High-Performance Double-Network Ion Gels with Fast Thermal Healing Capability via Dynamic Covalent Bonds

Article abstract of DOI:10.1021/acs.chemmater.8b03104

A tough double-network (DN) ion gel composed of chemically cross-linked poly(furfuryl methacrylate-co-methyl methacrylate) (P(FMA-co-MMA)) and physically cross-linked poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-co-HFP)) networks with 80 wt % of ionic liquid (IL) was fabricated via a one-pot method. This ion gel exhibits excellent mechanical strength and considerable ionic conductivity, which can be used as a solid gel electrolyte. Upon an adjustment of the weight ratio of P(FMA-co-MMA) to P(VDF-co-HFP) and the content of the cross-linker, remarkably robust DN ion gel (failure tensile stress 660 kPa, strain 268%; failure compressive stress 17 MPa, strain 85%) was obtained. The high mechanical strength is attributed to the chemical/physical interpenetrating networks. The rigid chemically cross-linked P(FMA-co-MMA) network dissipates most of the loading energy, and the ductile physically cross-linked P(VDF-co-HFP) network provides stretchability for the whole gel. More importantly, the P(FMA-co-MMA) network is formed by dynamic covalent bonds that can undergo a thermally reversible reaction, giving the gel a unique and effective thermal healing capability. Furthermore, with the high content of IL, the DN ion gel possesses a high ionic conductivity of 3.3 mS cm^-1 at room temperature, which is higher than those of most solid polymer electrolytes and comparable to those of commercial organic liquid electrolytes.

Full text of DOI:10.1021/acs.chemmater.8b03104

Subscriber access provided by The University of Texas at El Paso (UTEP)
Article
High-Performance Double-Network Ion Gels with Fast
Thermal Healing Capability via Dynamic Covalent Bonds
Zhehao Tang, Xiaolin Lyu, Anqi Xiao, Zhihao Shen, and Xinghe Fan
Chem. Mater., Just Accepted Manuscript • Publication Date (Web): 16 Oct 2018
Downloaded from http://pubs.acs.org on October 16, 2018
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 12
Chemistry of Materials
1
2
3
4
5
6
7
High-Performance Double-Network Ion Gels with Fast Thermal
Healing Capability via Dynamic Covalent Bonds
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Zhehao Tang, Xiaolin Lyu, Anqi Xiao, Zhihao Shen* and Xinghe Fan*
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of Ministry
of Education, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China
ABSTRACT:
A
tough double-network (DN) ion gel composed of chemically crosslinked poly(furfuryl
methacrylate) (P(FMA-co-MMA)) and physically crosslinked poly(vinylidene
methacrylate-co-methyl
fluoride-co-hexafluoropropylene) (P(VDF-co-HFP)) networks with 80 wt% of ionic liquid (IL) was fabricated via a one-pot
method. This ion gel exhibits excellent mechanical strength and considerable ionic conductivity, which can be used as a
solid gel electrolyte. By adjusting the weight ratio of P(FMA-co-MMA) to P(VDF-co-HFP) and the content of the
crosslinker, remarkably robust DN ion gel (failure tensile stress 660 kPa, strain 268%; failure compressive stress 17 MPa,
strain 85%) was obtained. The high mechanical strength is attributed to the chemical/physical interpenetrating networks.
The rigid chemically crosslinked P(FMA-co-MMA) network dissipates most of the loading energy, and the ductile
physically crosslinked P(VDF-co-HFP) network provides stretchability for the whole gel. More importantly, the
P(FMA-co-MMA) network is formed by dynamic covalent bonds that can undergo a thermally reversible reaction, giving
the gel a unique and effective thermal healing capability. Furthermore, with the high content of IL, the DN ion gel
possesses a high ionic conductivity of 3.3 mS cm1 at room temperature, which is higher than those of most solid polymer
electrolytes and comparable to commercial organic liquid electrolytes.
better flexibility, but their ionic conductivity is relatively
INTRODUCTION
poor.7-9 Researchers are striving to find new materials that
In the past two decades, great progresses have been
combine excellent flexibility and outstanding electrical
achieved on smart devices like smart phones, home
performance.
automation, and wearable devices. Many impressive
Ionic liquids (ILs),10-11 mostly composed of inorganic
advances in electronic technology have led to the
cations and organic anions, maintain the liquid state at
development of thinner, lighter, and softer smart devices.1
room temperature. They have attracted much interest
Significantly, flexible electronics such as artificial e-skin,2
owing to their high ionic conductivity, wide
flexible display,3 and flexible energy storage devices,4-5 are
electrochemical window, and outstanding stability (both
the next generation of electronic devices and may bring a
electrochemical and thermal). More importantly, ILs have
new electronic technology revolution. The key
negligible vapor pressures and are non-flammable, which
components of flexible devices are flexible materials.
greatly improves the safety in use. Mixing ILs with
Although
traditional
inorganic
conductors
and
crosslinked polymers,12-14 low-molecular-weight organic
gelators,15-16 or inorganic scaffold,17-18 can produce ion gels
with both flexibility and excellent electrical properties.
Many new flexible electrical devices containing ion gels
have demonstrated their own special properties and
semiconductors can be constructed into structures of
wavy patterns, buckles, and others to realize satisfactory
stretchability through geometric designs, the complex
construction processes limit their applications.6 As an
alternative, soft solid polymer electrolytes (SPEs) have
applied
ACS Paragon Plus Environment
in
electrochromic
devices,19-20

