Synthesis and properties of a series of CO2 switchable surfactants with imidazoline group

Article abstract of DOI:10.1007/s11743-012-1332-5

Switchable surfactants are environment-friendly compounds, which can be separated from the system or lose surface activity after completing their function during one stage of a process. In order to study switchable properties of a kind of CO₂ switchable surfactant with an imidazoline group, four 2-alkyl-1-hydroxyethylimidazolines were synthesized by condensation of N-(2-hydroxyethyl)ethanediamine with dodecanoic, tetradecanoic, hexadecanoic, and octadecanoic acids. Then, the series of long-chain alkyl imidazoline compounds were reacted with dry ice to produce imidazolinium bicarbonates cationic surfactants. The critical micelle concentration (CMC) and surface tension at CMC (γ_cmc) measured by the Wilhelmy plate technique show that these surfactants have excellent surface activity. The changes of conductivity before and after bubbling CO₂ show the conversion between imidazolines and imidazolinium bicarbonates cationic surfactants. Conductivity cycles indicated that these surfactants could be switched by CO₂ reversibly and repeating this three times. However, their switchable function on the emulsification-demulsification of water-alkane was dissatisfactory due to the emulsibility of amide which was hydrolyzed from 2-alkyl-1-hydroxyethylimidazoline. Therefore, the application of these switchable surfactants needed to be studied further.

Full text of DOI:10.1007/s11743-012-1332-5

J Surfact Deterg (2012) 15:533–539
DOI 10.1007/s11743-012-1332-5
ORIGINAL ARTICLE
Synthesis and Properties of a Series of CO2 Switchable
Surfactants with Imidazoline Group
•
Weihong Qiao Zhibo Zheng Qingzhao Shi
•
Received: 3 September 2011 / Accepted: 16 January 2012 / Published online: 5 February 2012
Ó AOCS 2012
Abstract Switchable surfactants are environment-friendly
compounds, which can be separated from the system or lose
surface activity after completing their function during one
stage of a process. In order to study switchable properties of a
kind of CO2 switchable surfactant with an imidazoline
group, four 2-alkyl-1-hydroxyethylimidazolines were syn-
thesized by condensation of N-(2-hydroxyethyl)ethanedia-
mine with dodecanoic, tetradecanoic, hexadecanoic, and
octadecanoic acids. Then, the series of long-chain alkyl
imidazoline compounds were reacted with dry ice to produce
imidazolinium bicarbonates cationic surfactants. The critical
micelle concentration (CMC) and surface tension at CMC
(ccmc) measured by the Wilhelmy plate technique show that
these surfactants have excellent surface activity. The chan-
ges of conductivity before and after bubbling CO2 show the
conversion between imidazolines and imidazolinium bicar-
bonates cationic surfactants. Conductivity cycles indicated
that these surfactants could be switched by CO2 reversibly
and repeating this three times. However, their switchable
function on the emulsification-demulsification of water-
alkane was dissatisfactory due to the emulsibility of amide
which was hydrolyzed from 2-alkyl-1-hydroxyethylimi-
dazoline. Therefore, the application of these switchable
surfactants needed to be studied further.
Introduction
Surfactants are used to stabilize emulsions in cleaning,
emulsion and microsuspension polymerization, viscous oil
transportation, cosmetics and so on. However, an emulsion is
only useful during one stage of a process, after which the
surfactants are hoped to be separated from the system or lose
surface activity. Switchable surfactants, which can undergo
fully reversible interconversions between active and inactive
forms, could be used to solve this problem in a satisfactory
way. Moreover, it is important for the reuse of switchable
surfactants between emulsification and demulsification to
reduce the application cost to some extent and decrease any
environment pollution. Thus a switchable surfactant is a kind
of environmentally friendly compound [1, 2].
In 2006, Liu et al. [3] reported a series of N0-alkyl-N,N-
dimethylacetamidines which can be repeatedly switched
‘‘on’’ and ‘‘off’’ as necessary (see Scheme 1, where R is
long-chain alkyl). By bubbling through carbon dioxide, the
N0-alkyl-N,N-dimethylacetamidines produced N0-alkyl-
N,N-dimethylacetamidinium bicarbonates cationic surfac-
tants. By bubbling air, nitrogen, argon or another inert
gas under heating, the reverse reaction occurred to produce
the original N0-alkyl-N,N-dimethylacetamidines. Carbon
dioxide and air (or nitrogen, inert gas) trigger the switching
of the surfactants. This indicates that these surfactants can
control system stability as necessary, besides possessing
basic properties of classical surfactants, such as emulsifi-
cation and foaming. In 2009, Qin Yong et al. [4] studied
the preparation and reversible performance of dodecyl
tetramethyl guanidine as a CO2-switchable surfactant.
