CO2-responsive aliphatic tertiary amine-modified alginate and its application as a switchable surfactant

Article abstract of DOI:10.1016/j.carbpol.2016.07.079

A new kind of hexyl diethyl tertiary amine-grafted amphiphilic alginate derivative (HDEA-Alg) was synthesized from (6-bromo-hexyl)-diethyl-amine (BHDEA) and sodium alginate (NaAlg) through esterification. The structure of HDEA-Alg was confirmed by FT-IR and NMR spectroscopies. The grafting ratio was calculated according elemental analysis and thermodynamic property was analyzed by TG. The CO₂/N₂-responsive performance of HDEA-Alg in aqueous solution was demonstrated by surface tension and conductivity measurements. Stable emulsions of liquid paraffin were easily prepared in the presence of the HDEA-Alg. These emulsions can be de-emulsified by bubbling CO₂ through the emulsions at 5?°C for 30?min, resulting in complete oil/water phase separations. They can be re-emulsified by bubbling N₂ through the solutions at 50?°C for 30?min with the aid of homogenization.

Full text of DOI:10.1016/j.carbpol.2016.07.079

Carbohydrate Polymers 153 (2016) 1–6
Contents lists available at ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
CO -responsive aliphatic tertiary amine-modified alginate and its
2
application as a switchable surfactant
∗
Jisheng Yang , Hongbiao Dong
School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 May 2016
Received in revised form 18 July 2016
Accepted 19 July 2016
Available online 20 July 2016
A new kind of hexyl diethyl tertiary amine-grafted amphiphilic alginate derivative (HDEA-Alg) was
synthesized from (6-bromo-hexyl)-diethyl-amine (BHDEA) and sodium alginate (NaAlg) through ester-
ification. The structure of HDEA-Alg was confirmed by FT-IR and NMR spectroscopies. The grafting ratio
was calculated according elemental analysis and thermodynamic property was analyzed by TG. The
CO2/N2-responsive performance of HDEA-Alg in aqueous solution was demonstrated by surface tension
and conductivity measurements. Stable emulsions of liquid paraffin were easily prepared in the presence
Keywords:
◦
of the HDEA-Alg. These emulsions can be de-emulsified by bubbling CO2 through the emulsions at 5 C
Switchable surfactant
Modified alginate
CO2-responsive
for 30 min, resulting in complete oil/water phase separations. They can be re-emulsified by bubbling N2
◦
through the solutions at 50 C for 30 min with the aid of homogenization.
©
2016 Elsevier Ltd. All rights reserved.
1
. Introduction
Magnetic-field intensity trigger is limited to the small application
range. And the addition of oxidants or reductants may cause prod-
uct contamination. More recently, switchable systems that use CO2
as the trigger have got increasing attention due to their advantages
In the past decade, switchable surfactants have attracted rapidly
growing interest (Jiang, Zhu, Cui, & Binks, 2013) due to their
tremendous potential in many industrial applications, such as
cleaning, fuel production, oil recovery, oil transport, and emulsion
polymerization. By using these surfactants, the emulsions or foam
can be stabilized only temporarily and have to be demulsified or
defoam at a specific desired stage.
Switchable surfactants are compounds possessing tunable sur-
face activity in response to changes in environmental condition.
Common stimuli are pH (Liu, Wang, Zou, Wei, & Tong, 2012), tem-
perature (Hu, Ge, Han, & Guo, 2015; Jochumab & Theato, 2013;
Zoppe, Venditti, & Rojas, 2012), light (Jochumab and Theato, 2013;
Mirarefi & Ted Lee, 2010), magnetic-field (Czaun, Hevesi, Takafuji,
(Pocoví-Martínez et al., 2013). Carbon dioxide (CO ) is nontoxic,
2
inexpensive, abundant, and an environmentally friendly chemical
reagent. And the facile addition of CO allows for a large-scale oper-
2
ation (Liu, Lu, Wang, Li, & Zhu, 2014). Most importantly, it can be
readily removed by N2 or air, which is as well abundant and envi-
ronmentally friendly. Accordingly, CO /N –responsive surfactants
2
2
are useful for green chemical processes such as extraction of organic
solvents without distillation (Jessop et al., 2010) and destabiliza-
tion of colloidal polymer latexes without adding chemicals (Fowler
et al., 2011).
