Effect of bolaform counterions on the adsorption of sodium dodecyl sulfonate at the air/water interface

Article abstract of DOI:10.1007/s11743-013-1486-9

The effect of quaternary ammonium-based bolaform counterions (Bolan-series where n is the number of carbon atoms between the heads) on the adsorption of sodium dodecyl sulfonate (SDDS) at the air/water interface has been studied using surface tension measurements. The results showed that the Bolan counterions strongly interacted with SDDS even at very low concentrations. This reduced the CMC and C₂₀ in the presence of Bolan counterions. The SDDS packed more tightly at the interface under the inducement of Bolan counterions and thus the occupied area per surfactant molecule decreased. Another bolaform counterion series (Bolanph) with a benzene ring attached on each side of the quaternary ammonium heads could further enhance the interaction with SDDS. This is due to the fact that the attached aromatic rings penetrate into the gaps between the surfactant headgroups, which provide an additional association force besides the electrostatic attractions. The present results suggested an approach to construct gemini-like surfactants depending on the electrostatic attraction between the bolaform counterions and the conventional ionic surfactants or an additional hydrophobic force made by the attached aromatic rings.

Full text of DOI:10.1007/s11743-013-1486-9

J Surfact Deterg
DOI 10.1007/s11743-013-1486-9
ORIGINAL ARTICLE
Effect of Bolaform Counterions on the Adsorption of Sodium
Dodecyl Sulfonate at the Air/Water Interface
•
Jianxi Zhao Duoping Yang Yi You
•
Received: 12 July 2012 / Accepted: 10 April 2013
Ó AOCS 2013
Abstract The effect of quaternary ammonium-based
bolaform counterions (Bolan-series where n is the number
of carbon atoms between the heads) on the adsorption of
sodium dodecyl sulfonate (SDDS) at the air/water interface
has been studied using surface tension measurements. The
results showed that the Bolan counterions strongly inter-
acted with SDDS even at very low concentrations. This
reduced the CMC and C20 in the presence of Bolan coun-
terions. The SDDS packed more tightly at the interface
under the inducement of Bolan counterions and thus the
occupied area per surfactant molecule decreased. Another
bolaform counterion series (Bolanph) with a benzene ring
attached on each side of the quaternary ammonium heads
could further enhance the interaction with SDDS. This is
due to the fact that the attached aromatic rings penetrate
into the gaps between the surfactant headgroups, which
provide an additional association force besides the elec-
trostatic attractions. The present results suggested an
approach to construct gemini-like surfactants depending on
the electrostatic attraction between the bolaform counteri-
ons and the conventional ionic surfactants or an additional
hydrophobic force made by the attached aromatic rings.
Introduction
For the counterions, the bolaform molecular structure is
rather unique which forms separately, charge controlled by
a spacer as seen in Scheme 1. Early studies showed that the
spacer length strongly influenced the interaction of the
counterions with the oppositely charged ionic surfactants
and thus their adsorption and aggregation [1–8]. For
instance, Moroi et al. studied the effects of a series of
cationic bolaform counterions, 1,10-(1,x-alkanediyl)bis-
pyridinium, on the micellization and the solubility of
alkane-1-sulfonates in aqueous solution. They found that
the charge separation of up to six methylene groups did not
make much difference in the critical micelle concentration
(CMC) but of from 8 to 14 methylene groups considerably
reduced the CMC [1, 5]. The micelle aggregation number
monotonously decreased with increasing the methylene
groups in the spacer and passed through a minimum around
8 CH2 groups [3]. And the surface excess also monoto-
nously decreased with increasing the methylene groups and
produced a minimum around 8 CH2 groups [3].
Recently, bolaform counterions have attracted much
attention because they have perhaps the potential to con-
struct gemini surfactants. A gemini surfactant has a dimeric
molecular structure, i.e., it is made up of two monomer
surfactants linked at the headgroups by a spacer [9].
Gemini surfactants have been extensively studied and are
known to exhibit a very high surface activity. Up to now,
the preparation of gemini surfactants still depends on
chemical synthesis, in which the linking between the
headgroup and the spacer in provided by a covalent bond.
