Coacervation of dynamic covalent surfactants with polyacrylamides: Properties and applications

Article abstract of DOI:10.1039/c8sm00773j

Dynamic covalent surfactants have been prepared from a mixture of 4-formyl-N,N,N-trimethylbenzenaminium iodide (FBA) with heptylamine (C₇A) or octylamine (C₈A) in alkaline aqueous solutions. The reversible pH-dependent nature of the

Full text of DOI:10.1039/c8sm00773j

View Article Online
View Journal
Soft Matter
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: W. Zhao, H. Wang
and Y. Wang, Soft Matter, 2018, DOI: 10.1039/C8SM00773J.
This is an Accepted Manuscript, which has been through the
Volume 12 Number
1 7 January 2016 Pages 1–314
Royal Society of Chemistry peer review process and has been
accepted for publication.
Soft Matter
Accepted Manuscripts are published online shortly after
www.softmatter.org
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1744-683X
PAPER
Jure Dobnikar et al.
Rational design of molecularly imprinted polymers
rsc.li/soft-matter-journal

Please do not adjust margins
Page 1 of 8
Soft Matter
View Article Online
DOI: 10.1039/C8SM00773J
Soft Matter
Paper
Coacervation of Dynamic Covalent Surfactant with
Polyacrylamide: Property and Application
Weiwei Zhao,ab Hua Wang,ab Yilin Wang*ab
Received 00th April 2018,
Accepted 00th April 2018
Dynamic covalent surfactants have been prepared from the mixture of 4-formyl-N, N, N-trimethylbenzenaminium iodide
(FBA) with heptylamine (C7A) or octylamine (C8A) in alkaline aqueous solutions. The reversible pH-dependent nature of
imine bond is characterized by 1H NMR and fluorescence analysis. The dynamic covalent surfactants self-assemble into
micelles in alkaline condition and form coacervation with 10% hydrolyzed polyacrylamide (PAM) over a wide concentration
range. The coacervate phase with a net-work structure was found to effectively extract anionic dye Conge Red (CR). When
the solution is adjusted to acidity, the imine bond is hydrolyzed, leading to the transition of coacervates into a
homogeneous and clear solution, and the precipitation of CR into purple-black solids due to the protonation of sulfonic
groups. Thus the extraction and release of CR molecules are realized with the dynamic covalent surfactant/PAM system.
Moreover the initial components, FBA, amine, and PAM, can be easily regenerated with hydrochloric acid. This method
shows potential applications in wastewater treatment.
DOI: 10.1039/x0xx00000x
www.rsc.org/
organic compounds.
Introduction
Dynamic covalent surfactants switch the structure and
property of surfactants between amphiphilic and non-
Coacervation, i.e. liquid-liquid phase separation, is
a
amphiphilic characteristics by utilizing dynamic covalent bonds,
which convert between covalent bonds and non-covalent
spontaneous formation of two immiscible liquid phases in a
colloidal dispersion: a dense coacervate phase and a diluted
phase.1,2 Coacervation has attracted
bonds under
a
certain stimulus.19-23 Stimulus-responsive
a growing interest
dynamic covalent bonds include hydrazones, imines (Schiff
bases), disulfides, acetals, carboxylic and boronic esters.24
Imine bonds display good product stability and fast kinetics
under mild reaction conditions, forming in neutral or basic
solutions but being hydrolyzed under weakly acidic condition.
Thus imine bonds have been widely used as dynamic covalent
bonds to constructing diverse functional surfactants. Nguyen
et al.25, 26 fabricated nonionic dynamic covalent surfactants by
the condensation of a p-substituted benzyl aldehyde with a
hydrophobic tail and aliphatic, benzylic, aromatic, and hydroxy
amines, which show different equilibrium constants and self-
assembled structures. The group of van Esch27 reported a
cationic dynamic covalent surfactant which utilizes an imine
bond to link aromatic aldehyde and alkyl amine of different
chain length, and found that the micellization of the surfactant
is responsive to pH and temperature. The surfactant is stable
under mild basic conditions, but dissociated into a non-
aggregated and non-amphiphilic state under neutral or mild
acidic conditions due to the imine hydrolysis. The group28, 29
also fabricated gemini surfactant and the surfactant with one
head and two hydrophobic tails by bis-aldehyde and alkyl
amines, and the surfactants separately form worm-like
micelles and vesicles and display responsive behaviors to the
because of its utility in protein purification,3,4 water
treatment,5 drug encapsulation6,7 and cosmetic formulation.8
Separation and extraction via coacervation as a well-known
approach, have been utilized for long years, because it has an
array of superior properties, for instance, non-volatility and
non-flammability, high preconcentration factors, and tunability
of coacervate polarity for enriching both organic and inorganic
compounds.9-11 Many studies have reported the application of
nonionic surfactant coacervation as a function of temperature
in the extraction of hydrophobic organic compounds, i.e. cloud
point extraction technique, and the main driving force of
phase separation is hydrophobic interaction.12-14 Recent years,
ionic surfactant-mediated coacervation, enlarges the scope of
coacervation in extraction applications15-17 because of its more
binding sites. In order to realize the release of extracted
compounds
from
coacervation,
stimulus-responsive
coacervation is desired. Applying dynamic covalent
surfactants18 to construct coacervation is here expected to be
one of the most effective approaches to extract and release
a.CAS Key Laboratory of Colloid, Interface and Chemical Thermodynamics, CAS
Research/Education Center for Excellence in Molecular Sciences, Institute of
Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China.
b.University of Chinese Academy of Sciences, Beijing 100049, P. R. China.