Jessop and co-workers have reported a type of CO -triggered
2
&
(
2
Ihara, 2008; Melle, Lask, & Fuller, 2005), oxidants/reductants
Cheng, Ren, Gao, Liu, & Tong, 2007; Ghosh, Irvin, & Thayumanavan,
007). However, it is worth noting that each type of stimuli has its
switchable cationic surfactant containing an amidine group (Liu,
Jessop, Cunningham, Eckert, & Liotta, 2006). Acetamidines with a
long hydrophobic chain form bicarbonate salts in the presence of
CO2 and water (Jessop, Mercera, & Heldebrant, 2012). These salts
are surfactants that stabilize emulsions and could be recovered
when bubbling an inert gas like N2 or Ar through the solution to
downside (Qian, Zhang, Qiu, & Zhu, 2014). For example, repeated
switchable cycles of pH-responsive surfactants require repeated
addition of acids and bases to the solution, which may contaminate
the system and weaken the switchability due to salt accumula-
tion. Changing the temperature for a large volume sample is also
slow and energy consuming. Light is limited to its radiation depth.
expel CO . However, the amidine group has some drawbacks that
2
might limit its utilization in various applications (Lin & Theato,
2013). The synthesis of amidine-containing monomers or com-
pounds is complex and very challenging. And the costs of amidine
groups cannot be neglected. These disadvantages have motivated
to investigate amine group instead of amidine group in the prepa-
∗ Corresponding author.
ration of CO -responsive polymers. As tertiary amines head groups
2
E-mail address: jsyang@yzu.edu.cn (J. Yang).
http://dx.doi.org/10.1016/j.carbpol.2016.07.079
0
144-8617/© 2016 Elsevier Ltd. All rights reserved.

2
J. Yang, H. Dong / Carbohydrate Polymers 153 (2016) 1–6
have lower basicity and switch off far more quickly than the
amidines, in recent years, a lot of studies have been reported on
poly (N,N-(dimethylamino)ethyl methacrylate) (PDMAEMA) which
containing tertiary amine groups (Han, Tong, Boissie r` e, & Zhao,
All tests were carried out according to previous reports (Yang, Zhou,
& He, 2013).
2.4. Assessing surfactant switchability
2
012; Xu et al., 2013; Zhang, Yu, Wang, Li, & Zhu, 2012). Zhang and
co-workers report the synthesis of PDMAEMA-b-PMMA diblock
copolymer (PDM) (Zhang et al., 2012). Such a polymeric surfac-
tant was prepared by block copolymerization of DMAEMA with a
hydrophobic comonomer. The hydrophobic block provides root-
ing to latex particles, the hydrophilicity of PDMAEMA block could
be switched by treating with CO . We hypothesized that CO -
responsive polymeric surfactants could also be prepared by grafting
aliphatic tertiary amine onto a hydrophilic alginate. The hydropho-
bicity of aliphatic tertiary amine could be switched by bubbling
The reversibility of the conversion from active to inactive form
◦
was demonstrated by bubbling CO2 (at 5 C for 30 min) followed by
◦
N2 (at 50 C for 30 min) through solutions of HDEA-Alg and measur-
ing the change in surface tension and conductivity of the solution.
The surface tensions and conductivity of NaAlg and HDEA-Alg aque-
ous solution were measured by a surface tension meter (DCAT11)
2
2
◦
with a platinum plate and a conductivity meter (DDS-11A) at 20 C,
respectively.
CO2 or N . In this paper, we report the synthesis of (6-bromo-
2.5. Emulsions preparation and demulsification
2
hexyl)-diethyl-amine (BHDEA) grafted sodium alginate derivatives
(
HDEA-Alg) through esterification and using tetrabutyl ammo-
Emulsions were prepared by improving method on literature
(Ge, Shao, Lu, & Guo, 2014). Oil in water emulsions were prepared by
first mixing the liquid paraffin into the aqueous phase (containing
various concentrations of HDEA-Alg) using a superfine homoge-
nizer FA25 (Fluko Equipment Shanghai Co.) at 10,000 rpm for 3 min,
followed by an ultrasonic processor VCX 750 (Sonics & Materials
Inc.) with the energy output of the probe setting to 300 W for 3 min.
