chakraborty T, Ghosh S, Das B (2008) Mixed micelli-
zation of anionic–nonionic surfactants in aqueous media: a
physicochemical study with theoretical consideration. Colloid
Polym Sci 286:1143–1155
Chunyu Han studied analytical chemistry at Liaoning Shihua
University where he received his master’s degree in 2008. He then
joined the group of Prof. Genxiang Luo. He is currently working as an
associate professor in the chemistry department at Liaoning Shihua
University. His research involves the synthesis and characterization of
surfactants.
4
4
Chunsheng Liu is an associate professor at the Liaoning Shihua
University. His areas of interest are the synthesis and application of
surfactants.
4
4
Jianzhou Gui is an associate professor at Liaoning Shihua Univer-
sity. His primary research field is green chemistry. His current
primary research involves the synthesis of functionalized ionic
liquids.
5. Chauhan MS, Sharma K, Kumar G, Chauhan S (2003) A con-
ductometric study of dimethylsulfoxide effect on micellization of
1
23