Synthesis and viscoelastic behavior of an anionic gemini surfactant in aqueous solution

Article abstract of DOI:10.1524/zpch.2010.5537

A novel anionic Gemini surfactant,sodium dialkylbenzene disulfonate with spacer of -C₃H₆-, was synthesized and confirmed by ¹HNMR,MS and IR. Such Gemini surfactant in dilute aqueous solution without additives was researche

Full text of DOI:10.1524/zpch.2010.5537

Z. Phys. Chem. 224 (2010) 1355–1362 . DOI 10.1524.zpch.2010.5537
© by Oldenbourg Wissenschaftsverlag, München
Synthesis and Viscoelastic Behavior of an
Anionic Gemini Surfactant in Aqueous Solution
1
1
By Huijue Wu1, Xigang Du2, Yao Lu1, , Xin Zhang and Zhengyu Yang
*
1
Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing
100190, China
2
School of Chemical Engineering & Pharmaceutics, Henan University of Science and
Technology, Luoyang, 471003, China
(Received January 16, 2010; accepted February 24, 2010)
Anionic Gemini Surfactant . Synthesis . Viscoelastic Properties .
Shear-thinning . Temperature Influence
A novel anionic Gemini surfactant, sodium dialkylbenzene disulfonate with spacer of -C3H6-,
was synthesized and confirmed by 1HNMR, MS and IR. Such Gemini surfactant in dilute
aqueous solution without additives was researched by rotational rheometer and exhibited special
viscoelastic behaviors and shear-thinning properties like entangled polymer solution. The influ-
ence of concentration and shear rate on viscosity and shear modulus has been studied and the
reason of enhancing viscosity has also been discussed.
1. Introduction
Gemini surfactants, made of two conventional surfactants units connected with
a spacer group on or near hydrophilic groups, exhibit many special properties,
compared to single chain conventional surfactants [1,2]. Anionic Gemini surfac-
tants solutions with high viscosity are rarely researched, especially for the solu-
tions at low concentration without any additives, although much more attention
has been paid to cationic Gemini surfactants with short spacers, which make the
solution systems express high viscosity [3–5]. The anionic Gemini surfactant we
studied is dialkylbenzene disulfonate, in which two single-chain alkylbenzene
sulfonate surfacants (CnH2n+1C6H5SO3KNa+) are linked near the benzene groups
by -CmH2m-, marked as n-m-n, Fig. 1. Parts of this kind Gemini surfactants with
n = 6, 8, 10, 12, 14, m = 4, 6 have been synthesized and reported before in our
former work [6], but surfactants with m < 4 can not be synthesized by the
*
Corresponding author. E-mail: yaoluipc@yahoo.com.cn
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Fig. 1. Chemical structure of the studied anionic Gemini surfactant n–m–n.
same synthesis route [6]. Therefore, another new synthesis route was designed
to synthesize sulfonate Gemini surfactants with spacer group length m < 4. And,
in this article Gemini surfactant with shorter spacer m = 3 and alkyl chain length
n = 15 (15–3–15) was synthesized by this new optimized synthesis route, shown
in Scheme 1. Viscoelastic behavior was observed when it solved in aqueous
solution, and rheological properties of the solution at different concentrations
were studied by rotational rheometer at steady shear model and oscillating shear
model, in comparison with polymer aqueous solution.
2. Experiment and method
2.1. Synthesis of alkylbenzene sulfonate Gemini surfactant 15–3–15
The structure and synthesis method of sodium dipentadecyl dibenzene disulfo-
nate with n = 15, m = 3, marked 15–3–15, are showed in Scheme 1. The main
1
resultants through the synthesis are confirmed by HNMR and MS, such as 1,
5-Diphenyl-1, 5-pentanedione, dipentadecyldibenzene, and the final products 15–
3–15 (IR: 3040.23 cmK1(Ar-H); 2919.36, 2851.24 cmK1(-CH2-, -CH3); 1601.54,
1580.00, 1496.01, 1467.13 cmK1(Ar-C); 1194.34, 1130.90, 1042.36 cmK1(S =
1
O); 832.45 cmK1(p-Ar). HNMR (400MHz, D2O, δ in ppm): 7.60 (d, 4H), 7.00
(d, 4H), 2.30 (m, 2H), 1.14–1.80 (m, 58H), 0.92 (t, 6H). ESI-MS (negative): m.
z = 775.6 [M-2Na+H]K, m.z = 797.6 [M-Na]K.).