*E-mail: yilinwang@iccas.ac.cn
imine bonds between
a non-aggregated state and an
aggregated state. Zhang group30, 31 employed pH-responsive
imine bond to form bola-shaped and H-shaped surfactants
Electronic Supplementary
DOI: 10.1039/x0xx00000x
Information
(ESI)
available:
See
This journal is © The Royal Society of Chemistry 2018
Soft Matter, 2018, 00, 1-7 | 1
Please do not adjust margins

Please do not adjust margins
Soft Matter
Page 2 of 8
View Article Online
DOI: 10.1039/C8SM00773J
Paper
Soft Matter
with both amino and benzyl aldehyde moieties. Compared Synthesis of 4-Formyl-N, N, N-trimethylbenzenaminium Iodide
with the surface-active building blocks, both the surfactants (FBA)
display stronger self-assembling ability, depending on critical
Compound FBA was synthesized according to Figure S1 and
characterized by 1H NMR, 13C NMR, mass spectra, and
hydrolysis pH values. In addition, this kind of pH-responsive
dynamic imine surfactants was also exploited in building
34
elemental analysis. Compound 4-dimethylamino benzaldehyde
stimuli-responsive emulsion,32 supramolecular gel,33,
and
(4.47 g, 30.0 mmol) and iodomethane (9.34 mL, 150.0 mmol)
were dissolved in 40 mL acetone. After being stirred and
refluxed at 70 °C for 8 hours, the mixture was filtered to obtain
the yellow precipitates. Crystallization from methanol gave
selective sensors.35 However, so far coacervation based on
dynamic covalent surfactants has not yet been reported.
Herein we report a pH-responsive coacervation system
formed by 10% hydrolyzed polyacrylamide (PAM) and cationic
ammonium dynamic covalent surfactants (C7-FBA, C8-FBA) to
realize the extraction and release of anionic dye Conge Red (CR)
(Scheme 1). The dynamic covalent surfactants (DS) are formed
by connecting 4-formyl-N, N, N-trimethylbenzenaminium
iodide (FBA) with heptylamine (C7A) or octylamine (C8A)
through a dynamic imine bond. In alkaline conditions, both C7-
FBA and C8-FBA can self-assemble into small micelles. When
PAM is added, coacervation takes place in the mixture due to
the balance of hydrophobic, electrostatic, and solvent
interactions. The coacervate phase with net-work structure is
efficient in extracting CR. By changing the pH of the coacervate
to acidic values, the imine bond is hydrolyzed and the
composition in coacervates is transformed to non-aggregated
state, leading to the release of CR.
1
pure FBA as white solid (40% yield). H NMR (400 MHz, D2O,
ppm): δ 3.76 (s, 9H, CH3), 8.12 (d, 2H, CH, J = 9.00 Hz), 8.24 (d,
2H, CH, J = 9.08 Hz), 10.09 (s, 1H, CHO). 13C NMR (D2O, ppm):
57.08, 121.07, 131.82, 136.80, 150.72, 194.34. MS-ESI (m/z, [M
+ H]+): calcd, 164.1; found, 164.2.
Surface Tension Measurements
The surface tension measurements of the dynamic covalent
surfactants at pH 12.2 and the protonated amines at pH 1.5
were conducted using a Pt/Ir plate method on a DCAT21
tensiometer (Dataphysics Co., Germany). The experiments
were carried out at 25.00 ± 0.01 °C and the calibration of the
tensiometer by measuring pure water before each set of
measurements. Each surface tension curve was repeated at
least twice. The critical micellar concentrations (CMC) of the
dynamic covalent surfactants were determined from the
surface tension curves.
Dynamic Light Scattering (DLS)
The size distribution of C7-FBA and C8-FBA aggregates at pH
12.2 was studied by Nano ZS (Malvern Instruments) at a
scattering angle of 173° equipped with a 4 mW He−Ne laser (λ
= 632.8 nm) and a thermostated chamber at 25.0 ± 0.1 °C.
PAM
CR
Scheme 1 Molecular Structures of FBA, Dynamic Covalent
surfactants (C7-FBA and C8-FBA), CR and PAM.