The chemical synthesis is always a troubling and time
consuming process. Thus, another possible approach
attracts our interest, i.e. testing the use of a bolaform
counterion associating two conventional ionic surfactant
Keywords Bolaform counterions ꢀ Electrostatic
attractions ꢀ Gemini-type surfactants
J. Zhao (&) ꢀ D. Yang ꢀ Y. You
Institute of Colloid and Interface Chemistry, College of
Chemistry and Chemical Engineering, Fuzhou University,
Fuzhou, Fujian 350108, China
e-mail: jxzhao.colloid@fzu.edu.cn
D. Yang
e-mail: n080420075@fzu.edu.cn
Y. You
e-mail: youyi@fzu.edu.cn
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J Surfact Deterg
Compounds
Abbreviation
SDDS
Sodium dodecyl sulfonate
SO3Na
5
Scheme 1 Schematic representation of bolaform counterion
Ethanediyl-α,ω-bis(ethyldimethylammonium bromide)
Bola2Et
N
2Br
N
molecules through electrostatic attraction. Under the elec-
trostatic force, a ‘‘pseudo molecule’’ with a gemini-type
structure is expected to form. This approach is undoubtedly
very convenient for ‘‘preparing’’ a gemini surfactant. Very
recently, we observed that bolaform counterions in the
aqueous subphase can indeed effectively control the
monolayer behavior of sodium hexadecyl sulfate [10]. This
seems to indicate the feasibility of this new approach. At
present, however, the related knowledge is lacking and
there is a great need for experimental results. For this
purpose, we continue to report the effect of bolaform
counterions on the adsorption behavior of sodium dodecyl
sulfonate (SDDS) at the air/water interface in this paper.
Alkanediyl-α,ω-bis(trimethylammonium bromide)
Bolan (n=4, 6, 12)
N
N
2Br
n
Tetramethylammonium Bromide
TMAB
N
Br
Alkanediyl-α,ω-bis(benzyldimethylammonium bromide) Bolanph (n=2, 4, 6)
N
N
2Br
n
Benzyltrimethylammonium Bromide
BTMAB
Br
N
1,6-Hexanediaminium-N1,N6-bis[6-[dimethyl(phenylmethyl)ammonio]hexyl]-
N6 -tetramethyl tetrabromide Tetra6
1
N
Experimental
,
Materials
N
N
N
N
4Br
6
6
6
All compounds used in the present work, including their
chemical structure and abbreviation, are listed in
Scheme 2.
Scheme 2 Chemical structure, name and abbreviation
TMAB and BTMAB were purchased from Acros and
used as received. SDDS was the product from TCI (Tokyo
Chemical Industry Co., Ltd.) and was used after re-crys-
tallization three time from ethanol. The others were syn-
thesized in our laboratory, which we described in a previous
paper [10] except Tetra6. All the solutions were prepared
with Milli-Q water (resistivity = 18.2 MX cm-1).
was heated to 50 °C, after which N,N-dimethyl-1-phe-
nylmethanamine (1.35 g, 10 mmol) was dissolved in
10 mL acetone and added to the three-necked flask drop-
wise. The reaction lasted 24 h and the solid product was
obtained by filtration. The crude product was washed with
acetone. Yield: 1.8 g (47 %).
Synthesis of Tetra6
N,N,N0,N0-tetramethylhexane-1,6-diamine (2)
The synthesis route of Tetra6 is represented in Scheme 3
and the procedure is described as follows:
1,6-Dibromohexane (12.1 g, 50 mmol) was dissolved in
100 mL ethanol, and then dimethylamine aqueous solution
(33 %wt, 23.9 g, 250 mmol) and K2CO3 (6.9 g, 50 mmol)
were added. After the reaction was complete at ambient
temperature within 24 h, the mixture was acidified to
pH = 1*2 using HCl. The mixture was extracted by
petroleum ether twice, and the aqueous layer was reserved.
A NaOH aqueous solution was added to the aqueous layer
until pH = 12 * 13. This basic mixture was extracted by
ether three times. The organic layer was combined and the
ether was removed by rotary evaporation. The product (2)
was collected by atmospheric distillation at 206 °C. Yield:
4.3 g (40 %).