To verify the switchable performance of the emulsions, CO2 was
nium bromide (TBAB) as phase transfer catalyst. The product was
characterized by FT-IR and 1H NMR spectroscopies. The surface
tension and conductivity of HDEA-Alg in aqueous solution were
investigated to assess surfactant switchability. We also demon-
strated the applicability of the product as surfactants for the
preparation of emulsions and tested the CO /N -triggered emul-
2
2
sification/demulsification of the emulsion system.
◦
bubbled into the emulsions at 5 C for 30 min and switched back by
◦
bubbling N2 through the solution at 50 C for 30 min, followed by
2
. Materials and methods
re-homogenization for 3 min.
2.1. Materials
2.6. Fluorescence microscopy
¯
Sodium alginate (NaAlg, M␩∼ 430 kDa, M/G = 0.18), diethyl ether
Images of the emulsion microstructure were acquired using
(
(
purity ≥99%), Diethylamine (DEA, 99%), N,N-dimethylformamide
purity ≥99%), and paraffin liquid (purity ≥98.5%) were purchased
an inversion fluorescence microscope (IX83, Olympus). Approxi-
mately 10 ml of emulsion was placed in a test tube, and moderate
rhodamine 6G aqueous solution (1 mg/ml) was added and mixed
for 30 min. The mixture was then dropped on a microscope slide
and covered with a coverslip before observed.
from Sinopharm Chemical Reagent Co. 1,6-Dibromohexane (purity
≥
98%) was provided by Energy Chemical. Tetrabutylammonium
bromide (TBAB, 99%) was purchased from Aladdin. Unless specially
stated, all materials were guaranteed analytical reagents and used
as received without further purification.
3
. Results and discussion
3.1. Characterization of HDEA-Alg
2.2. Synthesis and purification of BHDEA
NaAlg was modified by use of the phase transfer catalysis TBAB
According to the literature (Albrecht, Ehrler, & Mühlebach,
003), (6-bromo-hexyl)-diethyl-amine (BHDEA) was prepared by
to form ester linkages between BHDEA molecules and the car-
boxylate groups on the alginate polymer backbone. The synthesis
principle of HDEA-Alg is shown in Scheme 1.
The structures of samples were confirmed by FT-IR as shown in
Fig. 1. From the spectrum of NaAlg (Fig. 1a), it is being observed
2
reacting 1,6-dibromohexane (61 g, 0.25 mol) with diethylamine
◦
(
7.8 ml, 75 mmol) in diethyl ether (150 ml) at 25 C refluxed
for 5 days. The reaction mixture was poured into aqueous HCl
0.2 M, 150 ml). The aqueous layer was washed with diethyl ether
(
(
−
1
that a broad peak at 3450 cm
tions of O H, and a small peak at 2929 cm is attributed to the
H stretching vibrations of methyne groups. The bands at 1096
is due to the stretching vibra-
2 × 100 ml) and neutralized with NaOH to pH 12. After extraction
−1
with diethyl ether (3 × 100 ml), the organic layers were dried over
C
MgSO and evaporated to leave BHDEA as a yellow oil.
4
−
1
and 1028 cm are assigned to C
the saccharide structure. It is further noted that two strong peaks
at 1612 and 1417 cm are assigned to asymmetric and symmet-
ric stretching vibrations of carboxylate groups. Comparing that of
NaAlg, the spectrum of HDEA-Alg (Fig. 1b) contains the characteris-
tic hydroxyl and carboxyl bands, but also features additional peaks.