2.2. Viscoelastic property measurement
At first, transparent Gemini surfactant 15–3–15 solutions at different concentra-
tions and 0.25 wt% HPAM (Hydrolytic polyacrylamide, molecular weight of
7
!
1.2 10 ) solution were prepared in triply distilled water by warmly heating.
2.2.1 Shear-thinning measurements
The steady shear viscosity of 0.01 mol.L 15–3–15 solution and 0.25 wt% HPAM
solution were measured at different shear rate by using concentric cylinder rota-
tional rheometer, Brookfield R.S plus Rheometer (rotor of CC 48) , with shear
rate control state at room temperature about 30 °C.
2.2.2 Oscillating shear measurements
The oscillating rheological measurements on 15–3–15 solution were carried out
on a stress-controlled cone-plate rheometer (Haake MARS II). The cone and
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Synthesis and Viscoelastic Behavior
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Scheme 1. Synthesis route of dipentadecyldibenzene disulfonate surfactant 15–3–15.
plate are made of Titan steel with a diameter of 60 mm and a cone angle of 1°.
The gap between the center of the cone and plate is 0.045 mm and 1 mL sample
is needed for a test. The temperature was kept at 30 °C throughout the experi-
ments.
3. Result and discussion
3.1. Viscoelastic behavior
“Weissenberg effect”(the climbing of a viscoelastic liquid up a rotating rod) was
observed when stirring at 800 rpm, compared with distilled water at the same
rotate speed, which fell down the rotating rod, white arrow in Fig. 2. “Weissen-
berg effect” is a common phenomenon that occurs in polymer aqueous solution
or liquid polymer. The reason for this behavior is that the stresses in the direction
of the streamlines and in a direction normal to the streamlines is not equal. The
difference between these stresses causes the Gemini micelle solution to climb
the rotating rod. “Weissenberg effect” phenomenon was observed before in few
mixture surfactants system such as cetyltrimethyl ammonium hydroxide and 2-
hydroxy-1-naphthoic acid solution where rod-like micelles were forming [7],
this special phenomenon of pure dilute Gemini surfactant was scarcely studied.
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H. Wu et al.
Fig. 2. “Weissenberg effect” 0.01 mol.L Gemini surfactant 15–3–15 aqueous solution (right),
compared with distilled water (left) at 800 rpm stirring at the room temperature about 30 °C.
“Weissenberg effect” of surfactant 15–3–15 solution indicates its viscoelastic
property like polymer aqueous solution.
Different from conventional single chain alkylbenzene sulfonate surfactant
solutions with viscosity like water, Gemini surfactant 15–3–15 with short spacer
of -C3H6- solutions show high viscosity at low concentrations like polymer solu-
tions. According to former research of some conventional single chain cationic
surfactant systems mixed with salt [8,9] or some cationic Gemini surfactants
with short spacer group [3–5], the viscoelastic behavior of solution is contributed
to wormlike micelles formed and entangled in solutions. The molecular packing
parameter P is often used to predict shape of aggregate of the surfactant in
solution [10,11]. When P = 1.3–1.2, wormlike micelles or entangled micelles
are formed. For Gemini surfactant, shorter spacer groups induce P to satisfy
proper value and make wormlike micelles form in solution without any other
additive. Wormlike micelles can be observed and confirmed by TEM or cryo-
TEM [12–15]. The high viscosity of studied alkylbenzene sulfonate Gemini sur-
factant solution system is also probably due to entangled wormlike or netlike
micelles formed in solution system.