The materials for the synthesis: 1,6-dibromohexane,
were purchased from TCI (Tokyo Chemical Industry Co.,
Ltd.) and the others were from SCR (Sinopharm Chemical
Reagent Co., Ltd.) and used without further treatment. All
the materials were of analytical grade.
N-benzyl-6-bromo-N,N-dimethylhexan-1-aminium
bromide (1)
1,6-Dibromohexane (7.32 g, 30 mmol) and 10 mL acetone
was put into a 100-mL three-necked flask and the mixture
123

J Surfact Deterg
Scheme 3 Synthesis route of
Tetra6
N
N
N
N
4Br
(3)
N
Br
N
Br
(1)
(2)
Br
(3)
Br
N
N
HN
2
1,6-Hexanediaminium-N1,N6-bis[6-
(SDDS) in the bulk solution. Different from our previous
study where 500 mmol L-1 counterions were contained in
the subphase, only a small quantity of the bolaform
counterions exits in the present system, i.e. always keeping
a constant ratio of 2:1 for SDDS to bolaform counterion.
From Fig. 1, one can obtain the critical micelle concen-
tration (CMC) by the break point, the minimum surface
tension (cCMC) at the CMC and the concentration (C20)
required to reducing 20 mN m-1 surface tension of water.
Generally, the three parameters are used to characterize the
ability to form micelles, the effectiveness and the effi-
ciency in surface tension reduction, respectively [11]. The
data are listed in Table 1.
[dimethyl(phenylmethyl)ammonio]hexyl]-N1,N6-
tetramethyl tetrabromide (3)
The compound (1) (9.47 g, 0.025 mol), (2) (1.72 g,
0.01 mol) and ethanol (30 mL) were put together in a
250-mL flask equipped with an Allihn condenser. The
temperature was raised so as to dissolve the reactant, fol-
lowing which 40 mL acetone was poured into the flask.
The reaction lasted 48 h and a precipitate was obtained.
The crude precipitate product was washed with acetone and
recrystallized three times from ethanol/acetone. Yield:
2.5 g (27 %).
1H NMR (D2O, 400 MHz): d 1.35 (12H, m, CH2), d 1.83
(12H, m, CH2), d 2.98 (24H, s, N-CH3), d 3.25(12H, m,
N-CH2), d 4.44(4H, s, Ar-CH2), d 7.53(10H, m, Ar–H).
Anal. Calc. for: C40H74 N4Br4ꢀH2O: C, 50.64; H, 8.07; N,
5.91; Found: C, 50.40; H, 8.03; N, 5.83.
For the Bolan-series, the characteristic parameters listed
in Table 1 clearly show that the Bolan counterions can
have a pronounced effect on the adsorption and aggrega-
tion of SDDS. For example, compared with the SDDS/
TMAB (1:1), those parameters of the SDDS/Bolan (2:1),
including CMC, cCMC and C20, are different although the
both have identical ionic strength. Moreover, from Bola2Et
to Bola6, these parameters monotonously increase with
increasing n (Fig. 2), which well reflects the control of the
spacer length over the behavior of both adsorption and
aggregation [10].
From the minimum area (0.80 nm2) of SDDS occupied
at the interface in the absence of salts (see Table 1), one
can roughly estimate the radius (rsulfonate) of sulfonate
headgroup to be about 0.50 nm by the formula
prs2ulfonate ¼ Amin. By this way the electrostatic equilibrium
distance between the charge center of two sulfonate
headgroups is *1 nm (i.e. 2rsulfonate). On the other hand,
the stretched length of an alkanediyl spacer can be calcu-
lated by the formula ds/(nm) = 0.127(n ? 1), where n is
the number of methylene groups in the spacer. [12] Thus
the ds is 0.381 nm for Bola2Et, 0.635 nm for Bola4 and
0.889 nm for Bola6, respectively. These lengths are shorter
Method
Surface tension measurements were carried out with a
CHAN DCA-315 tensiometer equipped with a Pt–Ir du
Nou¨y ring. The circumference of the ring was 5.93 cm. The
ratio of the outside radius to the radius of the ring cross
section (R/r) was 53.1218. The error of surface tension
measurements was within 0.1 mN m-1
.