O
−C stretching vibrations of
−
1
2
.3. Synthesis and characterization of HDEA-Alg
As described by Scheme 1, NaAlg (2.0 g) and BHDEA (5.0 g)
were added in 60 ml of acetone/water (5/1,v/v) containing TBAB
◦
−1
(
2 mmol) by stirring at 60 C for 30 h. The reaction mixture was fil-
A broad peak appears in HDEA-Alg from 2960 to 2860 cm due to
tered and washed with absolute ethanol (2 × 100 ml). The crude
product was dissolved into water and then poured into the dialysis
bag. The solution was dialyzed against the distilled water for 3 days
and lyophilized to get the pure HDEA-Alg. The chemical structure
of product was characterized by Fourier transform infrared spec-
the peak overlap of methy, methylene and methyne groups, and the
−
1
peaks of 1731 and 1250 cm are attributed to the C O and C
O
component of an ester bond respectively. Vibrations of C N is mea-
−
1
sured to be 1078 cm in BHDEA, which overlaps with the peaks
−
1
of C
O C stretching vibrations around 1096 and 1028 cm . The
1
troscopy (FT-IR, Tensor 27, Bruker), NMR spectroscopy ( H NMR,
appearance of the peaks suggests that BHDEA successfully grafted
onto alginate.
1
3
AVANCE 600, Bruker; C AVANCEIII400, Bruker) and thermogravi-
metric analysis (TG, STA409PC). The grafting ratio (Nalkyl/Nhexuronic
of HDEA-Alg was determined by elemental analysis (Vario EL cube).
)
1H NMR was investigated to further confirm the chemical struc-
ture of the graft polymer. The 1H NMR spectrum of NaAlg and

J. Yang, H. Dong / Carbohydrate Polymers 153 (2016) 1–6
3
HO
HO
HO
NaOOC OH
O
NaOOC
NaOOC
O
O
OH
O
O
OH
O
O
O
O
O
HO
O
O
NaOOC OH
O
C
HO
O
C
HO
OH
n
OH
n
O
O
NaAlg
TBAB
2 2
CO , H O
+
N
2
, Heat
Br
N
N
NH HCO
3
BHDEA
HDEA-Alg
Scheme 1. The synthesis principle of HDEA-Alg and its CO2/N2 responsibility.
Fig. 1. FT-IR spectra of NaAlg (a) and HDEA-Alg (b).
HDEA-Alg are shown in Fig. 2a. The proton peaks from 3.6 to
5
.1 ppm contributed to the H of alginate, in which the anomeric
protons are observed in the region 4.5–5.1 ppm. In contrast with
the spectrum of NaAlg, additional peaks in spectrum of HDEA-
Alg are observed from 1.0 to 3.5 ppm, which were assigned to the
methyl and methylene protons of aliphatic tertiary amine respec-
tively. Affected by N and O atoms, the chemical shift of methyl
13
protons and methylene protons both increased. The solid-state
C
NMR spectra of NaAlg and HDEA-Alg samples are shown in Fig. 2b.
Comparing to NaAlg, a series of peaks appear in HDEA-Alg from
1
0 to 65 ppm because of the introducing of alkyl tertiary amine
1
3
chain. The C NMR spectra of HDEA-Alg exhibits peaks at 10 ppm
methyl groups), and two peaks at 20 ppm and 28 ppm assigned
(
to methylene groups. Meanwhile, the peaks of 48 ppm and 55 ppm
are attributed to C N and C O groups. On the basis of the above
data, it could be concluded that HDEA-Alg was synthesized.
The grafting ratio (X) of the HDEA-Alg is 12.8% calculated by
the following formula, according to percentage content of N in the
HDEA-Alg measured by an elemental analyzer.
Fig. 2. 1H NMR (a) and 13C NMR (b) spectra of NaAlg and HDEA-Alg.
CO2 and neighboring hydroxyl dehydration. The weightlessness of
HDEA-Alg in the second stage is obviously higher than the NaAlg
because of the thermal scission of the ester and the evolution of ter-
tiary amine molecules. This finding further supports the presence
of ester bond formatting between DEHA and NaAlg.
M · X
3
N% =
M · X + M (1 − X)
1
2
3
.2. CO /N -responsive performance of HDEA-Alg in aqueous
2 2
N% · M
2
X(%) =
solution
M − N% · M + N% · M
3
1
2
(
M represents the sum of the atomic weight of C16H29O N; M rep-
Fig. 4a displays the plots of surface tension versus different con-
centration of NaAlg and HDEA-Alg. Attributing to the introduction
of hydrophobic chain by esterification, the synthesized surfactant
has lower surface tension than NaAlg in aqueous solution under the
same concentration. To assess surfactant switchability, the surface
tension of HDEA-Alg (0.4 wt%, the critical micelle concentration)
aqueous solutions were observed when CO2 followed by N2 were
1
6
2
resents the sum of the atomic weight of C H7O Na; M represents
the relative atomic mass of N).