Chemistry of Materials
solid-state polytetrafluoroethylene (PTFE) mold instead of
Page 2 of 12
electrochemiluminescent
devices,21
a
1
2
3
4
5
6
7
8
electrolytes,22 etc. However, the ion gels obtained in early
studies were easily broken attributed to their fragile
structures, which limits their preparation and applications.
Researchers have studied and developed a variety of
strategies to increase the strength of ion gels.23-25
completely sealed reactor, which is favorable for mass
production. Third, because of the thermal-reversible
dynamic covalent furan-maleimide bond, the gel
containing this network underwent a transition from the
static state to the dynamic state with increasing
37
temperature and showed the ability of thermal healing.
The construction of a double-network (DN) polymer
framework can significantly increase the mechanical
strength of the hydrogels, which was first proposed by
Gong et al. in 2003.26 Meanwhile, the unique
characteristics of various functional networks can also
give the resulting gels many outstanding features, such as
self-healing,27 shape memory,28 super adhesion,29 and so
on. Based on such a design, many researchers have
introduced DN structures into ion gels and successfully
prepared some high-performance DN ion gels.30-36 They
used the two-step in-situ free-radical polymerization that
9
Therefore, this kind of DN ion gel that can be simply
prepared will become a new type of high-strength,
recyclable and repairable soft material.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
EXPERIMENTAL SECTION
Materials
Methyl methacrylate (MMA, 98%) was purchased from
Beijing Yili Fine Chemicals and purified by neutral
alumina column chromatography to remove the inhibitor.
Poly(vinylidene
fluoride-co-hexafluoropropylene)
(P(VDF-co-HFP)) was purchased from Sigma-Aldrich.
Bromoethane (99%) and furfuryl alcohol (97%) were
purchased from Aladdin. Methacryloyl chloride (97%),
N,N'-(4,4'-diphenylmethane)bismaleimide (BMI, 98%),
is
easy
to
operate
or
to
combine
with
low-molecular-weight gelators or inorganic particles to
construct double-network structures. These results
indicate that this strategy can greatly and easily improve
the mechanical properties of ion gels.
and
1-Ethyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI], 98%)
were purchased from Energy Chemical. All reagents were
used as received without purification unless otherwise
noted.
Herein, we report a new kind of high-performance and
thermal-healable DN ion gel containing two
interpenetrating networks: the rigid and brittle chemically
crosslinked
poly(furfuryl
methacrylate-co-methyl
Synthesis of furan-2-ylmethyl methacrylate (FMA)
methacrylate) (P(FMA-co-MMA)) as the first network; the
soft and ductile physically crosslinked poly(vinylidene
fluoride-co-hexafluoropropylene) (P(VDF-co-HFP)) as the
second network (Figure 1a). We utilized the thermally
reversible Diels-Alder (DA) reaction between furan
moieties on the side chain and a multi-maleimide
crosslinker to construct the chemically crosslinked
network. While P(VDF-co-HFP) is a widely used soft
material and is able to form gels in many solvents, its high
molecular weight and flexible chain structure give it good
stretchability and flexibility. Our design was based on the
following considerations. First, P(FMA-co-MMA) has
good solubility in ILs.12 There is no macroscopic phase
separation between the polymer and the matrix. Second,
the monomer can be easily synthesized and the DA
reaction is highly resistant to water and oxygen. Therefore,
the preparation of the DN ion gel can be facilely realized
Furfuryl alcohol (1.00 eq, 9.81 g, 0.100 mol) and
triethylamine (1.50 eq, 15.2 g, 0.150 mol) were dissolved in
DCM (100 mL). Then the mixture was stirred at 0 oC for 30
min. A dry DCM solution of methacryloyl chloride (1.50 eq,
15.6 g, 0.150 mol) was added dropwise slowly. The mixture
o
was stirred at 0 C for another 1 h, and then the reaction
was allowed to proceed at ambient temperature for 12 h.
Afterward, the mixed solution was filtered to remove the
trimethylamine salt. The filtrate was washed with 100 mL
of distilled water for three times and then dried with
anhydrous sodium sulfate. The solution was concentrated
under a reduced pressure to give the crude product. The
purified product was obtained by silica gel column
chromatography with n-hexane/ethyl acetate (10:1, v/v) as
1
eluent to give a colorless liquid. Yield: 82%. H NMR (400
MHz, CDCl3, δ, ppm): 1.95 (t, 3H), 5.14 (s, 2H), 5.58 (t, 1H),
6.13 (t, 1H), 6.36 (m, 1H), 6.42 (d, 1H), 7.43 (m, 1H).
by
a
simple, one-pot method using
a
common
ACS Paragon Plus Environment