Results and Discussion
Effect of the Spacer of Bolaform Counterions
Figure 1 shows the semilogarithmic plots of the surface
tension (c) against the concentration (C) of surfactant
123

J Surfact Deterg
should be the reason that its CMC and C20 reduce rather
than rise compared with Bolan (n B 6).
As mentioned above, the added amount of Bolan coun-
terions is very small in the present systems. Even so, the
effect of the bolaform counterions is still very pronounced.
This is an important result because it confirms that even a
small amount of the Bolan is already sufficient to effec-
tively affect the adsorption and aggregation of ionic sur-
factants. This must mean that Bolan counterions can
associate strongly with SDDS. However, its monomer salt
(tetramethylammonium bromide, TMAB) cannot do it. The
data in Table 1 shows that for the system of SDDS/TMAB
(1:1), the CMC and C20 are close and even identical to that
of SDDS-alone. The strong interaction between the bola-
form counterions and the ionic surfactants is the pre-
requisite for constructing the gemini-like surfactants. How
to further enhance the interactions will be discussed in the
following section.
In addition to the active parameters mentioned above,
the surface excess and the corresponding area per molecule
occupied at the interface are also important parameters
reflecting the structure of the adsorption layer and the
ability of the controlling spacer. It is known that the
maximum surface excess of surfactant Cmax at the CMC
can be obtained by the Gibbs equation
Fig. 1 Semilogarithmic plots of the surface tension against the
surfactant concentration in aqueous bulk solution in the presence of
Bolan (including Bola2Et) counterions, in which the ratio of
surfactant to bolaform counterion is 2:1, while the ratio of SDDS to
TMAB is 1:1
than the electrostatic equilibrium distance between the two
sulfonate headgroups. This indicates that under the elec-
trostatic attraction of the bolaform counterions, SDDS
molecules can be pulled close together. This explains the
reduction in CMC and C20 for these systems compared
with that of SDDS-alone.
1
dc
2:303nRT d log C
C ¼ ꢁ
ð1Þ
where n is a constant depending on the number of
surfactant species. For conventional single-chain
surfactant, the value of n is 2. From Eq. (1), the
minimum area per molecule at the interface Amin can be
calculated by following formula
Bola12 has a spacer (1.65 nm) much longer than the
electrostatic equilibrium distance between the headgroups
of SDDS. The long and flexible alkanediyl spacer has been
known generally to bend toward the alkyl tails [10, 13–15],
which increases the density of hydrophobic moieties and
hence strengthens the attraction between alkyl tails. This
Amin ¼ 1=NACmax
where NA is the Avogadro constant.
ð2Þ
Table 1 Characteristic parameters derived from the surface tension plots of SDDS and SDDS/bolaform counterions
ꢁ0
ꢁ0
ads
System
CMC
(mmol L-1
cCMC
C20
(mmol L-1
Cmax
Amin
(nm2)
DG
DG
mic
(kJ mol-1
)
(kJ mol-1
)
)
(mN m-1
)
)
(lmol m-2
)
SDDS
7.4
37.6
40.2
35.9
38.9
39.2
37.1
39.2
32.1
32.5
34.1
34.5
1.86
1.86
0.57
0.74
0.79
0.15
0.88
0.11
0.13
0.13
0.037
2.08
2.02
2.15
2.10
2.08
1.64
2.90
2.56
2.07
2.03
1.66
0.80
0.82
0.77
0.79
0.80
1.0
-2.0
-2.3
-3.3
-3.2
-3.0
-4.4
-3.3
-4.7
-4.3
-4.0
-5.4
-18.1
-18.3
-20.6
-20.2
-20.2
-26.7
-17.3
-23.1
-24.7
-24.9
-30.2
SDDS/TMAB (1:1)
SDDS/Bola2Et (2:1)
SDDS/Bola4 (2:1)
SDDS/Bola6 (2:1)
SDDS/Bola12 (2:1)
SDDS/BTMAB (1:1)
SDDS/Bola2ph (2:1)
SDDS/Bola4ph (2:1)
SDDS/Bola6ph (2:1)
SDDS/Tetra6 (4:1)
5.7
2.2
2.5
2.8
0.76
2.1
0.58
0.64
0.80
0.82
1.0
0.55
0.83
1.1
0.28
123

J Surfact Deterg
Fig. 2 The CMC and C20 as a
function of the number of
methylene groups in the spacer
of bolaform counterions:
Bolan and Bolanph (n B 6)
From Table 1, the Amin values for Bolan (n B 6) are
smaller than that of SDDS-alone and that in the presence of
TMAB, show more close packing of SDDS molecules at
the interface. As discussed above, this benefits from the
inducement of the bolaform counterions with a spacer shorter
than the electrostatic equilibrium distance between the sul-
fonate headgroups. Reasonably, the Amin for Bola12 has a
relatively large value (1.0 nm2) since it has a quite long
spacer even though the spacer can bend toward the alkyl tails.