Fig. 3 shows the TG analysis curves of NaAlg and HDEA-Alg. As
we know, the first stage region belongs to the loss of combined
water of NaAlg in the 30–200 C, and in the second stage from 220
6
6
3
◦
◦
to 280 C, the weight loss of NaAlg should be the carboxyl take off

4
J. Yang, H. Dong / Carbohydrate Polymers 153 (2016) 1–6
3
.3. CO /N -responsive performance of emulsions stabilized by
2 2
HDEA-Alg
The HDEA-Alg was employed as surfactants with different con-
centrations in water for the preparation of emulsions. Paraffin
liquid was used as the oil phase. And the emulsifying performance
was found to increase with increasing concentration of HDEA-
Alg from 0.4 to 1.0 wt% as shown in Fig. 6a–d. A stable emulsion
could be prepared until the concentration of HDEA-Alg reaches
about 1.0 wt%. To verify the switchable performance of the emul-
◦
sions, emulsion d was bubbled with CO2 at 5 C for 30 min and
◦
switched back by bubbling N2 through the solution at 50 C. Both
were observed after 24 h. On one hand, HDEA-Alg in emulsions
lost their surface activity by bubbling CO2 and returned to the
water phase and no stable emulsion could be formed after re-
homogenization (Fig. 6e). On the other hand, once N2 was bubbled
◦
through the mixture at 50 C for 30 min, the stability of the emul-
sions was reestablished after re-homogenization (Fig. 6f). Moderate
rhodamine 6 G aqueous solution (1 mg/ml) was added and mixed
for 30 min to observe emulsion d and emulsion e. Fig. 6g shows
the fluorescence microscopy images of O/W emulsion d, we could
clearly observe a yellow ring encompassing a dark spot. Because of
opposite charges attracted, the fluorescent dye of Rh6G with posi-
tive charges bound to the HDEA-Alg with the negative charges, so
that the region of macromolecules appeared yellow under ultra-
violet light. Oil droplets, however, appeared nonfluoresced black
spherical area because there was no interaction between Rh6G and
the molecules of oily phase. The bright layer outside oil droplet
showed that the macromolecular membrane formed due to the
HDEA-Alg molecular adsorption at the oil/water interface. But in
fluorescence microscopy images of O/W emulsion e (Fig. 6h), a
large area appeared yellow and oil droplets were coalesced sig-
nificantly. We know that HDEA-Alg with bicarbonate is a kind of
water-soluble macromolecules, so distributes homogeneously in
continuous phase of the emulsion.
Fig. 3. TG curves of samples.
bubbled through the solution, just as shown in Fig. 4b. CO2 was
bubbled through the solution for 30 min at 5 C and the surface
tension of the solution was measured to be 58.7 mN/m at 20 C,
which implies that the tertiary amine switchable surfactant has
been converted to bicarbonate and lead to enhanced hydrophilic-
◦
◦
ity. Following this procedure, N was bubbled through the solution
2
◦
for 30 min at 50 C and surface tension of the solution decreased to
6.6 mN/m. After another two cycles of bubbling CO /N , there is
no discernible loss in performance.
The conductivity of NaAlg and HDEA-Alg aqueous solutions of
different concentration was also measured as shown in Fig. 5a.
The conductivity all increase with the increase of concentration.