Fluorescence Measurement
The fluorescence spectra of Nile red (NR) in the dynamic
covalent surfactants were obtained at 25.0 ± 0.1 °C by a
Experimental section
Hitachi F-7000 fluorescence spectrophotometer. NR,
a
hydrophobic molecule, was used to probe the polarity of the
microenvironment in the aggregates. The concentration of NR
was kept around 5 μM. The NR probe in the solution was
excited at 565 nm, and the maximum emission wavelength
Materials
4-Dimethylamino
benzaldehyde,
heptylamine
(C7A),
octylamine (C8A), and nile red (NR) were purchased from Acros
company with a purity higher than 99%. Iodomethane was
purchased from Energy Chemical company. Polyacrylamide
(PAM), 10% hydrolyzed, was purchased from Sigma and the
average molecular weight is approximately 200000. The pKa
value of carboxylate groups of PAM is about 4.60. Congo Red
(CR > 98%) was purchased from the TCI company. All organic
solvents used in the experiments were purchased from Beijing
Chemical Works and were dried and distilled before use.
(λmax
)
of dynamic covalent surfactants at different
concentrations was recorded by the fluorescence
spectrophotometer.
Coacervate Phase Extraction and Release
UV-vis absorption measurements were carried out on a
Shimadau UV 2800 spectrometer to study the extraction and
release efficiency of CR by coacervate phase. 2 mL mixed
solution of dynamic covalent surfactant, PAM and CR was
prepared in a centrifuge tube. The aqueous suspension was
stand for 12 h and then centrifuged at 8000 rpm for 7 min to
separate coacervate phase and dilute phase. The
concentration of CR in the dilute phase, i.e., supernatant, was
determined by the UV spectrometer and the amount of CR
Deionized water (18.2 MΩ·cm) from Milli-Q equipment was
used in all experiments. 1H NMR and 13C NMR of FBA were
recorded on a Bruker Avance 400 MHz spectrometer. Mass
spectra (ESI) were measured on a SHIMADZU LCMS-2010
spectrometer and elemental analysis measurement was
recorded on Flash EA1112.
2 | Soft Matter, 2018, 00, 1-7
This journal is © The Royal Society of Chemistry 2018
Please do not adjust margins

Please do not adjust margins
Soft Matter
Page 3 of 8
View Article Online
DOI: 10.1039/C8SM00773J
Soft Matter
Paper
extracted by coacervate phase was calculated from the 10.06 ppm nearly cannot be found anymore, while a new peak
relationship, extraction efficiency (%) = (C0 − Ce)/C0, where C0 is around 8.45 ppm appears, indicating the formation of imine
the initial concentration of dye and Ce is the equilibrium bond in the dynamic covalent surfactant C7-FBA. Then, by
concentration of dye (mM) in the supernatant. After removing adjusting the pH of the solution to acidic condition, the peak of
the dilute phase, the pH value of the coacervate phase was imine bond at 8.45 ppm disappears, and meanwhile the peak
adjusted to 1.5 and CR was released as purple-black of -CHO reappears, demonstrating the hydrolyzation of imine
precipitate. The release amount of CR was calculated by the bond in C7-FBA. In order to further confirm the formation of
initial and final concentrations of CR in the solution. The dynamic covalent surfactants, elemental analysis of C7-FBA, C8-
experiments were performed at 25.0 °C.
FBA, and FBA solids are also performed as shown in Table S1
(Supporting Information). The experimental values are
Turbidity Measurement
consistent with the theoretical values of C, H, and N
compositions. The MS-ESI spectra of 20 mM C7-FBA and 20
mM C8-FBA at pH 12.2 (Figure S2) show the main peaks
belonging to the formed C7-FBA or C8-FBA. All the above
results confirm the formation of the dynamic covalent
surfactants. Obviously the dynamic covalent surfactants can be
formed or dissociated by conveniently controlling the pH-
The turbidity values of the aqueous solutions of dynamic
covalent surfactants and PAM mixtures were measured against
the surfactant concentration or pH at 670 nm using a
Brinkman PC920 probe colorimeter or a Shimadzu UV−vis
spectrophotometer (model UV-2800) thermostatted at 25.0 ±
0.01 °C. All the measured values were corrected by taking the
turbidity of water at pH 12.2 as zero.
responsive imine bond.
10.06
Scanning Electron Microscopy (SEM)
pH 12.2
pH 12.2
pH 1.5
a
The morphology of the coacervate formed by the dynamic
covalent surfactants and 0.50 wt % PAM was imaged with a
field-emission scanning electron microscope (Hitachi S-4800).
The samples were prepared by freezing a small drop of
coacervate on a clean silica wafer with liquid nitrogen so that
the microstructure of the coacervate phase was retained.
Immediately afterward, the frozen sample was lyophilized
under vacuum at about −55 °C. Finally, a 1−2 nm Pt coating
completed the sample preparation.
8.45
b
10.06
+HCl
9.5
c
10.5
10.0
9.0
8.5
ppm
Figure 1 1H NMR spectra of (a) 20 mM FBA, (b) 20 mM C7-FBA
at pH 12.2, and (c) 20 mM C7-FBA at pH 1.5.
Light microscopy
The image of the liquid-liquid phase separation was captured
with 10 μL of the mixed solution of dynamic covalent
surfactants and 0.50 wt % PAM by a light microscope (XSP-
8C(8CA)) with a mounted digital camera.
pH 13
pH 12
pH 11
1H NMR Spectroscopy
1H NMR measurements of the dynamic covalent surfactants
were performed on a Bruker AV400 FT-NMR spectrometer
operating at 25 ± 2 °C. Deuterium oxide (99.9%) was purchased
from CIL (Cambridge Isotope Laboratories) and used to
prepare the stock solutions of the dynamic covalent
surfactants. The center of the HDO signal (4.790 ppm) was
used as the reference in the D2O solutions.