Page 3 of 12
Chemistry of Materials
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. The P(FMA-co-MMA)/P(VDF-co-HFP)/[EMIM][TFSI] DN ion gel. (a) Schematic illustrations of the composition of the
DN structure and its change after stretching; (b) Photograph of a large DN ion gel thin film with a diameter of 7 cm; (c)
Photograph of the abbreviation of Peking University made of the DN ion gel; (d) Photograph of a cylindrical DN ion gel with a
height of 1 cm and a diameter of 1.3 cm. (Logos in b and c Copyright 2018 Peking University)
The high-performance DN ion gel was prepared
through a one-pot method (Figure S3 in Supporting
Information). It mainly comprises the following steps. At
Synthesis of P(FMA-co-MMA)
P(FMA-co-MMA) was synthesized by reversible
addition-fragmentation
chain
transfer
(RAFT)
first,
calculated
amounts
of
P(FMA-co-MMA),
polymerization. The chain transfer agent (CTA),
(S)-1-dodecyl-(S)-(α,α-dimethyl-α-aceticacid)-trithiocar
bonate, was synthesized following a reported procedure.38
P(VDF-co-HFP), and the crosslinker BMI were dissolved
in acetone. After mixing with an appropriate amount of IL
([EMIM][TFSI]) and stirring for 4 h, the solution was
poured into a PTFE mold, and acetone was volatilized at
room temperature. Finally, we successfully obtained the
high-strength DN ion gel by heating the precursor at 70
oC for 24 h to form complete the furan- maleimide DA
crosslinking reaction (Scheme 1). Taking advantages of the
simple preparation process, we were able to fabricate a
variety of DN ion gels having different shapes with the
mold (parts b, c, and d of Figure 1). The prepared DN ion
gel shows a smooth and dense surface without pores. We
used small-angle X-ray scattering (SAXS) and differential
scanning calorimetry (DSC) to investigate the
homogeneity of the DN ion gels prepared through
solution blending. Compared to the P(VDF-co-HFP) SN
ion gel, there is no additional enhancement in the
scattering intensity of the sample when the two polymers
are mixed together (Figure S4 in Supporting Information).
The DSC thermograms only show a single glass transition
process in the low temperature region (Figure S5 in
Supporting Information). Moreover, visible macroscopic
phase separation did not occur in the samples without
CTA
(1.00
eq,
182
mg,
0.500
mmol),
2,2'-azobis(2-methylpropionitrile) (AIBN, 0.300 eq, 28.0
mg, 0.170 mmol), MMA (150 eq, 7.50 g, 75.0 mmol), and
the synthesized FMA (50.0 eq, 4.15 g, 25.0 mmol) were
dissolved in 20 mL of dioxane and then transferred into a
dry polymerization tube. After being dehydrated and
deoxygenated by freeze-pump-thaw cycles for three times,
the polymerization tube was sealed with gas fire. The
reaction was allowed to proceed at 70 oC for 18 h. The tube
was immersed into liquid nitrogen to terminate the
reaction. The mixture was precipitated by adding into 500
mL of methanol for three times to obtain a pale yellow
solid. The precipitate was filtered and dried under
o
vacuum at 60 C overnight. The molecular weight (MW)
and MW dispersity (ĐM) were measured by gel
permeation chromatography (GPC, Waters, 2414) with
tetrahydrofuran (THF) as eluent (Figure S1 in Supporting
Information). The molar ratio of FMA to MMA was
determined by 1H NMR (Figure S2 in Supporting
Information).
Preparation of the DN ion gels
ACS Paragon Plus Environment

Chemistry of Materials
crosslinkers for over ten days (Figure S6 and S7 in Table 1. Gelation time of P(FMA-co-MMA) ion gels
Page 4 of 12
1
2
3
4
Supporting Information).
Mn (Da)
FMA:MMA b)
Gelation time (min)
a)
5
6
7
8
9
Sample-1
Sample-2
Sample-3
Sample-4
Sample-5
25600
22100
22100
20200
20600
1:1
1:3
1:5
1:7
1:12
13
19
47
93
∞
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 1. Furan-maleimide DA crosslinking reaction.
RESULTS AND DISCUSSION
Gelation Time of P(FMA-co-MMA) Ion Gels
A series of P(FMA-co-MMA) samples were synthesized
a) Determined by GPC; b) Determined by 1H NMR.
The sample film was cut into cm long,
by reversible addition-fragmentation chain transfer (RAFT)
1
a
2
polymerization and characterized by GPC and H NMR
dumb-bell-shaped testing sample with a length of 4 mm
at the narrowest position. Then the tensile stress–strain
curves were obtained by stretching the sample at a rate of
5 mm min1. As shown in Figure 2a, with increasing degree
of crosslinking, the ion gel film will be tougher, and the
elastic modulus (represented by the slope of the curve)
will improve because of the enhancement of the rigid
structure. However, the highly crosslinked network will
weaken the chain entanglement of the second network,
and it reduces the stretchability of the gel. Meanwhile,
adding insufficient amount of the crosslinking agent
cannot form a complete skeleton structure. Therefore, it is
important to choose an appropriate crosslinker content.
(Figure S1 and S2 in Supporting Information). Results
show that polymers with different molar ratios of FMA to
MMA have number-averaged molecular weights (Mn’s) of
about 20000 Da with unimodal distributions. Meanwhile,
the polymers synthesized are random copolymers, as
demonstrated by DSC results (Figure S8 in Supporting
Information). Detailed data are shown in Table S1. Before
the preparation of the DN ion gel, we need to confirm
that a stable ion gel can be formed through the DA
reaction by using this kind of polymer containing the
furan moiety. The polymer and the crosslinker were
dissolved in an appropriate amount of ionic liquid (with
constant concentrations of the polymer and the
crosslinker). After being heated up to 70 oC for a while, all
of the mixture solutions gelled except the polymer with an
FMA:MMA molar ratio of 1:12, and the gelation time
decreases greatly with increasing content of the furan
moiety owing to the increasing number of reaction sites in
the solution (Table 1). We chose the polymer with an
FMA:MMA molar ratio of 1:3 to prepare the DN ion gels
because it can form a gel in just 20 min and the cost is
lower than sample 1 due to the less content of FMA. The
DN ion gel samples prepared in this work were all based
on Sample-3.
Figure 2. Comparison of tensile stress–strain curves of DN
ion gels with different crosslinker loadings (a) and different
mass ratios of the two networks (b).
The P(FMA-co-MMA)/P(VDF-co-HFP) mass ratio (r) is
also a key parameter. A series of DN ion gels with
different r values were prepared. The results of the tensile
tests indicate that the DN ion gel will be more rigid with
increasing content of P(VDF-co-HFP) owing to the higher
density of the crystalline region of the PVDF segments
(Figure 2b). However, it is not beneficial to the formation
Mechanical Properties and Toughening Mechanisms
The strategy of constructing the double-network can
greatly improve the mechanical strength of the gel. We
maintained the IL mass fraction of 80% and investigated
the effect of the composition of polymer network on the
mechanical properties. The film tensile tests were
conducted with a universal testing system (5567, Instron).
ACS Paragon Plus Environment