The standard free energy of micellization, DGꢁm0 ic, is
related to the CMC by the following formula [11]:
ꢁ0
importance and hence needs to be strengthened as far as
possible. At first sight, this seems very simple but it is
really rather complicated in the field of colloid, polymer,
and interface science. The most typical finding is the so-
called ‘Hofmeister series’ of the salt-effects as revealed
more than a century ago, which was found to relate to
many factors such as ionic hydration, size, polarity and
quantum electronic level, etc [16, 17]. By different influ-
ences of ions on the water structure, water-structure-mak-
ing or water-structure-breaking, the ions can be classified
into two types: cosmotropic (salting-out) ions and chao-
tropic (salting-in) ions [17]. The interaction between the
identical types of ions is expected to be strong, for exam-
ple, the interaction between cosmotropic/cosmotropic ions
or chaotropic/chaotropic ions [18]. In the present work, the
alkyl sulfonate and alkyl quaternary ammonium all belong
to chaotropic ions [16, 18], which favors exhibiting a
strong interaction. Moreover, compared with alkyl sulfate
ions used in the previous work [10] the alkyl sulfonate ions
can interact more strongly with the alkyl quaternary
ammonium ions according to the Hofmeister series [16].
These choices result in a pronounced effect of the bolaform
counterions in the present systems.
DG ¼ RTK0 lnðCMC=xÞ
ð3Þ
mic
where K0 is the degree of counterion association and 0.41
for SDDS as measured by conductivity method (the plot is
not shown), x is the number of moles of H2O per cubic
decimeter for pure water at the absolute temperature
T (x = 55.5 mmol dm-3 at 25 °C). In addition, the
standard free energy of adsorption at the surface pressure
p, DGꢁa0ds, follows the formula:
ꢁ0
DG ¼ RT lnðCw;p=xÞ ꢁ pNAAmin
ð4Þ
ads
At p = 52 mN m-1 (corresponding surfactant concen-
tration is C20), DGꢁa0ds can relate to the pC20 (= -logC20)
Even so, we still hope to further strengthen their inter-
actions using other approaches. In a previous paper,
we reported another series of bolaform counterions,
i.e. alkanediyl-a,x-bis(benzyldimethylammonium bromide)
(abbreviated as Bolanph) which all contain the aromatic
ring on the each side of the quaternary ammonium groups
(see Experimental). When this series of the counterions
interact with the anionic surfactants in the adsorption layer
or the aggregate, the attached aromatic rings can penetrate
into the palisade layers of surfactants, which were also
confirmed by NMR measurements in our previous work
[10]. This behavior is analogous to sodium salicylate as
promoter in the cationic micellar growth [19–21] and can
and the Amin
:
ꢁ0
DG ¼ ꢁ2:303RTðpC20;w þ log xÞ ꢁ 20NAAmin
ð5Þ
ads
The calculated thermodynamic parameters are also listed in
Table 1.
Enhancing Associating Force
As pointed out above, in the process of constructing
gemini-like molecules, the electrostatic attraction between
bolaform counterions and ionic surfactants is of utmost
123

J Surfact Deterg
provide an additional force to associate the bolaform
counterions with the surfactants besides the electrostatic
attraction. Compared with the Bolan-series, the Bolanph
with identical space length leads to smaller CMC and C20
(Fig. 2; Table 1). This again indicates that a strong inter-
action between the bolaform counterions and the ionic
surfactants favors to better achieve the dimerization of
active molecules (Fig. 3).