It is worth noting that the HDEA-Alg aqueous solutions have lower
conductivity than NaAlg aqueous solutions when the concentra-
tion is same, indicating that Na+ of NaAlg has been substituted by
4
2 2
4. Conclusion
the hydrophobic alkyl tertiary amine chain. Formation of the bicar-
Through grafting aliphatic tertiary amine (N,N-diethyl-
◦
bonate salts was achieved when CO was bubbled at 5 C for 30 min
hexylamine) onto water soluble NaAlg, a novel CO /N2 switchable
2
2
through the solution, the conductivity increased. And it decreased
surfactant (HDEA-Alg) have been successfully synthesized. The
grafting rate is 12.8% calculated according to the content of nitro-
gen by elemental analysis. The aqueous solutions of HDEA-Alg
◦
again after bubbling with N2 at 50 C for 30 min. The CO /N cycle
2
2
was performed three times to demonstrate the repeatability of the
switching process, and there is no discernible loss in performance
as shown in Fig. 5b. Both surface tension and conductivity analy-
sis demonstrated CO /N -responsive performance of HDEA-Alg in
were proved to be CO /N2 responsive. Employing this surfactant,
2
we prepared reversibly emulsion to use CO /N2 as a “green” trig-
2
ger. This work represents an innovative approach in developing
alginate smart materials.
2
2
aqueous solution.
7
6
6
5
5
4
4
0
5
0
5
0
5
0
a
60
NaAlg
b
HDEA-Alg
5
5
CO2
CO2
CO2
50
N2
N2
N2
4
5
40
0
.0
0.4
0.8
2
1.2
)
1.6
0
30 60 90 120 150 180
-
C
(×10 g/mL
Time(min)
Fig. 4. Surface tension of NaAlg and HDEA-Alg aqueous solutions (a) and reversible change of the solution surface tension of HDEA-Alg (0.4 wt%) when purging with CO2 and
N2, respectively (b).

J. Yang, H. Dong / Carbohydrate Polymers 153 (2016) 1–6
5
Fig. 5. Conductivity of NaAlg and HDEA-Alg aqueous solutions (a) and reversible change of the solution conductivity of HDEA-Alg (0.4 wt%) when purging with CO2 and N2,
respectively (b).
Fig. 6. Digital photographs of paraffin liquid-in-water emulsions (3/7, v/v) stabilized by HDEA-Alg, that were taken one week after preparation. The HDEA-Alg concentrations
◦
◦
in water from a to d are 0.4, 0.6, 0.8, 1.0 wt%; Bubbling CO2 through the emulsion d at 5 C for 30 min (e), then bubbling N2 through the emulsion e at 50 C for 30 min, followed
by re-homogenization for 3 min, 24 h later (f); The fluorescence photomicrograph of the emulsion d (g) and e (h).
Acknowledgements
Hu, Y. M., Ge, L. L., Han, J., & Guo, R. (2015). Concentration and temperature
induced dual-responsive wormlike micelle to hydrogel transition in ionic
liquid-type surfactant [C16imC9]Br aqueous solution without additives. Soft
Matter, 11, 5624–5631.
Jessop, P. G., Phan, L., Carrier, A., Robinson, S., DÜrr, C. J., & Harjani, J. R. (2010). A
solvent having switchable hydrophilicity. Green Chemistry, 12, 809–814.
Jessop, P. G., Mercera, S. M., & Heldebrant, D. J. (2012). CO2-triggered switchable
solvents, surfactants, and other materials. Energy & Environmental Science, 5,
7240–7253.
Jiang, J. Z., Zhu, Z. Y., Cui, Z. G., & Binks, B. P. (2013). Switchable pickering emulsions
stabilized by silica nanoparticles hydrophobized in situ with a switchable
surfactant. Angewandte Chemie International Edition, 52, 12373–12376.
Jochumab, F. D., & Theato, P. (2013). Temperature- and light-responsive smart
polymer materials. Chemical Society Reviews, 42(17), 7468–7483.
Lin, S. J., & Theato, P. (2013). CO2-responsive polymers. Macromolecular Rapid
Communications, 34, 1118–1133.
Liu, Y. X., Jessop, P. G., Cunningham, M., Eckert, C. A., & Liotta, C. L. (2006).
Switchable surfactants. Science, 313, 958–960.
Liu, H., Wang, C. Y., Zou, S. W., Wei, Z. J., & Tong, Z. (2012). Simple, reversible
emulsion system switched by pH on the basis of chitosan without any
hydrophobic modification. Langmuir, 28, 11017–11024.
Liu, P. W., Lu, W. Q., Wang, W. J., Li, B. G., & Zhu, S. P. (2014). Highly CO2/N2
switchable zwitterionic surfactant for pickering emulsions at ambient
temperature. Langmuir, 30, 10248–10255.