Page 5 of 12
Chemistry of Materials
of interpenetrating structures when any component is Like other DN ion gels and DN hydrogels, the high
1
2
3
4
5
6
7
8
excessive. It is worth noting that the mechanical
properties of the ion gel prepared can be controlled by
adjusting the amount of each component of the gel. For
example, to meet the demands of flexible electrical
devices for relatively high toughness and stretchability,
the degree of crosslinking and the content of
P(VDF-co-HFP) can be appropriately reduced. Such an
adjustability indicates that the gel is a designable material.
Finally, the optimal composition of the toughest DN ion
mechanical strength can be mainly attributed to the two
interpenetrating networks.39-40 P(FMA-co-MMA) was
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
gel
was
determined
to
be
P(FMA-co-MMA):P(VDF-co-HFP):BMI = 100:100:5 (mass
ratio).
The toughest DN ion gel has excellent stretchability
with the tensile fracture strain of 268% (parts a and b of
Figure 3 and Video VSI1 in Supporting Information),
which is about 10 times higher than their individual
single-network (SN) counterparts and is similar to those
of other DN ion gels that have been reported in the
literature such as the inorganic/organic DN ion gel (about
300% strain).31 The failure tensile stress of the DN ion gel
prepared is approximately 660 kPa, which is substantially
higher than those of most DN ion gels reported in the
literature.30-32 It can be attributed to the high
entanglement of the P(VDF-co-HFP) chains. Figure S9
shows the cyclic tensile behaviors of the DN and SN ion
gels. It indicates that adding another chemically
crosslinked network into the P(VDF-co-HFP) SN ion gel
could resist the deformation during the tensile test. The
DN ion gel could easily recover to its original length at a
relatively small loading.
Figure 3. Mechanical properties of the DN ion gels. (a)
Tensile stress–strain curves of DN and respective SN ion gels;
(b) Photographs of the dumb-bell-shaped DN ion gel film
before and after stretching; (c) Compressive stress–strain
curves of DN and respective SN ion gels; (d). Photographs of
a
cylindrical DN ion gel before, during, and after
compression.
crosslinked by the reaction between furan and maleimide.
Owing to the low molecular weight (MW), the SN
P(FMA-co-MMA) ion gel shows a poor mechanical
strength (parts a and c of Figure 3) and is easily broken
(Figure S10b in Supporting Information). However, this
SN ion gel can maintain its origin shape and is difficult to
deform because of its chemical crosslinking bonds.
P(VDF-co-HFP) has excellent tensile strength.41-42 When it
is mixed with ILs, part of the short PVDF segments will
crystallize, with the crystals acting as physical crosslinking
points to form a physical gel.43-44 Although such a gel
shows good mechanical properties at a high polymer
concentration, the maximum elongation decreases rapidly
when the content of IL is above 40 wt%.43 More
importantly, the P(VDF-co-HFP) SN ion gel is like a
“sponge”, which means that it cannot hold the IL well. For
example, the masses of a cylindrical sample before and
after compression are 1.6 g and 0.9 g, respectively. Most of
the IL was pushed out, and the gel was deformed severely
(Figure S10c in Supporting Information).
Moreover, the cylindrical gel also has excellent
compressive properties. The compressive tests were
conducted with a universal testing system (UTM4104,
Kasontest). The compressive stress–strain curves were
obtained by compressing a cylindrical sample with a
height of 1 cm and a diameter of 1.3 cm at a rate of 5 mm
min1. The result shows that the gel obtained has the
failure compressive stress of more than 17 MPa at 85%
strain (parts c and d of Figure 3), which is comparable to
that of other high-performance ion gels (7.7 MPa at 92%
strain),30 and it is not easily deformed (Figure S10a in
Supporting Information).
ACS Paragon Plus Environment

Chemistry of Materials
Page 6 of 12
Combining the two networks can overcome these process to complete the repair. Each of the samples with
1
shortcomings. These two networks can be dispersed
evenly in the DN ion gel prepared through the sol-gel
transition. The rigid P(FMA-co-MMA) network acts as a
support structure, while the ductile P(VDF-co-HFP)
polymer chains are intertwined with each other. When
this tough gel is stretched by the applied force, the brittle
chemically crosslinked network ruptures first and
dissipates most of the energy. The soft physically
crosslinked network serves as “hidden length” to maintain
the integrity of the broken first network.39 It is like the
“fences and ropes”: a pile of fences are easy to be
separated; after intertwined with a bundle of ropes, they
can be extremely strong.
different sizes has a remarkable healing speed. The
cracked film sample healed itself in just 10 s (Figure 4 and
Video VSI2 in Supporting Information). The entire
thermal healing process of the DN ion gel film was clearly
observed through an optical microscope (Olympus BX-51,
Instec).
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Thermal healing capability
Because of the excellent thermal stability of the IL, the
5% weight loss (thermal decomposition) temperature of
the DN ion gel obtained is above 350 oC under nitrogen or
air (Figure S11 in Supporting Information). The IL is also
nonflammable. Therefore, the DN ion gel can improve the
safety and extend the operating temperature effectively
when used in flexible electronics. Benefiting from the
excellent thermal stability, some unique properties of the
gel at high temperatures can be studied.
Figure 4. Thermal healing process of the DN ion gel film. (a)
Photographs of the cut film which was healed after being
heated at 100 oC for 20 s; (b) Optical micrographs of the
healing process at 100 oC for 10 s.
First, we investigate the thermal healing capability of
the DN ion gel films. After being cut, the film sample was
o
attached to each other and heated to 100 C. Under this
The P(VDF-co-HFP) SN ion gel is a physical gel and can
undergo a sol-gel transition owing to its thermal
reversibility in that the PVDF crystalline regions melt
when being heated and re-form upon cooling.43 For
P(FMA-co-MMA) SN ion gels, increasing temperature will
cause the cleavage of the introduced furan-maleimide
dynamic bonds, and part of the chemically crosslinked
network will break. Consequently, this SN ion gel will
transform from a static state into a dynamic state. Such
kind of crosslinked system is widely used in thermal
condition, the gels can enter into a dynamic state in
which the polymer chains have a higher mobility. The gels
will interpenetrate with each other to eliminate the
interface, and the network will re-form during the cooling
process to complete the repair. Each of the samples with
different sizes has a remarkable healing speed. The
cracked film sample healed itself in just 10 s (Figure 4 and
Video VSI2 in Supporting Information). The entire
thermal healing process of the DN ion gel film was clearly
observed through an optical microscope (Olympus BX-51,
Instec).
healing
materials
owing
to
its
controllable
bonding-breaking process.45-47 Because of the thermally
induced de-crosslinking and re-crosslinking processes, the
DN ion gel has the ability to heal the defects.
To prove that dynamic covalent bond plays an
important role in the thermal healing process. Rotational
rheometer was used to investigate the thermo-rheological
behaviors of the DN ion gels prepared. A plate rotor with
a diameter of 2.5 cm was used to test the temperature
First, we investigate the thermal healing capability of
the DN ion gel films. After being cut, the film sample was
o
attached to each other and heated to 100 C. Under this
o
dependencies of G and G at a heating rate of 2 C min1
condition, the gels can enter into a dynamic state in
which the polymer chains have a higher mobility. The gels
will interpenetrate with each other to eliminate the
interface, and the network will re-form during the cooling
and a frequency of 1 Hz. As shown in Figure 5a, the
storage modulus G decreases dramatically when
o
o
temperature is increased from 100 C to 120 C, and G
ACS Paragon Plus Environment