Other researchers studied switchable properties of many
compounds with an amidine group and a guanidine group
[5–10], though they reported them as switchable solvents,
rather than switchable surfactants.
Keywords Switchable surfactants ꢀ CO2 ꢀ
Emulsification ꢀ Reversibility
W. Qiao (&) ꢀ Z. Zheng ꢀ Q. Shi
State Key Laboratory of Fine Chemicals, School of Chemical
Engineering, Dalian University of Technology, Dalian 116023,
People’s Republic of China
e-mail: qiaoweihong@dlut.edu.cn
123

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J Surfact Deterg (2012) 15:533–539
Me
(HP America, model HP1100LC/MSD). NMR analysis was
carried out with a Bruker 400 MHz instrument (Bruker,
France, Model AVANCEII 400 MHz). IR analysis was
carried out with a FT-IR spectrometer (Thermo Nicolet,
America, Model NEXUS). The melting point was mea-
sured by X-4 melting point apparatus (Ningbo Yongxin
Optical Co. Ltd.). The surface tension was determined with
a processor tensiometer (Kru¨ss, Germany, Model K100C)
by the Wilhelmy plate technique. The conductivity was
measured by a DDSJ-308A conductivity meter (Shanghai
Hongyi Instrument Co. Ltd.). The emulsion was prepared
in the ultrasonic bath KH-300DB (Kunshan Hechuang
Ultrasonic Instrument Co. Ltd).
Me
CO2
R
+
H2O
HCO3
R
N
NMe2
-CO2
N
NMe2
H
Scheme 1 The ‘‘on’’ and ‘‘off’’ of switchable surfactants
It was conjectured that long-chain alkyl imidazoline
would be a kind of switchable surfactant which could be
triggered byCO2 due to the N=C–N in theimidazoline. Many
references were found about the synthesis of imidazolines
[11–13]. In this work, a series of long-chain alkyl imidazo-
lines were synthesized, and their surface activities and
switchable performance triggered by CO2 were reported.
Synthesis
Experimental Procedures
The synthesis routes of long-chain alkyl imidazolines and
long-chain alkyl imidazolinium bicarbonates are shown in
Scheme 2 and Scheme 3, respectively. For a succinct
description, the 2-alkyl-1-hydroxyethylimidazolines are
recorded as a, as shown in Scheme 3. Different imidazo-
lines are called 1a, 2a, 3a, and 4a according to their dif-
ferences in the carbon chain. Correspondingly, their
bicarbonates are named as b. Thus different imidazolinium
bicarbonates are recorded as 1b, 2b, 3b, and 4b according
to their differences in the carbon chain.
General
Dodecanoic, tetradecanoic, hexadecanoic and octadecanoic
acids were purchased from Tianjin Guangfu Fine Chemi-
cals Research Institute, China. N-(2-hydroxyethyl) ethane
diamine was purchased from the Sinopharm Chemical
Reagent Co. Ltd., China. Ethyl ether was purchased from
the Tianjin Fuyu Fine Chemical Co. Ltd., China. Dodecane
was purchased from the Tianjin Kemio Chemical Co. Ltd.,
China. Tetrahydrofuran (THF) and xylene were purchased
from the Tianjin Bodi Chemical Co. Ltd., China. Deionized
water was used in all measurements.