3.2 Shear-thinning behaviour
The viscosity of Gemini solution and polymer solution depending on shear rate
is show in Fig. 3. Unlike water, the viscosity of both solutions decreases rapidly
along with increasing of shear rate in log axis. Fluid model equation
(1)
where η is apparent viscosity and γ is shear rate, and its transformation
(2)
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Synthesis and Viscoelastic Behavior
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Fig. 3. Dependence of viscosity on shear rate at temperature of 30°C.
can be used to character this non-Newton fluid behavior. Both anionic Gemini
surfactant and polymer solution can fit this formula, so we can calculator the
constant value of K = 734.01, n = 0.184 for 15–3–15, and K = 2084.49, n = 0.199
for polymer solution. K indicates how viscous the solution is and n indicates the
fluid property. Higher K value means higher viscosity, and the more deviation
of n from 1 (value of water) means stronger non-Newton fluid behavior of the
solution. The shear-thinning behavior may results from the microstructure change
of micelles in this anionic Gemini surfactant solution.
3.4. Oscillating shear measurements
A strain sweep was performed at a frequency of 1Hz (6.28 rad sK1) before the
test to make sure that the sample was in the linear viscoelastic region during
oscillatory measurements. There is no linear viscoelastic region for the solutions
until the concentration reaches 0.0025 mol.L, above which the stress is constant
at 0.1 Pa during the oscillating measurements.
Elastic modulus G’ (storage modulus) and viscous modulus G” (loss modu-
lus) of 15–3–15 solutions at different concentrations are shown in Fig. 4. Both
modulus increase with increasing concentrations, and for the 15–3–15 solution
at 0.0025 mol.L, the viscous modulus G” is always above the elastic modulus
G’ in the examined frequencies range, while G” is always below G’ for the
solution at 0.05 mol.L, which shows very strong elastic behavior. The two mod-
ulus cross in the case of 0.005 and 0.01 mol.L solutions, and the sample exhibits
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H. Wu et al.
Fig. 4. Variations of G’ (filled symbols) and G” (open symbols) with frequency f in 15–3–15
solutions at different concentrations. The symbols represent 0.0025 mol.L (triangles),
0.005 mol.L (rectangles), 0.01 mol.L (pentacle) and 0.05 mol.L (circle), respectively.
elastic behavior at high frequency f , whereas at low f the sample shows a viscous
behavior (G” exceeds G’).
Besides, the complex viscosity -η*- for surfactant solutions can also be meas-
ured simultaneously, shown in Fig. 5. Almost all the studied solutions fit Max-
well fluid model [16–17]. -η*- decreases rapidly at high frequency, and reaches a
plateau value at low frequency. Thus the zero-shear viscosity η0 can be obtained
by extrapolating f to the ordinate at f
= 0 (ω = 2π f = 0) [17]. With the
increasing concentrations of 15–3–15 solutions, Zero-shear viscosity η0 increase
slowly at first and then rapidly, which is shown in Fig. 6. The increasing viscos-
ity of solution is contributed to more and more wormlike micelles formed and
entangled in solutions, but this surfactant won’t dissolve well above concentra-
tion of 0.05 mol.L at 30 °C.
4. Conclusions
The novel anionic Gemini surfactant with shorter spacer group (-C3H6-) was
1
synthesized by a new method and confirmed by IR, HNMR and ESI-MS. This
anionic Gemini surfactant exhibits special viscoelastic property in dilute solution
without additives like polymer aqueous solution. “Weissenberg effect” is ob-
served, which indicates the viscoelastic property of the system. The steady shear
viscosity and zero-shear viscosity of solution increase with the concentration
growing up and the shear-thinning curves can fit non-Newton fluid model. The
15–3–15 solutions exhibit higher elastic or storage modulus at high concentration
at high frequency than viscous or loss modulus, or vice versa.
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Synthesis and Viscoelastic Behavior
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Fig. 5. The complex viscosity -η*- as a function of frequency f for 15–3–15 solutions at different
concentrations.
Fig. 6. Zero-shear viscosity η0 as a function of concentration of 15–3–15 aqueous solution.
Acknowledgement
We are grateful for the financial support from the National Natural Science
Foundation of China (Grant No. 20953004) and the Doctor Fund Project of
Shandong Province (BS2009SF019).
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