10
8
4
2
0
6ppm
10.5
10.0
9.5
8.5
9.0 ppm
8.0
7.5
7.0
Figure 2 1H NMR spectra of 20 mM C7-FBA at different pH
values.
Figure 2 shows the 1H NMR spectra of 20 mM C7-FBA at
different pH values. The peak around 8.4 ppm and 10.0 ppm
are respectively assigned to the imine proton and aldehyde
proton. As the pH increases
，the peak for aldehyde proton
weakens significantly, while the intensity of imine proton peak
increases, indicating the higher imine bond conversion
efficiency at high pH value. The imine bond conversion can be
roughly estimated by the ratio of A1/(A1 + A0), where A1 and A0
are separately defined as the integral intensity values of the
peaks of the imine proton and aldehyde proton. When pH
increases to 12.2, most of FBA has been converted to C7-FBA
by the formation of the imine bond. Thus, pH 12.2 is chosen in
all the following experiments. The imine conversion of C7-FBA
and C8-FBA as a function of surfactant concentration is also
Results and discussion
Formation of Dynamic Covalent Surfactants
FBA forms dynamic covalent surfactants (C7-FBA and C8-FBA)
with C7A or C8A through a pH-responsive imine bond. The
formation of imine bond was confirmed by 1H NMR. Herein,
C7-FBA is chosen as a representative with the results shown in
Figure 1. Compared with the 1H NMR spectrum of FBA, the
spectrum of the equimolar mixture of FBA and C7A at pH 12.2
is obvious different. The peak of aldehyde group (-CHO) at
This journal is © The Royal Society of Chemistry 2018
Soft Matter, 2018, 00, 1-7 | 3

Please do not adjust margins
Soft Matter
Page 4 of 8
View Article Online
DOI: 10.1039/C8SM00773J
Paper
Soft Matter
1
concentration increases and then remains at 80% beyond
CMC. That is to say, the formation of micelles favours the
stabilization of imine bond, which was also found in other
similar systems.25
measured by H NMR at the pH 12.2 (Figure S3). The curves
display similar increasing slope at low surfactant concentration
and then remain at about 80%, which will be further discussed
in the following text.
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
C -FBA
(a7)
C -FBA
(d8)
80
30 mM C7-FBA
30 mM C8-FBA
25
20
15
10
5
(a)
C7-FBA
C8-FBA
(b)
70
60
50
40
30
0.8 % PAM
0.5 % PAM
0.3 % PAM
0.1 % PAM
0 % PAM
0.8 % PAM
0.5 % PAM
0.3 % PAM
0.1 % PAM
0 % PAM
C1
C2
C3
(b)
C1 C2
C3
(e)
1.0
0.8
0.6
0.4
0.2
1.0
0.8
0.6
0.4
0.2
0
1
10
100
1000
0.01
0.1
1
10
CDS (mM)
Size (d.nm)
664
660
656
652
648
644
640
665
660
655
650
645
640
C7-FBA
C8-FBA
(c)
(d)
pH 1.5
0.5 % PAM
0.5 % PAM
0.0
0.8
0.0
0.8
(f)
(c)
n
0.6
0.4
0.2
0.0
0.6
0.4
0.2
0.0
o
i
n
o
t
n
a
i
o
i
t
pH 12.2
x
t
a
v
e
a
l
t
r
i
p
e
p
i
c
a
o
m
c
1
10
0.0
0.5
1.0
1.5
2.0
2.5
3.0
o
e
c
r
c
p
CDS (mM)
Cycle
C1
C2
C3
C1
C2
C3
Figure 3 (a) Surface tension curves of C7-FBA and C8-FBA solutions
against the total surfactant concentration at pH 12.2. (b) DLS results
of the aggregates of 30 mM C7-FBA and C8-FBA at pH 12.2. (c) λmax
0
10
20
30
40
50
0
10
20
30
40
CDS (mM)
CDS (mM)
z
of Nile red as a function of the C7-FBA or C8-FBA concentration (CDS
)
Figure 4 (a, d) Turbidity for the mixed solutions of C7-FBA or C8-FBA
with PAM of 0.1, 0.3, 0.5 and 0.8 wt % at 25 °C and pH 12.2,
expressed by the absorbance at 670 nm and plotted against the
surfactant concentration (CDS). (b, e) Representative turbidity curves
of C7-FBA and C8-FBA at 0.50 wt % PAM for the determination of
critical concentrations. (c, f) Phase boundaries of C7-FBA or C8-FBA
at pH 12.2. (d) λmax of Nile red in 30 mM C7-FBA aqueous solutions
in response to the pH cycle process at emission wavelength of 565
nm (Black cube and red circle correspond to pH 12.2 and 1.5,
respectively).
Self-assembly of Dynamic Covalent Surfactants
at 25 °C and pH 12.2
.