Page 7 of 12
Chemistry of Materials
completely disappeared (Figure 6a). For the strip samples,
starts to be lower than the loss modulus G at 110 oC. This
1
indicates that the DN ion gel undergoes a sol-gel
transition in this temperature range. To further prove that
the transition is attributed to the de-crosslinking of the
dynamic network, the temperature dependencies of G
and G of the P(FMA-co-MMA) SN ion gels and the
PMMA SN ion gels , as a contrast, were investigated. The
results show that the P(FMA-co-MMA) gel exhibits the
sol-gel thermal transition behavior (Figure 5b), while the
PMMA gel remains in the gelled state on heating, and the
crack still existed after 150 min (Figure 5c). The transition
of the DN ion gel was also studied by differential scanning
calorimetry (DSC). There are two main endothermic
processes in the thermogram (Figure 5d). According to
the literature on the P(VDF-co-HFP) SN ion gel, the peak
the healed gel could be bent freely and withstand a
certain strain (Figure 6b). The cut gels were dyed in
different colors for easy observation of the healing process.
For the healed gel, different colors permeate each other at
the interfaces, proving that the DN ion gel does enter a
dynamic state at high temperatures.
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
o
at around 80 C can be attributed to the melting of the
PVDF crystal.43 The peak originating from the reverse DA
reaction is at 110 oC, consistent with rheological results.
Figure 6. Thermal healing capability of the DN ion gel. (a)
Three fan-shaped DN ion gels, which were dyed into three
o
colors, fusing together into a cylindrical at 100 C for 10 min,
with the healed cylindrical sample without cracks; (b) Three
o
dyed DN ion gel strips fusing together at 100 C for 10 min,
with the healed strip sample being able to be bent and hold a
weight of 50 g.
Figure 5. Thermal properties of the DN ion gel in the heating
process. (a, b, c) Temperature dependencies of shear storage
modulus G and shear loss modulus G of the DN ion gel (a),
P(FMA-co-MMA) (b) and PMMA (c) SN ion gels. (d) DSC
thermogram of the DN ion gel at a heating rate of 20 °C min1
under a nitrogen atmosphere.
The above results demonstrate that the DN ion gel
containing a dynamic crosslinking network possesses
attractive thermal healing capability and can be served as
a “smart” material. For example, using this repairable gel
as a gel polymer electrolyte should be able to help
improve the service life of the products. More importantly,
because of the reparability, the gel is recyclable, which is
also more environmentally friendly.
In the same way, we also tested the thermal healing
capability of bulk samples. Because of poorer heat
conduction and larger areas to repair, the cylindrical and
strip samples needed more time to realize complete
healing. However, the results were satisfactory. There was
no significant difference in the macroscopic appearance of
the samples before and after the healing, and the cracks
Ionic conductivity of the DN ion gels
ILs have excellent electrical performance, and ion gels
are widely used in organic electrical devices. We also
conducted a preliminary study on the electrical properties
ACS Paragon Plus Environment