Oligomerization Test
Besides the effort made for the construction of gemini-
like (dimeric) surfactants utilizing the electrostatic
attractions, the preparation of oligomeric active-units is
also interesting. For this purpose we synthesized a tet-
rameric counterion (abbreviated as Tetra6), whose
chemical structure is described in the Experimental sec-
tion, intended to play the role of one Tetra6 attracting
four SDDS ions. Figure 4 is its surface tension plot, in
which the ratio of SDDS to Tetra6 is kept at 4:1. The
characteristic parameters concluded in Table 1 show that
in the presence of Tetra6, the activity of the system is
greatly enhanced. The CMC and C20 of SDDS/Tetra6 are
one order of magnitude smaller than that of SDDS/Bola6
or SDDS/Bola6ph, for which the spacer of all the coun-
terions are the same hexanediyl.
Fig. 4 Surface tension plot of mixed SDDS/Tetra6 (4:1) aqueous
solution
between the bolaform counterions and the ionic surfac-
tants. In the presence of simple salt TMAB (keeping the
ratio of 1:1 for SDDS to TMAB), the Amin (0.82 nm2)
reflects the electrostatic equilibrium result between the
SDDS molecules at the interface. For SDDS/BTMAB
(1:1), the Amin is only 0.58 nm2, which even includes the
benzene rings penetrating into the palisade layers. This
result strongly suggests that under the inducement of
BTMAB, SDDS molecules pack at the interface very
tightly. For SDDS/Bola6 and SDDS/Bola6ph (the ratio of
SDDS to bola is 2:1, having the same ionic strength with
the above systems), however, the Amins are almost iden-
tical, i.e. 0.80 nm2 with Bola6 and 0.82 nm2 with
Bola6ph. This fact indicates that the spacer of the bola-
form counterion can effectively control the behavior of
SDDS adsorption at the air/water interface. Compara-
tively, the Amin (1.0 nm2) of SDDS/Tetra6 (4:1) is
slightly larger than that of both SDDS/Bola6 and SDDS/
Bola6ph. This indicates that the control of oligomeric
counterions over ionic surfactants is weaker than dimeric
ones. It is perhaps due to more molecular disturbance
when the length of bolaform counterion is increased,
which must weakens its associating with ionic surfac-
tants. Therefore, it may be more difficult for the con-
struction of an oligomeric active-molecule than of a
dimeric molecule when mainly depending on the elec-
trostatic attractions.
The analysis for the minimum area of SDDS occupied
at the interface can help us to understand the interaction
Fig. 3 Semilogarithmic plots of surface tension against surfactant
concentration in aqueous bulk solution in the presence of Bolanph
counterions, in which the ratio of surfactant to bolaform counterion is
2:1, while the ratio of SDDS to BTMAB is 1:1
Acknowledgments Support from the Fujian Provincial Natural Sci-
ence Foundation of China (2010J01038) is gratefully acknowledged.
123

J Surfact Deterg
15. You Y, Jiang R, Ling TT, Zhao JX (2009) Bending of the flexible
spacer chain of gemini surfactant induced by hydrophobic
interaction. Chinese J Chem 27:469–471
16. Vlachy N, Jagoda-Cwiklik B, Vacha R, Jungwirth P, Kunz W
(2009) Hofmeister series and specific interactions of charged
headgroups with aqueous ions. Adv Colloid Interface Sci 146:
42–47
17. Leontidis E (2002) Hofmeister anion effects on surfactant self-
assembly and the formation of mesoporous solids. Curr Opin
Colloid Interface Sci 7:81–91
References
1. Moroi Y, Matuura R, Kuwamura T, Inokuma S (1986) Anionic
surfactants with divalent gegenions of separate electric charge:
solubility and micelle formation.
113:225–231
2. Moroi Y, Matuura R, Kuwamura T, Inokuma S (1988) Heat of
micelle formation: effect of counterions with concentrated, dif-
fused, and separated electric charges. Colloid Polym Sci
266:374–379
J Colloid Interface Sci
18. Abezgauz L, Kuperkar K, Hassan PA, Ramon O, Bahadur P,
Danino D (2010) Effect of Hofmeister anions on micellization
and micellar growth of the surfactant cetylpyridinium chloride.