To investigate the aggregation of the dynamic covalent
surfactants C7-FBA and C8-FBA, surface tension, fluorescence,
and DLS measurements are performed at 25 °C with the results
Because the fluorescence emission spectra of NR are closely
related to the micelle formation, the pH-controlled micelle
formation and dissociation of the dynamic covalent surfactants
C7-FBA and C8-FBA were examined by the NR fluorescence
emission spectra. As shown in Figure 3d, at pH 12.2, 30 mM C7-
FBA exist as micelles, and the NR emissions are observed at
λmax of 643 ± 2 nm. By modulating the pH to 1.5, λmax shifts to
660 ± 2 nm due to the dissociation of micelles and the release
of NR from the hydrophobic environment of micelles. The λmax
transition of NR in the surfactant solution is reversible when
the pH is switched between acidic and alkaline conditions for
more than 3 cycles. Therefore, the micelle formation and
dissociation of C7-FBA and C8-FBA can be effectively controlled
by tuning the pH of the solution.
depicted in Figure 3 a-c
.
The surface tension measurements indicate that neither
benzene aldehyde FBA nor alkyl amine C7A and C8A are surface
active under pH 12.2, but the formed dynamic covalent
surfactants C7-FBA and C8-FBA are very surface active, with the
surface tension at critical micellization concentration (CMC)
close to 30 mN/m (Figure 3a). The turning points at the surface
tension curves show that the CMC values, which is defined as
the concentration of FBA needed for the aggregate formation
when the mixing molar ratio of FBA with C7A or C8A is 1:1, are
12.78 and 5.54 mM for C7-FBA and C8-FBA, respectively. The
DLS result (Figure 3b) confirms that the aggregates formed by
C7-FBA and C8-FBA are small micelles with an average diameter
of ~ 6 nm.
Phase Behavior of Dynamic Covalent Surfactant/PAM
Mixture
The fluorescence emission spectra of NR in the presence of
the dynamic covalent surfactants strongly depend on the
formation of micelles. Taking C8-FBA as an example, the
maximum emission wavelength (λmax) of NR is about 659 nm
when the concentration is below the CMC, and undergoes a
blue shift with the micellization process, indicating that the NR
molecules are solubilized in less-polar microdomain of the
micelles. In addition, the imine conversion of C7-FBA and C8-
FBA measured by 1H NMR at pH 12.2 (Figure S3) indicates that
the imine conversion quickly increases as the surfactant
Previously, we found that the mixture of cationic ammonium
gemini surfactant (12-6-12) and PAM experiences coacervation
over a wide concentration range and the coacervate phase
37
shows great efficiency in concentrating anionic dyes.36,
Herein, the pH-responsive single-chain dynamic covalent
surfactants are used to form complexes and coacervate with
PAM. At pH 12.2, all the carboxylate groups of PAM are
deprotonated and can bind with the cationic headgroups of C7-
FBA and C8-FBA through electrostatic interaction. The phase
4 | Soft Matter, 2018, 00, 1-7
This journal is © The Royal Society of Chemistry 2018
Please do not adjust margins

Please do not adjust margins
Soft Matter
Page 5 of 8
View Article Online
DOI: 10.1039/C8SM00773J
Soft Matter
Paper
should be attributed to the stronger self-assembly abilities and
lower CMC values of C8-FBA.
behavior of C7-FBA and C8-FBA with PAM was monitored by
turbidity measurement as a function of the dynamic covalent
surfactant concentration (CDS) at constant PAM concentration
(CPAM). All the result are shown in Figure 4. The turbidity curves
of C7-FBA/PAM (Figure 4a) and C8-FBA/PAM (Figure 4d) show
similar variation tendency and can be divided into four regions
by three critical surfactant concentrations C1, C2, and C3 (Figure
4b and 4e), and thus the obtained phase boundaries are
derived (Figure 4c and 4f).
C7-FBA
100
80
60
40
20
0
(a)
34
36
38
40
42
44
46
100
80
60
40
20
0
C8-FBA
(b)
22
24
26
28
30
32
CDS (mM)
C7-FBA
C8-FBA
(c)
100
80
60
40
20
0
Figure 5 Coacervate droplets imaged with (a) 30.0 mM C7-FBA and
0.5 wt % PAM, (d) 20.0 mM C8-FBA and 0.5 wt % PAM by light
microscopy at pH 12.2. The SEM image of the coacervate formed by
30.0 mM C7-FBA and 0.5 wt % PAM (b), 40.0 mM C7-FBA and 0.5 wt %
PAM (c), 20.0 mM C8-FBA and 0.5 wt % PAM (e), and 30.0 mM C8-
FBA and 0.5 wt % PAM (f) at pH 12.2.
0.0
0.2
0.4
0.6
0.8
1.0
CCR (mM)
Figure 6 Extraction efficiency of 0.03 mM CR by the dynamic
covalent surfactant/0.5 wt % PAM coacervate plotted against the
concentration of C7-FBA (a) and C8-FBA (b). (c) Extraction efficiency
of CR by the dynamic covalent surfactant/PAM coacervate as a
function of the CR concentration (CCR).
In the following text, the phase behavior will be discussed by
taking the mixture of C7-FBA and PAM as a representative.