Melle, S., Lask, M., & Fuller, G. G. (2005). Pickering emulsions with controllable
stability. Langmuir, 21, 2158–2162.
Authors gratefully acknowledge the financial support from a
project funded by the Priority Academic Program Development
of Jiangsu Higher Education Institutions, Postgraduate Innovation
Project of Jiangsu Province (KYLX15 1359), Natural Science Foun-
dation of Yangzhou (yz2014066), and the devices support from
testing center of Yangzhou University.
References
Albrecht, M., Ehrler, S., & Mühlebach, A. (2003). Nanocomposites from layered
silicates: Graft polymerization with intercalated ammonium peroxides.
Macromolecular Rapid Communications, 24, 382–387.
Cheng, Z., Ren, B. y., Gao, M., Liu, X. X., & Tong, Z. (2007). Ionic self-assembled
redox-active polyelectrolyte-ferrocenyl surfactant complexes: Mesomorphous
structure and electrochemical behavior. Macromolecules, 40, 7638–7643.
Czaun, M., Hevesi, L., Takafuji, M., & Ihara, H. (2008). A novel approach to
magneto-responsive polymeric gels assisted by iron nanoparticles as nano
cross-linkers. Chemical Communication, 2124–2126.
Fowler, C. I., Muchemu, C. M., Miller, R. E., Phan, L., O’Neill, C., Jessop, P. G., et al.
(
2011). Emulsion polymerization of styrene and methyl methacrylate using
Mirarefi, P., & Ted Lee, C., Jr. (2010). Photo-induced unfolding and inactivation of
bovine carbonic anhydrase in the presence of a photoresponsive surfactant.
Biochimica et Biophysica Acta, 1804, 106–114.
Pocoví-Martínez, S., Francés-Soriano, L., Zaballos-Garca, E., Scaiano, J. C.,
González-Béjar, M., & Pérez-Prieto, J. (2013). CO2 switchable nanoparticles:
Reversible water/organicphase exchange of gold nanoparticles by gas
bubbling. RSC Advances, 3, 4867–4871.
cationic switchable surfactants. Macromolecules, 44, 2501–2509.
Ge, L. L., Shao, W. Q., Lu, S. H., & Guo, R. (2014). Droplet topology control of Janus
emulsion prepared in one-step high energy mixing. Soft Matter, 10, 4498–4505.
Ghosh, S., Irvin, K., & Thayumanavan, S. (2007). Tunable disassembly of micelles
using a redox trigger. Langmuir, 23, 7916–7919.
Han, D. H., Tong, X., Boissie r` e, O., & Zhao, Y. (2012). General strategy for making
CO2-switchable polymers. ACS Macro Letters, 1, 57–61.

6
J. Yang, H. Dong / Carbohydrate Polymers 153 (2016) 1–6
Qian, Y., Zhang, Q., Qiu, X. Q., & Zhu, S. P. (2014). CO2-responsive
Zhang, Q., Yu, G. Q., Wang, W. J., Li, B. G., & Zhu, S. P. (2012). Preparation of
CO2/N2-triggered reversibly coagulatable and redispersible polyacrylate
latexes by emulsion polymerization using a polymeric surfactant.
Macromolecular Rapid Communications, 33, 916–921.
diethylaminoethyl-modified lignin nanoparticles and their application as
surfactants for CO2/N2-switchable pickering emulsions. Green Chemistry, 16,
4
963–4968.
Xu, L. Q., Zhang, B., Sun, M., Hong, L., Neoh, K. G., Kang, E. T., et al. (2013).
CO2-triggered fluorescence turn-on response of perylene diimide-containing
poly(N,N-dimethylaminoethyl methacrylate). Journal of Materials Chemistry A,
Zoppe, J. O., Venditti, R. A., & Rojas, O. J. (2012). Pickering emulsions stabilized by
cellulose nanocrystals grafted with thermo-responsive polymer brushes.
Journal of Colloid and Interface Science, 369(1), 202–209.
1
, 1207–1212.
Yang, J. S., Zhou, Q. Q., & He, W. (2013). Amphipathicity and self-assembly behavior
of amphiphilic alginate esters. Carbohydrate Polymers, 92, 223–227.