Synthesis of 2-Alkyl-1-Hydroxyethylimidazolines
The mass spectrum was obtained with a High Perfor-
mance Liquid Chromatography/Mass selective Detector
A three-necked flask equipped with a stirrer, a thermom-
eter, a reflux condenser and a water segregator was charged
Scheme 2 Synthesis route of
long-chain alkyl imidazolines
O
H
N
H2N
N
220
140
R
C
R
COOH
R
+
HN
CH2CH2OH
N
HN
CH2CH2OH
CH2CH2OH
R= C11H23, C13H
27, C15H
31, C17H35
H
N
Scheme 3 Synthesis route of
long-chain alkyl imidazolinium
bicarbonates
N
N
HCO3
R
+
+
R
H2O
CO2
N
CH2CH2OH
CH2CH2OH
1a R=C11H23
1b
2b
3b
4b
2a
3a
4a
R=C13H27
R=C15H31
R=C17H35
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J Surfact Deterg (2012) 15:533–539
535
1014
with 11.4 g (0.05 mol) of tetradecanoic acid, 6.76 g
(0.065 mol) of N-(2-hydroxyethyl)ethanediamine and
30 mL of xylene. The reactant was refluxed at 140 °C until
no more water came over from the water separator (about
4 h). Then, the xylene was removed from the flask through
the water separator, and the reaction temperature increased
to 220 °C for another 4 h. After cooling the mixture to
room temperature, the brown solid obtained was crushed
and washed three times with ethyl ether to give 13.16 g of
a white solid (2-tridecyl-1-hydroxyethylimidazoline). The
yield was found to be 88.9%. Other 2-alkyl-1-hydro-
xyethylimidazolines were obtained in the same way. The
yields of 1a, 3a and 4a were 72.9, 85.2 and 89.6%,
respectively.
Am
¼
ð2Þ
NCm
The solutions of 2-alkyl-1-hydroxyethyl imidazolinium
bicarbonates were made with CO2-saturated water, and
CO2 was bubbled through each solution again for 2 min
immediately before the measurement.
Emulsion Stability Tests
Twenty milligrams of 2-alkyl-1-hydroxyethyl imidazolin-
ium bicarbonates, 2 mL of deionized water and 2 mL of
dodecane were added to a 10-mL stoppered tube. Then
the stoppered tube was vibrated ultrasonically at 32 kHz
at 25 °C in the ultrasonic bath for 30 min and the
emulsion was formed. The emulsion stability was deter-
mined by observing the emulsion separation at room
temperature after 5, 10, 30 min, 1, 2, 3 h, 1 and 2 days,
respectively.
Synthesis of 2-Alkyl-1-Hydroxyethylimidazolinium
Bicarbonates
Dry ice (20 g) was added gradually to 2-tridecyl-1-hydro-
xyethylimidazoline (1 g, 0.0034 mol) dissolved in THF.
After filtration, the white solid, 2-tridecyl-1-hydroxyethyl
imidazolinium bicarbonate (0.86 g, 72.8%) was obtained.
Other 2-alkyl-1-hydroxyethyl imidazolinium bicarbonates
were obtained in the same way. The yields of 1b, 3b and 4b
were 75.2, 69.0 and 65.4%, respectively.
Switching Performance
1. A 0.1-g quantity of 2a was dissolved in 40 mL of
undried DMSO. CO2 was bubbled through the liquid at
a rate of several bubbles per second at 23 °C. The
conductivity of the liquid was measured with a con-
ductimeter at 30-s intervals from the beginning until
the conductance value was stabilized. Then N2 was
bubbled through the liquid until the conductivity
reached the starting value. This CO2 (and then N2)
treatment was performed for a total of three cycles.
2. A mixture of 2 mL of dodecane, 2 mL of water and
20 mg of 2b were ultrasonically vibrated at 32 kHz at
25 °C in the ultrasonic bath for 30 min and the
uniform emulsion was obtained. Then the prepared
emulsion was heated to 70 °C with bubbling N2 for 3 h
to break the emulsion.
Conductivity Measurements
2-alkyl-1-hydroxyethyl imidazolines and 2-alkyl-1-hydro-
xyethyl imidazolinium bicarbonates were prepared into
0.1% aqueous solution with deionized water. Their con-
ductivities were measured with DDSJ-308A conductivity
meter at 23 °C, respectively.
Determination of CMC, ccmc, Cm and Am
The surface tension at different concentrations of 2-alkyl-
1-hydroxyethyl imidazolinium bicarbonates solutions was
measured by the Wilhelmy plate technique at 25 °C. All
surface tension values shown are averages of two mea-
surements. The CMC and ccmc were determined from
the breakpoint of the plot of surface tension of their
aqueous solutions versus concentration. The surface
excess concentration (Cm) was obtained from the Gibbs
equation (Eq. 1), where R is the ideal gas constant
(8.314 J mol-1 K-1), and dc/dlgC is the slope of the plot
of surface tension versus logarithm of the surfactant con-
centration. The area per surfactant molecule (Am) at the air/
water surface was estimated from Eq. 2, where N is Avo-
gadro’s constant.