Below C1, which is close to the CMC of C7-FBA, the mixed
solution is transparent and the turbidity is close to zero,
indicating that no aggregate is formed in this region. The
increase of turbidity beyond C1 suggests the complexation of
C7-FBA and PAM. Then, the turbidity starts to increase abruptly
at C2 and oil droplets appear under light microscopy (Figure 5a,
d). Upon further addition of C7-FBA, the turbidity continues to
increase and reaches a maximum. The SEM images in Figure 5
show that the coacervate phase exhibits large network
structures. Beyond C3, the dynamic covalent surfactant C7-FBA
starts to precipitate out due to the limitation in solubility. So C2
and C3 are defined as the starting and ending point of
coacervation. The interaction process resembles those
observed in our previous work36, 37: below C1, the surfactant
monomers bind onto the oppositely charged chain of PAM
through electrostatic interaction; beyond C1, the surfactant
micelles start to form complexes with polyelectrolyte as
Extraction and Release Process of CR
On the basis of the above studies, the dynamic covalent
surfactant/PAM cocervate is utilized to extract anionic dye CR
from the aqueous solution. The extraction efficiency of CR by
the dynamic covalent surfactant/PAM coacervate as a function
of the surfactant concentration (CDS) or the CR concentration
(CCR) is shown in Figure 6. Figure 6a and b show that the
extraction efficiency of C7-FBA with 0.5 % PAM or C8-FBA with
0.5 % PAM slightly increases in lower surfactant concentration
region and then reaches the maximum close to 98% due to the
increase of the coacervate amount. Further increasing the
surfactant concentration, the extraction efficiency decreases
owing to the partially dissolution of the coacervate phase. All
the extraction efficiency values are higher than 80% in the
indicated by the increase of turbidity; the association of the investigated concentration regions, implying that the
surfactant/polyelectrolyte complexes lead to coacervation
between C2 and C3; and the region beyond C3 is the
precipitation region. According to the phase boundaries
(Figure 4c and 4f), by increasing the PAM concentration, all the
critical concentrations C1, C2, and C3 shift to larger values and
the coacervation range expands greatly. Compared to C7-FBA,
C8-FBA is more easily to form coacervates and the
coacervation covers a larger concentration range, which
coacervate phase shows great efficiency in extracting CR from
water. Then, 40 mM C7-FBA with 0.5 % PAM and 25 mM C8-
FBA with 0.5 % PAM are chosen to study the extraction
efficiency to CR of different concentrations (Figure 6c). In the
CR concentration range from 0.1 to 1.0 mM, the extraction
efficiency keeps at 98%. The preconcentration of CR by the
coacervate phase from aqueous phase should be mainly driven
by the electrostatic interaction between CR and the cationic
This journal is © The Royal Society of Chemistry 2018
Soft Matter, 2018, 00, 1-7 | 5

Please do not adjust margins
Soft Matter
Page 6 of 8
View Article Online
DOI: 10.1039/C8SM00773J
Paper
Soft Matter
head groups of dynamic covalent surfactants, the π−π stacking
between the benzene rings, and the hydrophobic interaction
between the benzene ring and the hydrophobic tails of
surfactant.
Subsequently, the extraction and release process of CR by
the coacervate of 0.5 % PAM with 40.0 mM C7-FBA or 25.0 mM
C8-FBA is investigated by changing pH. Figure 7a shows the
typical experiment process by taking C7-FBA and PAM as a
representative. The concentrated CR solution is added into 10
mL C7-FBA/PAM coacervate solution and the mixture is
blended. Then, the coacervate phase coalesces into the
bottom with the dye molecules extracted in it. After the
supernatant phase is removed, the pH value of the coacervate
phase is tuned to 1.5 by adding HCl. After centrifugation, CR
precipitates out as purple-black solid. The turbidity curves of
the dynamic covalent surfactant/PAM mixed solutions in
Figure 7b show that decreasing the pH from 12.2 to 1.5 makes
the cloud coacervate change into a homogeneous and clear
solution, and thus the dye is released. In the above steps, the
supernatant phases are used to determine the respective CR
concentration by UV-vis absorption spectroscopy. The
extraction and release efficiency of CR are calculated by the
difference of the initial and final concentration of CR in the
solution, indicating with the extraction and release efficiency
values are all above 98% for either C7-FBA/PAM or C8-
FBA/PAM (Figure 7c). Thus, the CR can be effectively extracted
and released by simply switching the pH of the coacervate.
Figure 8 Possible mechanism of the extraction and release of
CR in dynamic covalent surfactant/PAM mixture.