Chemistry of Materials
Page 8 of 12
of the DN ion gels prepared. The content of IL in the DN more rigid. With strengthening of the networks, the ionic
1
2
3
4
5
6
7
ion gel is as high as 80 wt%, leading to a very high ionic
conductivity, comparable to that of the neat
conductivity decreases due to the restricted transport of
free ions. However, the DN ion gel can still maintain a
high ionic conductivity. These excellent electrical
o
[EMIM][TFSI], which is 11 mS cm1 at 25 C.48 The ionic
conductivity of the ion gel was measured by using
electrochemical
impedance
spectroscopy
(EIS)
8
9
measurements. First, the film sample was cut into a circle
with a diameter of 1 cm to fit the circular electrode. Then
an electrochemical workstation (CHI 660E, CH
Instruments) was utilized to obtain the typical “Nyquist”
plot (Figure S12 in Supporting Information) with an AC
potential amplitude of 10 mV and a frequency range of 10
Hz–100 kHz. The intercept with the x-axis represents the
resistance of the ion gel. The ionic conductivity is
calculated by the following equation:
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
퐿
휎 = 푅 × 푆
(1)
where L and S represent the thickness and area of the film,
and R is the resistance. The DN ion gel exhibits attractive
ionic conductivity of around 1 mS cm1 in a wide
temperature range (Figure 7a), and the conductivity
shows no sharp decrease even at temperatures below 18
oC at which the IL [EMIM][TFSI] starts to freeze.48 The
DN scaffold plays an important role at low temperatures
to weaken the ionic interaction between [EMIM]+ and
[TFSI] and help keep the IL in the liquid state. Moreover,
the temperature dependence of conductivity can be fitted
quite well with the Vogel−Tammann−Fulcher (VTF)
equation (2) (Figure 7b).
Figure 7. Conductivity of the DN ion gel. (a) Ionic
conductivity of the DN ion gel from 40 oC to 80 oC; (b) VTF
fitting of the conductivity data; Conductivities of samples
with (c) different mass ratios of the two networks and (d)
different crosslinker loadings.
properties enable it to be potentially useful in energy
storage materials, electrochemical sensors, flexible devices,
and other fields.
CONCULSIONS
― 퐸a
In conclusion, we have successfully prepared a new type
of stretchable DN ion gel with excellent mechanical
strength, high ionic conductivity, and outstanding
thermal stability. This new DN ion gel is composed of a
chemically crosslinked P(FMA-co-MMA) network and a
physically crosslinked P(VDF-co-HFP) network and can
be prepared through a one-pot method under mild and
general conditions, which greatly simplifies the
preparation process. More importantly, the gel has the
capability of fast thermal healing attributed to the
dynamic covalent crosslinks based on thermal-reversible
DA reactions of the first network, which will help improve
the stability and reparability of electronic devices
containing this DN ion gel. Furthermore, the strategy for
designing and preparing smart ion gels with
functionalized polymer networks will promote the
휎 = 휎 × exp
(2)
(
)
0
푅(푇 ― 푇0)
where σ0 is the conductivity at infinite temperature, Ea is
the activation energy, and T0 is the temperature at which
molecular motion is frozen. Parameters of the VTF fitting
are provided in Table S2 of the Supporting Information.
The gel with the best mechanical strength (with a
crosslinker loading of 5 wt% and a ratio of the two
networks at 1:1) has a conductivity of 3.3 mS cm1 at room
temperature. Thus, it has the potential to be used in
flexible electronics because of its good flexibility and
conductivity even in harsh conditions.
The composition of the ion gel affects the electrical
properties slightly (parts c and d of Figure 7). Increasing
the content of the P(FMA-co-MMA) network and
improving the crosslinking degree can make the ion gels
ACS Paragon Plus Environment

Page 9 of 12
Chemistry of Materials
Amaratunga, G. A. J.; Milne, W. I., Flexible Electronics: The Next
development of “smart” soft materials. We can design new
1
2
3
4
5
6
7
8
Ubiquitous Platform. Proc. IEEE 2012, 100, 1486-1517.
(2) Chortos, A.; Bao, Z., Skin-inspired electronic devices. Mater.
Today. 2014, 17, 321-331.
types of ion gels with multiple stimuli-responsiveness
such as responses to force, electricity, and pH by changing
the segment sequence, side-chain group, and topological
structure. These functional ion gels will have a wide range
of applications in solid gel electrolytes, electrochemical
sensors, actuators, etc, and broaden the area of flexible
electronic.
(3) Rogers, J. A.; Bao, Z.; Baldwin, K.; Dodabalapur, A.; Crone, B.;
Raju, V. R.; Kuck, V.; Katz, H.; Amundson, K.; Ewing, J.; Drzaic,
P., Paper-like electronic displays: large-area rubber-stamped
plastic sheets of electronics and microencapsulated
electrophoretic inks. Proc. Natl. Acad. Sci. U. S. A. 2001, 98,
4835-40.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ASSOCIATED CONTENT
Supporting Information
(4) Zhao, Y.-f.; Zou, W.-j.; Li, H.; Lu, K.; Yan, W.; Wei, Z.-x.,
Large-area, flexible polymer solar cell based on silver nanowires
as transparent electrode by roll-to-roll printing. Chin. J. Polym.
Sci. 2016, 35, 261-268.
This Supporting Information is available free of charge via
the Internet at http://pubs.acs.org. Videos of tensile test and
thermal
healing
process.
Characterization
of
(5) Yao, B.; Zhang, J.; Kou, T.; Song, Y.; Liu, T.; Li, Y., Paper-Based
Electrodes for Flexible Energy Storage Devices. Adv. Sci. 2017, 4,
1700107.
P(FMA-co-MMA); cyclic tensile behaviors; photographs of
compressive test; surface topography; thermal stability;
“Nyquist” plot.
(6) Kim, D. H.; Xiao, J.; Song, J.; Huang, Y.; Rogers, J. A.,
Stretchable, curvilinear electronics based on inorganic materials.
Adv. Mater. 2010, 22, 2108-24.
AUTHOR INFORMATION
Corresponding Author
(7) Zhou, W.; Wang, S.; Li, Y.; Xin, S.; Manthiram, A.;
Goodenough, J. B., Plating a Dendrite-Free Lithium Anode with a
Polymer/Ceramic/Polymer Sandwich Electrolyte. J. Am. Chem.
Soc. 2016, 138, 9385-8.
*Zhihao Shen. E-mail: zshen@pku.edu.cn
*Xinghe Fan. E-mail: fanxh@pku.edu.cn
ORCID
Zhehao Tang: 0000-0002-1685-8664
Xiaolin Lyu: 0000-0003-4221-6806
Anqi Xiao: 0000-0002-6479-6381
Zhihao Shen: 0000-0003-2858-555X
Xinghe Fan: 0000-0002-0585-2558
Notes
(8) Ping, J.; Pan, H.; Hou, P. P.; Zhang, M. Y.; Wang, X.; Wang, C.;
Chen, J.; Wu, D.; Shen, Z.; Fan, X. H., Solid Polymer Electrolytes
with Excellent High-Temperature Properties Based on Brush
Block Copolymers Having Rigid Side Chains. ACS Appl. Mater.
Interfaces 2017, 9, 6130-6137.
(9) Lyu, Y.-F.; Zhang, Z.-J.; Liu, C.; Geng, Z.; Gao, L.-C.; Chen, Q.,
Random binary brush architecture enhances both ionic
conductivity and mechanical strength at room temperature. Chin.
J. Polym. Sci. 2017, 36, 78-84.
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This work was supported by the National Natural Science
Foundation of China (Grants 51473005 and 51725301).
(10) Plechkova, N. V.; Seddon, K. R., Applications of ionic liquids
in the chemical industry. Chem. Soc. Rev. 2008, 37, 123-50.
(11) Bonhôte, P.; Dias, A.-P.; Papageorgiou, N.; Kalyanasundaram,
ABBREVIATIONS
K.;
Grätzel,
M.,
Hydrophobic,
Highly
Conductive
DN, double-network; SN, single-network; IL, ionic liquid;
RAFT, reversible addition-fragmentation chain transfer; DSC,
differential scanning calorimetry; EIS, electrochemical
impedance spectroscopy
Ambient-Temperature Molten Salts†. Inorg. Chem. 1996, 35,
1168-1178.
(12) Susan, M. A.; Kaneko, T.; Noda, A.; Watanabe, M., Ion gels
prepared by in situ radical polymerization of vinyl monomers in
an ionic liquid and their characterization as polymer electrolytes.
J. Am. Chem. Soc. 2005, 127, 4976-83.
REFERENCES
(1) Nathan, A.; Ahnood, A.; Cole, M. T.; Sungsik, L.; Suzuki, Y.;
Hiralal, P.; Bonaccorso, F.; Hasan, T.; Garcia-Gancedo, L.;
Dyadyusha, A.; Haque, S.; Andrew, P.; Hofmann, S.; Moultrie, J.;
Daping, C.; Flewitt, A. J.; Ferrari, A. C.; Kelly, M. J.; Robertson, J.;
(13) Lodge, T. P., Materials science. A unique platform for
materials design. Science 2008, 321, 50-1.
(14) Zhang, Y.-D.; Fan, X.-H.; Shen, Z.; Zhou, Q.-F.,
ACS Paragon Plus Environment