J Colloid Interface Sci 342:83–92
19. Shikata T, Hirata H, Kotaka T (1987) Micelle formation of
detergent molecules in aqueous media: viscoelastic properties of
aqueous cetyltrimethylammonium bromide solutions. Langmuir
3:1081–1086
20. Shikata T, Hirata H, Kotaka T (1988) Micelle formation of
detergent molecules in aqueous media. 2. Role of free salicylate
ions on viscoelastic properties of aqueous cetyltrimethylammo-
nium bromide-sodium salicylate solutions. Langmuir 4:354–359
21. Clausen TM, Vinson PK, Minter JR, Davis HT, Talmon Y, Miller
WG (1992) Viscoelastic micellar solutions: microscopy and
rheology. J Phys Chem 96:474–484
3. Moroi Y, Matuura R, Tanaka M, Murata Y, Aikawa Y, Furutani
E, Kuwamura T, Takahashi H, Inokuma S (1990) Anionic sur-
factants with divalent counterions of separate electric charge. 2.
Micellar size and surface activity. J Phys Chem 94:842–845
4. Moroi Y, Matuura R, Yonemitsu T (1991) Anionic surfactants
with divalent counterions of separate electric charge. III. proton
NMR study. Bull Chem Soc Jpn 64:3094–3097
5. Moroi Y, Murata Y, Fukuda Y, Kido Y, Seto W, Tanaka M
(1992) Solubility and micelle formation of bolaform-type sur-
factants: hydrophobic effect of counterion.
96:8610–8613
J Phys Chem
6. Yamabe T, Moroi Y (1999) Micelle formation of anionic sur-
factant with divalent counterion of separate electric charge.
J Colloid Interface Sci 215:58–63
7. Masuda J, Nakahara H, Karasawa S, Moroi Y, Shibata O (2007)
Solution properties of perfluorinated anionic surfactants with
divalent counterion of separate electric charges. Langmuir
23:8778–8783
8. Matsumoto Y, Nakahara H, Moroi Y, Shibata O (2007) Langmuir
monolayer properties of perfluorinated double long-chain salts
with divalent counterions of separate electric charge at the air-
water interface. Langmuir 23:9629–9640
9. Menger FM, Littau CA (1993) Gemini-surfactants: synthesis and
properties. J Am Chem Soc 113:1451–1452
Author Biographies
Jianxi Zhao received his B.A. from the Fuzhou University in 1982
and his Ph.D. from the Uppsala University, Sweden, in 1995. He has
been at Fuzhou University since 1996. He is now Professor of
Chemistry and the member of the Colloid and Interface Chemistry
Committee of Chinese Chemistry Society. His current research
interests focus on self-assembly of oligomeric surfactants in semidi-
lute and concentrated solutions and their applications.
10. Yang D-P, Zhao J-X, Yang Y (2012) Langmuir monolayer
behavior of sodium hexadecyl sulfate controlled by bolaform
counterions. Colloids Surf A 396:258–263
11. Rosen MJ (1988) Surfactants and Interfacial Phenomena, 2nd ed.
Wiley, New York
12. Danino D, Talmon Y, Zana R (1995) Alkanediyl-a,x-bis(di-
methyl-alkylammonium bromide) surfactants (dimeric surfac-
tants). 5. Aggregation and microstructure in aqueous solutions.
Langmuir 11:1448–1456
13. Alami E, Beinert G, Marie P, Zana R (1993) Alkanediyl-a,x-
bis(dimethylalkylammonium bromide) surfactants. 3. behavior at
the air-water interface. Langmuir 9:1465–1467
Duoping Yang received his B.A. from the Fuzhou University in
2008. He is currently pursuing his Ph.D. degree under the supervision
of Prof. J. Zhao.
Yi You received his B.A. from the Fuzhou University in 1985. He is
now Professor of Chemistry in Fuzhou University.
14. Chen XD, Wang JB, Shen N, Luo YH, Li L, Liu MH, Thomas RK
(2002) Gemini surfactant/DNA Complex monolayers at the air–
water interface: effect of surfactant structure on the assembly,
stability, and topography of monolayers. Langmuir 18:6222–6228
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