A possible mechanism of the pH-triggered extraction and
release process is summarized in Figure 8. At pH 12.2, C7-FBA
or C8-FBA forms coacervate with PAM in a wide concentration
region. The coacervate phase with a net-work structure can
efficiently solubilize anionic dye CR through electrostatic
interaction, hydrophobic interaction and π-π interaction, while
the supernatant phase contains less surfactant, PAM and CR
molecules. Through this step, the dye is enriched in the
coacervate phase. Then, the upper phase is removed for the
subsequent release step. By decreasing the pH of coacervate
from 12.2 to 1.5, C7-FBA and C8-FBA are dissociated into non-
amphiphilic FBA and protonated amines due to the hydrolysis
of imine bond in the surfactants, resulting that CR separates
out as purple-black solid with the protonation of sulfonic
groups in CR. The surface tension curves of C7A and C8A at pH
1.5 show that the surface tension is still decreasing at the
experimental concentrations without the appearance of
critical points, demonstrating the protonated amines exist as
monomers (Figure S4). Without the complexation and
association between PAM and micelles, the systems cannot
form coacervate at acidic conditions. Owing to the fact that
FBA, protonated amines, and PAM are all hydrophilic, the
mixed solutions are homogeneous and clear, and can be
recycled. Therefore, the recovery and reuse of dynamic
covalent surfactants, polyelectrolytes, and dyes are realized by
tuning the pH.
Conclusions
In this work, dynamic covalent surfactants have been
constructed via the formation of imine bonds between
aldehyde moiety and amines. The mixtures of aldehyde FBA
with amines C7A and C8A form cationic single-chain surfactants
(C7-FBA and C8-FBA) at alkaline condition and self-aggregate
into micelles, but the surfactants and the micelles are
dissociated at acidic condition due to the break of imine bonds
in the dynamic covalent surfactants. At alkaline condition, the
dynamic covalent surfactant/PAM mixtures in aqueous
solution undergo several phase states as the surfactant
concentration increases, including surfactant monomer-PAM
complexes, micelle-PAM complexes, coacervate and
precipitate. The area of coacervate region increases with the
increase of the PAM concentration. The net-work structure of
the coacervate phase promotes the preconcentration of
Figure 7. (a) Photos of extraction and release of CR by the
coacervate formed with C7-FBA and PAM at pH 12.2, and the
subsequent release process by changing the pH to 1.5. (b)
Turbidity curves of the mixed solution of 40.0 mM C7-FBA with
0.5 wt % PAM or 25.0 mM C8-FBA with 0.5 wt % PAM as a
function of pH at 25.0 °C. (c) Extraction and efficiency of 0.03
mM CR by the coacervate of 40.0 mM C7-FBA with 0.5 wt %
PAM or 25.0 mM C8-FBA with 0.5 wt % PAM by changing pH
(extraction at pH 12.2; release at pH 1.5).
6 | Soft Matter, 2018, 00, 1-7
This journal is © The Royal Society of Chemistry 2018
Please do not adjust margins

Please do not adjust margins
Soft Matter
Page 7 of 8
View Article Online
DOI: 10.1039/C8SM00773J
Soft Matter
Paper
anionic dye CR through electrostatic interaction, hydrophobic 14 P. Taechangam, J. F. Scamehorn, S. Osuwan and T.
interaction and π-π interaction. The extraction efficiency keeps Rirksomboon, Colloids Surf., A, 2009, 347, 200-209.
at 98% in the CR concentration range from 0.1 to 1.0 mM, 15 P. Weschayanwiwat, O. Kunanupap and J. F. Scamehorn,
which is much smaller than dye concentrations in normal Chemosphere, 2008, 72, 1043-1048.
wastewater of dyes. By changing the pH into acidic condition, 16 D. Chen, P. Zhang, Y. Li, Z. Mei and Y. Xiao, Anal. Bioanal.
the coacervate transits into a homogeneous and clear solution, Chem., 2014, 406, 6051-6060.
while CR precipitates out as purple-black solid with the 17 N. Pourreza and M. Zareian, J. Hazard. Mater., 2009, 165
protonation of sulfonic groups. So the efficient extraction and 1124-1127.
release of the dye molecules are realized by tuning the pH. In 18 D. A. Fulton, In Supramolecular Amphiphiles, The Royal
this way, dyes as well as FBA, amine, and PAM can be recycled Society of Chemistry, 2017
and reused. The results provide a novel and convenient route 19 P. T. Corbett, J. Leclaire, L. Vial, K. R. West, J. -L. Wietor, J. K.
to fabricate functional dynamic covalent surfactants through M. Sanders and S. Otto, Chem. Rev., 2006, 106, 3652-3711.
,
.
dynamic covalent bonds, and set up a potential and efficient 20 A. Herrmann, Chem. Soc. Rev., 2014, 43, 1899-1933.
method to enrich and recycle dyes in wastewater through pH- 21 A. Wilson, G. Gasparini and S. Matile, Chem. Soc. Rev., 2014,
triggered coacervation of dynamic covalent surfactants and
polymer.
43, 1948-1962.
22 X. Su and I. Aprahamian, Chem. Soc. Rev., 2014, 43, 1963-
1981.
23 Y. Jin, C. Yu, R. J. Denman and W. Zhang, Chem. Soc. Rev.,
2013, 42, 6634-6654.
Conflicts of interest
24 S. J. Rowan, S. J. Cantrill, G. R. L. Cousins, J. K. M. Sanders and
J. F. Stoddart, Angew. Chem., Int. Ed., 2002, 41, 898-952.
25 R. Nguyen, E. Buhler and N. Giuseppone, Macromolecules,
2009, 42, 5913-5915.
There are no conflicts to declare.
Acknowledgements
26 R. Nguyen, L. Allouche, E. Buhler and N. Giuseppone, Angew.
Chem., Int. Ed., 2009, 48, 1093-1096.
This work was supported by National Natural Science
Foundation of China (21633002) and Beijing National
Laboratory for Molecular Sciences (BNLMS).
27 C. B. Minkenberg, L. Florusse, R. Eelkema, G. J. M. Koper and
J. H. van Esch, J. Am. Chem. Soc., 2009, 131, 11274-11275.
28 C. B. Minkenberg, F. Li, P. van Rijn, L. Florusse, J. Boekhoven,
M. C. A. Stuart, G. J. M. Koper, R. Eelkema and J. H. van Esch,
Angew. Chem., Int. Ed., 2011, 50, 3421-3424.
References
1
2
M. Wang and Y. L. Wang, Soft Matter, 2014, 10, 7909-7919.
W. Zhao and Y. L. Wang, Adv. Colloid Interface Sci., 2017, 239
199-212.
29 C. B. Minkenberg, B. Homan, J. Boekhoven, B. Norder, G. J.
,
M. Koper, R. Eelkema and J. H. van Esch, Langmuir, 2012, 28
,
13570-13576.
3
4
P. L. Dubin, J. Gao and K. Mattison, Sep. Purif. Rev., 1994, 23,
30 G. Wang, C. Wang, Z. Wang and X. Zhang, Langmuir, 2011,
27, 12375-12380.
1-16.
M. B. Linder, M. Qiao, F. Laumen, K. Selber, T. Hyytiä, T.
31 G. Wang, C. Wang, Z. Wang and X. Zhang, Langmuir, 2012,
28, 14567-14572.
Nakari-Setälä and M. E. Penttilä, Biochemistry, 2004, 43
,
11873-11882.
32 G. Ren, L. Wang, Q. Chen, Z. Xu, J. Xu and D. Sun, Langmuir,
2017, 33, 3040-3046.
5
6
Y. L. Wang, J. Banziger, P. L. Dubin, G. Filippelli and N. Nuraje,
Environ. Sci. Technol., 2001, 35, 2608-2611.
33 Y. Wang, P. Xing, S. Li, M. Ma, M. Yang, Y. Zhang, B. Wang
and A. Hao, Langmuir, 2016, 32, 10705-10711.
34 C. B. Minkenberg, W. E. Hendriksen, F. Li, E. Mendes, R.
Eelkema and J. H. van Esch, Chem. Commun., 2012, 48, 9837-
9839.
S. S. Jyothi, A. Seethadevi, K. S. Prabha, P. Muthuprasanna
and P. Pavitra, Int. J. Pharm. Bio. Sci., 2012, 3, 509-531.
7
8
D. J. Burgess and J. E. Carless, Int. J. Pharm., 1985, 27, 61-70.
T. H. Kalantar, C. J. Tucker, A. S. Zalusky, T. A. Boomgaard, B.
E. Wilson, M. Ladika, S. L. Jordan, W. K. Li, X. Zhang and C. G.
Goh, J. Cosmet. Sci., 2007, 58, 375-383.
35 X. Wu, X.-X. Chen, M. Zhang, Z. Li, P. A. Gale and Y.-B. Jiang,
Chem. Commun., 2016, 52, 6981-6984.
9
A. Ballesteros-Gómez, M. D. Sicilia and S. Rubio, Anal. Chim.
Acta, 2010, 677, 108-130.
36 M. Deng, M. Cao and Y. L. Wang, J. Phys. Chem. B, 2009, 113
,
9436-9440.
10 W. L. Hinze and E. Pramauro, Crit. Rev. Anal. Chem., 1993,
24, 133-177.
37 W. Zhao, Y. Fan, H. Wang and Y. L. Wang, Langmuir, 2017,
33, 6846-6856.
11 A. Melnyk, L. Wolska and J. Namieśnik, J. Chromatogr. A,
2014, 1339, 1-12.
12 E. Tatara, K. Materna, A. Schaadt, H.-J. Bart and J.
Szymanowski, Environ. Sci. Technol., 2005, 39, 3110-3115.
13 N. Pourreza, S. Rastegarzadeh and A. Larki, Talanta, 2008,
77, 733-736.
This journal is © The Royal Society of Chemistry 2018
Soft Matter, 2018, 00, 1-7 | 7

Soft Matter
Page 8 of 8
View Article Online
DOI: 10.1039/C8SM00773J
Table of Contents Graphic
Coacervation of Dynamic Covalent Surfactant with Polyacrylamide: Property
and Application
Weiwei Zhao,†,‡ Hua Wang,†,‡ and Yilin Wang*,†,‡
†Key Laboratory of Colloid, Interface and Chemical Thermodynamics, CAS Research/Education Center
for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing
100190, P. R. China
‡University of Chinese Academy of Sciences, Beijing 100049, P. R. China
Coacervation of cationic dynamic covalent surfactant with polyacrylamide and its application in
extracting and releasing anionic dye in water.
1