Chemistry of Materials
Page 10 of 12
Thermoreversible Ion Gel with Tunable Modulus Self-Assembled
(27) Liu, S.; Li, L., Recoverable and Self-Healing Double Network
1
2
3
by a Liquid Crystalline Triblock Copolymer in Ionic Liquid.
Macromolecules 2015, 48, 4927-4935.
Hydrogel Based on kappa-Carrageenan. ACS Appl. Mater.
Interfaces 2016, 8, 29749-29758.
4
5
6
7
(15) Kimizuka, N.; Nakashima, T., Spontaneous Self-Assembly of
Glycolipid Bilayer Membranes in Sugar-philic Ionic Liquids and
Formation of Ionogels. Langmuir 2001, 17, 6759-6761.
(28) Le, X.; Lu, W.; Zheng, J.; Tong, D.; Zhao, N.; Ma, C.; Xiao, H.;
Zhang, J.; Huang, Y.; Chen, T., Stretchable supramolecular
hydrogels with triple shape memory effect. Chem. Sci. 2016, 7,
6715-6720.
8
(16) Tu, T.; Bao, X.; Assenmacher, W.; Peterlik, H.; Daniels, J.;
9
Dotz,
low-molecular-mass gelators for ionic liquids: synthesis,
aggregation and application of pyridine-bridged
K.
H.,
Efficient
air-stable
organometallic
(29) Li, J.; Celiz, A. D.; Yang, J.; Yang, Q.; Wamala, I.; Whyte, W.;
Seo, B. R.; Vasilyev, N. V.; Vlassak, J. J.; Suo, Z.; Mooney, D. J.,
Tough adhesives for diverse wet surfaces. Science 2017, 357,
378-381.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
bis(benzimidazolylidene)-palladium complexes. Chem.-Eur. J.
2009, 15, 1853-61.
(30) Ding, Y.; Zhang, J.; Chang, L.; Zhang, X.; Liu, H.; Jiang, L.,
Preparation of High-Performance Ionogels with Excellent
Transparency, Good Mechanical Strength, and High
Conductivity. Adv. Mater. 2017, 29, 1704253
(17) Fukushima, T.; Aida, T., Ionic liquids for soft functional
materials with carbon nanotubes. Chem.-Eur. J. 2007, 13, 5048-58.
(18) Torimoto, T.; Tsuda, T.; Okazaki, K.; Kuwabata, S., New
frontiers in materials science opened by ionic liquids. Adv. Mater.
2010, 22, 1196-221.
(31) Kamio, E.; Yasui, T.; Iida, Y.; Gong, J. P.; Matsuyama, H.,
Inorganic/Organic Double-Network Gels Containing Ionic
Liquids. Adv. Mater. 2017, 29, 1704118
(19) Moon, H. C.; Kim, C. H.; Lodge, T. P.; Frisbie, C. D.,
Multicolored, Low-Power, Flexible Electrochromic Devices Based
on Ion Gels. ACS Appl. Mater. Interfaces 2016, 8, 6252-60.
(20) Oh, H.; Seo, D. G.; Yun, T. Y.; Kim, C. Y.; Moon, H. C.,
Voltage-Tunable Multicolor, Sub-1.5 V, Flexible Electrochromic
Devices Based on Ion Gels. ACS Appl. Mater. Interfaces 2017, 9,
7658-7665.
(32) Moghadam, F.; Kamio, E.; Yoshizumi, A.; Matsuyama, H., An
amino acid ionic liquid-based tough ion gel membrane for CO2
capture. Chem. Commun. 2015, 51, 13658-61.
(33) Kataoka, T.; Ishioka, Y.; Mizuhata, M.; Minami, H.;
Maruyama, T., Highly Conductive Ionic-Liquid Gels Prepared
with Orthogonal Double Networks of a Low-Molecular-Weight
Gelator and Cross-Linked Polymer. ACS Appl. Mater. Interfaces
2015, 7, 23346-52.
(21) Moon, H. C.; Lodge, T. P.; Frisbie, C. D.,
Solution-processable electrochemiluminescent ion gels for
flexible, low-voltage, emissive displays on plastic. J. Am. Chem.
Soc. 2014, 136, 3705-12.
(34) Arafune, H.; Honma, S.; Morinaga, T.; Kamijo, T.; Miura, M.;
Furukawa, H.; Sato, T., Highly Robust and Low Frictional
Double-Network Ion Gel. Adv. Mater. Interfaces. 2017, 4,
1700074.
(22) Chen, N.; Dai, y.; Xing, Y.; Wang, L.; Guo, C.; Chen, R.; Guo,
S.; Wu, F., Biomimetic Ant-nest Ionogel Electrolyte Boosts the
Performance of Dendrite-free Lithium Batteries. Energy Environ.
Sci. 2017, 10 , 1660-1667.
(35) Moghadam, F.; Kamio, E.; Matsuyama, H., High CO2
separation performance of amino acid ionic liquid-based double
network ion gel membranes in low CO2 concentration gas
mixtures under humid conditions. J. Membr. Sci. 2017, 525,
290-297.
(23) Lodge, T. P.; Ueki, T., Mechanically Tunable, Readily
Processable Ion Gels by Self-Assembly of Block Copolymers in
Ionic Liquids. Acc. Chem. Res. 2016, 19, 2107-2114.
(24) Gu, Y.; Zhang, S.; Martinetti, L.; Lee, K. H.; McIntosh, L. D.;
Frisbie, C. D.; Lodge, T. P., High toughness, high conductivity
ion gels by sequential triblock copolymer self-assembly and
chemical cross-linking. J. Am. Chem. Soc. 2013, 135, 9652-5.
(25) Tang, B.; White, S. P.; Frisbie, C. D.; Lodge, T. P.,
Synergistic Increase in Ionic Conductivity and Modulus of
Triblock Copolymer Ion Gels. Macromolecules 2015, 48,
4942-4950.
(36) Moghadam, F.; Kamio, E.; Yoshioka, T.; Matsuyama, H., New
approach for the fabrication of double-network ion-gel
membranes with high CO 2 /N 2 separation performance based
on facilitated transport. J. Membr. Sci. 2017, 530, 166-175.
(37) Chen, X.; Dam, M. A.; Ono, K.; Mal, A.; Shen, H.; Nutt, S. R.;
Sheran, K.; Wudl, F., A thermally re-mendable cross-linked
polymeric material. Science 2002, 295, 1698-702.
(38) Lai, J. T.; Filla, D.; Shea, R., Functional Polymers from Novel
Carboxyl-Terminated Trithiocarbonates as Highly Efficient RAFT
Agents. Macromolecules 2002, 35, 6754-6756.
(26) Gong, J. P.; Katsuyama, Y.; Kurokawa, T.; Osada, Y.,
Double-Network Hydrogels with Extremely High Mechanical
Strength. Adv. Mater. 2003, 15, 1155-1158.
(39) Gong, J. P., Why are double network hydrogels so tough?
ACS Paragon Plus Environment