Results and Discussion
Synthesis and Characterization
The 2a imidazoline was dissolved in chloroform and ana-
lyzed by a Mass Selective Detector (MSD). The mass
spectrum shows peaks of the target product at m/z 297.2530
(M ? H?) and m/z 593.5247 (2M ? H?). The NMR
spectrum was measured in CDCl3. The 1H NMR: 0.88
(t, 3H, CH2CH3), 1.25 (s, 20H, (CH2)10CH3), 1.62 (m, 2H,
CH2(CH2)10CH3), 2.18 (t, 2H, CH2C=N), 2.78 (t, 4H,
CH2NCH2), 3.36 (t, 2H, C=NCH2), 3.67 (t, 2H, CH2OH),
5.91 (–OH). The IR spectrum of 2a showed a broad O–H
band at 3,405.84 cm-1 as well as strong absorption of
ꢀ
ꢁ
ꢁ1
dc
2:303RT d lg C
Cm
¼
ð1Þ
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J Surfact Deterg (2012) 15:533–539
1b: IR: m(O–H) 3,421.55 cm-1, m(C=N) 1,605.91 cm-1
c (HCO3) 835.32 cm-1
3b: IR: m(O–H) 3,421.99 cm-1, m(C=N) 1,602.50 cm-1
c (HCO3) 837.76 cm-1
,
,
,
m(C=N) of imidazoline ring at 1,602.65 cm-1. The melting
point of 2a is 53.3–54.6 °C The spectra and melting points
of 2-alkyl-1-hydroxyethyl imidazolines were as follow:
.
.
1a: MS m/z 269.1866 (M ? H?) and m/z 537.3836
(2M ? H?). 1H NMR: 0.88 (t, 3H, CH2CH3), 1.25 (s, 16H,
(CH2)8CH3), 1.62 (m, 2H, CH2(CH2)10CH3), 2.18 (t, 2H,
CH2C=N), 2.78 (t, 4H, CH2NCH2), 3.36 (t, 2H, C=NCH2),
3.67 (t, 2H, CH2OH), 5.91 (–OH). IR: m(O–H)
3,442.41 cm-1, m(C=N) 1,605.49 cm-1. Melting point:
40.1–41.6 °C.
3a: MS m/z 326.2941 (M ? H?) and m/z 649.5624
(2M ? H?). 1H NMR: 0.88 (t, 3H, CH2CH3), 1.25 (s, 24H,
(CH2)12CH3), 1.62 (m, 2H, CH2(CH2)10CH3), 2.18 (t, 2H,
CH2C=N), 2.79 (t, 4H, CH2NCH2), 3.36 (t, 2H, C=NCH2),
3.67 (t, 2H, CH2OH), 6.00 (–OH). IR: m(O–H)
3,421.99 cm-1, m(C=N) 1,602.50 cm-1. Melting point:
62.3–63.5 °C.
4a: MS m/z 353.4098 (M ? H?) and m/z 705.7993
(2M ? H?). 1H NMR: 0.88 (t, 3H, CH2CH3), 1.25 (s, 28H,
(CH2)14CH3), 1.62 (m, 2H, CH2(CH2)10CH3), 2.18 (t, 2H,
CH2C=N), 2.79 (t, 4H, CH2NCH2), 3.37 (t, 2H, C=NCH2),
3.68 (t, 2H, CH2OH), 6.01 (–OH). IR: m(O–H)
3,383.37 cm-1, m(C=N) 1,604.32 cm-1. Melting point:
66.1–67.2 °C.
4b: IR: m(O–H) 3,395.44 cm-1, m(C=N) 1,604.32 cm-1
c (HCO3) 836.41 cm-1
.
Conductivity
2-Alkyl-1-hydroxyethyl imidazolines are neutral and
should not show surface activity. After adding CO2, they
are converted into 2-alkyl-1-hydroxyethyl imidazolinium
bicarbonates cationic surfactants that can be surface active.
The conductivities before and after addition of CO2 were
compared in Fig. 1.
Figure 1 indicates that 2-alkyl-1-hydroxyethyl imidaz-
olines converted into 2-alkyl-1-hydroxyethyl imidazolini-
um bicarbonates after the addition of CO2, resulting
conductivity varied greatly.
CMC, ccmc, Cm and Am
The CMC, ccmc, Cm and Am are important parameters for
surfactants. The surface tension of 1b * 4b at different
concentrations was measured by the Wilhelmy plate tech-
nique at 25 °C. The curve of surface tension versus the
logarithm of concentration (see Fig. 2) was drawn to obtain
CMC and ccmc and to calculate Cm and Am, which are
exhibited in Table 1.
In a previous work, it was reported that adding dry
ice to the solution of N0-alkyl-N,N-dimethyl acetamidines
can yield more N0-alkyl-N,N-dimethyl acetamidinium
bicarbonates than adding CO2 gas [14]. Therefore, in
this work, dry ice was used as the CO2 source when
2-alkyl-1-hydroxyethyl imidazolinium bicarbonates were
obtained.
Table 1 indicates that, from lb to 4b, the CMC gradu-
ally decrease with the increase of carbon number. The
ascending order of ccmc values were 2b \ 1b \ 4b \ 3b.
Heldebrant et al. [9] have reported that a kind of
liquid compound which contains an amidine and hydroxy
group adsorbed CO2 in the absence of water to obtain
zwitterionic liquids. Under this condition, CO2 coordi-
nated to alkoxide oxygen. Because the switchable sur-
factants would apply in aqueous solution or at the water–
oil interface, the water was not absent when long-chain
alkyl imidazoline reacted with CO2. The IR spectrum of
2b in KBr showed strong bands at 1,602.65 cm-1, which
are protonated amidine [C=N–H?]. A new band appeared
at 836.12 cm-1, which is comparable to another bicar-
bonate anion, such as [DBUH][HCO3] (836 cm-1) and
Emulsifying Capacity
Under the same conditions, the emulsion stability and
emulsifying capacity of 1b * 4b were evaluated by
observing the emulsion state at different times. Table 2
shows that the emulsion stability is in the following order
180
160
140
120
100
80
KHCO3 (835 cm-1) [15]. The free O–H (3,405.84 cm-1
)
60
40
was still detectable. Therefore, we conjectured that
2-alkyl-1-hydroxyethyl imidazolines reacted with CO2 to
yield 2-alkyl-1-hydroxyethyl imidazolinium bicarbon-
ates cationic surfactants other than zwitterionic sur-
factants when water was present. Other IR spectra of
2-alkyl-1-hydroxyethyl imidazolinium bicarbonates were
as follow:
20
0
11
13
15
17
Carbon numbers of R
Fig. 1 Conductivity changes before (black bar) and after (white bar)
addition of CO2
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J Surfact Deterg (2012) 15:533–539
537
bubbled alternately through the solution over three cycles,
shown in Fig. 3. The conductivity rose when CO2 was
bubbled through the solution, and it dropped upon N2
addition.
Generally, surfactants adsorb on the water–oil interface
to form an interfacial film. An interfacial film has a certain
resistance, which can prevent the droplet from aggregating
by collision under Brownian motion. So, the cationic sur-
factants, 2-alkyl-1-hydroxyethyl imidazolinium bicarbon-
ates (1b * 4b), can make the emulsion stable. Bubbling
N2 under heating, the cationic surfactant released CO2 to
convert to neutral long-chain alkyl imidazoline. The
emulsion should thus be broken. Therefore, we tried to
further confirm the switching ability of 2b by an emulsi-
fication-demulsification experiment. However, the result of
demulsification is not very significant. The formed emul-
sion only separated 0.2 mL of oil phase under heating at
70 °C with N2 bubbling for 3 h. It is speculated that the
neutral 2-alkyl-1-hydroxyethyl imidazoline could also
emulsify the water and oil phase. In order to demonstrate
this conjecture, the emulsification experiments were carried
out with 2a and 2b, respectively. The results are shown in
Table 3. It can be seen that 2a was able to make the water-
dodecane emulsion stable for more than 3 h, but less than
the emulsion prepared with 2b. It was reported that imi-
dazoline could be hydrolyzed to amide, and the rate of
hydrolysis was increased with strengthening of alkalinity of
aqueous solution [16]. As a kind of polar organic com-
pound, the long-chain alkyl amide which is surface-active
can also emulsify water and alkane [17]. It is conjectured
that the emulsifying abilities of 1a * 4a were from the
long-chain alkyl amide obtained by partial hydrolysis of
long-chain alkyl imidazoline. In order to verify this
hypothesis, 1 g of 2a with 0.5 mL of water was laid for
3 h, and then was vacuum dried to remove the water. In the
IR spectrum of the processed 2a, besides the strong
absorption peak of m(C=N) of the imidazoline ring at
1,604.71 cm-1, new bands appeared at 1,640.16 cm-1
Fig. 2 Surface tension versus logarithmic concentration curve of
1b * 4b
Table 1 The CMC, ccmc, Cm and Am of 1b * 4b
CMC/mol L-1
c
cmc/mN m-1
Cm/mol cm-2
Am/nm2
1b
2b
3b
4b
2.04 9 10-3
1.48 9 10-3
2.57 9 10-4
1.35 9 10-4
29.02
28.13
36.37
33.14
1.53 9 10-10
1.74 9 10-10
3.41 9 10-10
2.59 9 10-10
1.084
0.957
0.487
0.640
2b [ 1b [ 4b [ 3b, which is consistent with their capac-
ity of reducing surface tension (ccmc in the order
2b \ 1b \ 4b \ 3b). The emulsions that were prepared
with 1b and 2b respectively were both quite stable for more
than one day.
Switchable Performance
First of all, the reversibility and repeatability of the process
were confirmed by monitoring the conductivity of a solu-
tion of 2a in undried DMSO while CO2 and N2 were
Table 2 Evaluation of emulsion stability of 1b * 4b
Time
1b
2b
3b
4b
5 min
10 min
30 min
1 h
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
Phase separation (lower layer 0.2 mL)
Phase separation (lower layer 0.8 mL)
Phase separation (lower layer 1.3 mL)
Phase separation (lower layer 1.4 mL)
Phase separation (lower layer 1.6 mL)
Phase separation (lower layer 1.6 mL)
Phase separation (lower layer 1.7 mL)
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
Homogeneous emulsion
2 h
3 h
1 day
Phase separation
(lower layer 0.2 mL)
2 days
Phase separation
(lower layer 0.1 mL)
Homogeneous emulsion
Phase separation (lower layer 1.8 mL)
Phase separation
(lower layer 0.2 mL)
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J Surfact Deterg (2012) 15:533–539
1a * 4a can also reduce the surface tension of water, and
are thus surface-active. Therefore, this series of switchable
surfactants were not suitable for emulsification-demulsifi-
cation of water-alkane because of other changes taking
place. The application of these switchable surfactants thus
needs to be further studied. The results also showed that the
change of substituent position of alkyl from 2 to 4 on
imidazoline ring may overcome the weakness of hydrolysis
of 2-alkyl imidazoline.
Acknowledgments This work was supported by the PetroChina
Innovation Foundation (2009D-5006-02-12).
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Fig. 4 Surface tension versus logarithmic concentration curve of
1a * 4a
(m(C=O)) and 1,561.01 cm-1 (d(N–H) in –C(=O)N–H),
which indicated that the imidazoline partly hydrolyzed into
amide. The surface tensions of 1a * 4a at different con-
centrations (see Fig. 4) were measured. Figure 4 showed
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17. Xiao JX, Zhao ZG (2003) Principles of surfactants. Chemical
Industry Press, Beijing
Zhibo Zheng was born in 1985. He obtained his bachelor’s degree
from Henan University in 2004. He is now a candidate for a master’s
degree in the synthesis and physical chemistry of surfactants at Dalian
University of Technology.
Author Biographies
Qingzhao Shi was born in 1989. She obtained her bachelor’s degree
from Dalian University of Technology in 2011. She is now a
candidate for a master’s degree in the synthesis and physical
chemistry of surfactants at Dalian University of Technology.
Weihong Qiao was born in 1968. She obtained a master’s degree
from Dalian University of Technology in 1994 and a Ph.D. from the
same university in 2000. Since 1994, she has been teaching and
working at the Dalian University of Technology, Dalian, P. R. China.
Her main field of research is the synthesis and physical chemistry of
surfactants.
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