Page 11 of 12
Chemistry of Materials
Soft Matter 2010, 6, 2583, 2583-2590
(40) Haque, M. A.; Kurokawa, T.; Gong, J. P., Super tough double
1
2
network hydrogels and their application as biomaterials. Polymer
2012, 53, 1805-1822.
3
4
5
6
7
8
9
(41) Li, Z.; Su, G.; Wang, X.; Gao, D., Micro-porous
P(VDF-HFP)-based polymer electrolyte filled with AlO
nanoparticles. Solid State Ionics 2005, 176, 1903-1908.
(42) Ding, Y.; Zhang, P.; Long, Z.; Jiang, Y.; Xu, F.; Di, W., The
ionic conductivity and mechanical property of electrospun
P(VdF-HFP)/PMMA membranes for lithium ion batteries. J.
Membr. Sci. 2009, 329, 56-59.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(43) Jansen, J. C.; Friess, K.; Clarizia, G.; Schauer, J.; Izák, P., High
Ionic Liquid Content Polymeric Gel Membranes: Preparation and
Performance. Macromolecules 2011, 44, 39-45.
(44) Friess, K.; Jansen, J. C.; Bazzarelli, F.; Izák, P.; Jarmarová, V.;
Kačírková, M.; Schauer, J.; Clarizia, G.; Bernardo, P., High ionic
liquid content polymeric gel membranes: Correlation of
membrane structure with gas and vapour transport properties. J.
Membr. Sci. 2012, 415-416, 801-809.
(45) Zeng, C.; Seino, H.; Ren, J.; Hatanaka, K.; Yoshie, N.,
Bio-Based Furan Polymers with Self-Healing Ability.
Macromolecules 2013, 46, 1794-1802.
(46) Barthel, M. J.; Rudolph, T.; Teichler, A.; Paulus, R. M.; Vitz,
J.; Hoeppener, S.; Hager, M. D.; Schacher, F. H.; Schubert, U. S.,
Self-Healing Materials via Reversible Crosslinking of
Poly(ethylene
oxide)-Block-Poly(furfuryl
glycidyl
ether)
(PEO-b-PFGE) Block Copolymer Films. Adv. Funct. Mater. 2013,
23, 4921-4932.
(47) Fuhrmann, A.; Gostl, R.; Wendt, R.; Kotteritzsch, J.; Hager,
M. D.; Schubert, U. S.; Brademann-Jock, K.; Thunemann, A. F.;
Nochel, U.; Behl, M.; Hecht, S., Conditional repair by locally
switching the thermal healing capability of dynamic covalent
polymers with light. Nat. Commun. 2016, 7, 13623.
(48) Tokuda, H.; Tsuzuki, S.; Susan, M. A.; Hayamizu, K.;
Watanabe, M., How ionic are room-temperature ionic liquids?
An indicator of the physicochemical properties. J. Phys. Chem. B
2006, 110, 19593-600.
ACS Paragon Plus Environment

Chemistry of Materials
Page 12 of 12
1
2
3
Table of Contents Graphic
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment