S1
Supporting Information
Programmable and Sophisticated Shape-Memory Behavior via
Tailoring Spatial Distribution of Polymer Crosslinks
Yaxin Qiu1 Qianru Wanyan1 Wenting Zhang1 Suna Yin1 Defeng Wu1,2*
(1 School of Chemistry & Chemical Engineering, Yangzhou University, Jiangsu, 225002, P. R. China)
(2 Provincial Key Laboratories of Environmental Engineering & Materials, Jiangsu, 225002, P. R. China)
* Corresponding author, [email protected]
Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2020
S2
Table S1. The mechanical parameters of Cx samples.....................................................................S4
Table S2. The bulk and network parameters of Cx samples...........................................................S5
Table S3. The Simha-Boyer (SB) parameters of Cx samples .........................................................S6
Table S4. The WLF parameters of Cx samples ..............................................................................S7
Table S5. The relative parameters of isomerization energy of samples .........................................S8
Table S6. The shape memory parameters of Cx samples ...............................................................S9
Table S7. Shear strengths of the bonded sheet pairs using pre-Cx as adhesives after curing.......S10
Figure S1. The photos of (a) pre-cross-linked PMA (pre-Cx) and (b) the cross-linked PMA (Cx)
samples. .........................................................................................................................................S11
Figure S2. The stress-strain traces of Cx samples. .......................................................................S12
Figure S3. 1H NMR spectra of (a) pre-C6, (b) pre-C8, (c) pre-C10 and (d) pre-C12. .................S13
Figure S4. The carbon atom contents of Cx samples....................................................................S14
Figure S5. Master curves of dynamic storage moduli of Cx samples...........................................S15
Figure S6. Calculated values of (a) free volume fractions and (b) isomerization energies of Cx
samples against carbon numbers of used diol cross-linkers. .........................................................S16
Figure S7. Apparent activation energy (Ea) against Mc of Cx samples ........................................S17
Figure S8. (a) Optical pictures of the loaded substrate pairs bonded with Cx and the fracture
surfaces of different substrates after lap shear tests, and SEM images of fracture surfaces of (b)
iron based sheets and (c) PET sheets. ............................................................................................S18
Figure S9. (a) The stress-strain curves of combined Cx ribbons (30 mm×2 mm×1.5 mm) (Cx/Cx
compound joints) and the pictures of compound joints with different parts (b) before and (c) after
tensile tests.....................................................................................................................................S19
Figure S10. (a) Schematics of the points on the combined C6/C12 sample collected for the EDX
tests and (b) collected carbon atom contents of C6/C12 sample at different points......................S20
S3
Figure S11. (a) Responsive sensitivity and recovery rates of the Cx samples; (b) shape recovery
process of a Cx twisted ribbon and (c) infrared thermal images of twisted part of ribbon. ..........S21
Video S1. Bulk appearance and properties of pre-cross-linked PMA (pre-Cx)
Video S2. Shape-memory behavior of a ribbon sample with single component (C8) (95 oC)
Video S3. Shape-memory behavior of a ribbon sample composed of four parts with various spatial
distributions of networks (C6+C8+C10+C12) (95 oC)
Video S4. Fabricating a flower-like sample using four kinds of Cx samples (C6+C8+C10+C12)
Video S5. Fabricating robotic arms using pre-Cx as the joint connecting wires
Video S6. Programable (step-by-step) motions of a robotic arm driven by SME of Cx samples
Video S7. Shape recovery processes of Cx twisted ribbons
S4
Table S1. The mechanical parameters of Cx samples
samplesYoung's modulus
(MPa)
yield strength
(MPa)
elongation at break
(%)
C6 2079.95±233.12 73.44±6.37 7.16±0.95
C8 2027.04±165.78 63.81±5.61 7.69±0.86
C10 1636.95±98.18 49.71±3.79 8.73±0.75
C12 1416.98±62.37 43.46±2.64 11.15±0.12
S5
Table S2. The bulk and network parameters of Cx samples
samples gel content (%) ρ (kg m-3) Tg (K) E (MPa) a) ν (103mol m-3) Mc (g mol-1)
C6 97.6 1.09×103 359.55 12.27 1.231 885.29
C8 97.3 1.15×103 349.75 11.89 1.223 939.41
C10 97.4 1.22×103 341.65 11.58 1.216 1000.41
C12 97.4 1.29×103 336.15 11.51 1.227 1053.94
a) E is dynamic storage modulus at rubbery plateau.
Notes: the bulk densities of cross-linked samples increase with increased carbon numbers of diol
crosslinkers. All samples have almost the same gel contents. Therefore, the bulk density alteration
is nearly independent on the crosslinks in this work. Two possible reasons are proposed here. On
the one hand, the densities of diol molecules increase with increased carbon numbers (for instance,
1,6-hexanediol: 0.96×103 kg m-3, 1,8-octanediol: 1.05×103 kg m-3, and 1,10-decamethylenediol:
1.09×103 kg m-3). This leads to increase of densities of cross-linked system when using long-chain
diol as crosslinker. On the other hand, the reactive ability of diol reduces with increased aliphatic
chain length. This leads to the formation of ineffective crosslinks, indicating an increased amounts
of grafting chains. Those long side chains (grafted chains), to some extent, promote entanglements
of poly(L-malic acid) chains (currently it is hard to evaluate the critical entanglement molecular
weight of poly(L-malic acid), but the molecular weight of side chain of C12 samples is almost half
of that of poly(L-malic acid) oligomer), which has contribution to the increase of bulk densities,
also.
S6
Table S3. The Simha-Boyer (SB) parameters of Cx samples
samples Tg (K) G L free,exs,SB g/V V
C6 332.32 6.954×10-5 4.144×10-4 3.449×10-4 0.124
C8 326.76 7.898×10-5 5.041×10-4 4.251×10-4 0.139
C10 321.42 8.628×10-5 5.371×10-4 4.508×10-4 0.145
C12 308.77 9.247×10-5 5.967×10-4 5.042×10-4 0.156
S7
Table S4. The WLF parameters of Cx samples
samples b C1 fg (WLF)
C6 1 9.79144 0.04435
C8 1 7.97366 0.05446
C10 1 7.06198 0.06149
C12 1 6.52238 0.06657
S8
Table S5. The relative parameters of isomerization energy of samples
samples gT fg u ε u-ε
C6 0.124 0.04435 9.17798 5.40172 3.77626
C8 0.139 0.05446 8.29976 4.95420 3.34556
C10 0.145 0.06149 7.74149 4.74162 2.99987
C12 0.156 0.06657 7.37985 4.33405 3.04580
S9
Table S6. The shape memory parameters of Cx samples
samples fixing temp.
(Tfix)
recovery
temp.
(Trec)
shape fixity ratio
(Rf)
shape recovery
ratio
(Rr)
C6 35 oC 100 oC 95.8 % 97.2 %
C8 25 oC 90 oC 95.6 % 98.9 %
C10 15 oC 80 oC 95.7 % 99.8 %
C12 5 oC 70 oC 98.6 % 95.2 %
Notes: the samples show the shape fixity ratio (Rf) and the shape recovery ratio (Rr), which are
calculated according to:
(1)S1 S0f
S0, load S0
R
(2)S0, recover S0r
S1 S0
R
where the primary strain, the strain under load, temporary shape in the strain S0 S0, load S1
without load, and the strain after recovery. All samples present the Rf and Rr values S0, recover
higher than 95%.
S10
Table S7. Shear strengths of the bonded sheet pairs using pre-Cx as adhesives after curing a)
adhesives glass (MPa) iron (MPa) wood (MPa) polyester (MPa)
pre-C6 67.15±5.88 69.94±6.58 55.46±8.34 6.11±1.95
pre-C8 56.23±4.37 60.23±3.92 32.69±7.51 6.84±0.85
pre-C10 43.95±5.65 44.71±4.33 22.43±3.28 7.73±1.22
pre-C12 35.37±2.26 38.69±2.75 13.83±3.15 10.04±1.89
a) All sheet pairs were cured at 130 oC for 24 h under N2.
Note: The adhesion capacity of pre-Cx to the substrates reduces with weakened surface polarities
of those substrates, following the order of metal>glass>wood>plastics, and also depends on the
chain lengths of cross-linker diols in the pre-Cx system. For the substrates with stronger polarities
(glass, iron), shear strengths increase with decreased chain lengths of cross-linker diols because of
increased polarities of pre-Cx adhesives. Whereas for the plastics, shear strengths show opposite
trend, increasing with lengthened aliphatic chains of cross-linker diols, which is due to improved
interfacial compatibility between plastics and pre-Cx adhesive arising from decreased polarity of
pre-Cx. Details are discussed around Figure S7.
S11
Figure S1. The photos of (a) pre-cross-linked PMA (pre-Cx) and (b) the cross-linked PMA (Cx)
samples.
Note: pre-Cx sample behaves like transparent plasticine, shapeable and sticky, and hence can be
used as the glue/adhesive or the shaped semi-finished devices. After further crosslinking (also
called heat treatment or curing), transparent Cx sample is obtained. It has very good mechanical
strengths (43-73 MPa) and moduli (1.4-2.0 GPa), which depend on the chain lengths of diols
strongly (see Figure S2 & Table S2).
(a) (b)
S12
0.00 0.02 0.04 0.06 0.08 0.10 0.12
0
10
20
30
40
50
60
70
80
C6 C8 C10 C12
stre
ss(M
Pa)
strain
Figure S2. The stress-strain traces of Cx samples.
S13
6 5 4 3 2 1 0
dca'
ab e
3,42
51
ppm
in
tens
ity
6
O CH CH2 C O CH C
CO CH2
C
n m
O
O O
O
OH
O
OH
O CH CH2 C
O
CO
OH
O CH C
CH2
O
CO
OH
12
34
56
a' a
d
c b
e
pre-C6
6 5 4 3 2 1 0
pre-C8
inte
nsity
ppm
dca'ab e
3~6
27
18
OHC
H2C C O
HC C
CO CH2
C
n m
O
O O
O
O
OHC
H2C C
O
CO
OH
OHC C
CH2
O
CO
OH
OH
OH
12
34
56
78
e
a' a
d
c b
6 5 4 3 2 1 0
inte
nsity
ppm
pre-C10
dca'ab e
3~8
2
91
10
OHC
H2C C O
HC C
CO CH2
C
n m
O
O O
O
O
OHC
H2C C
O
CO
OH
OHC C
CH2
O
CO
OH
OH
OH
12
34
56
78
109
a' a
d
c b
e
6 5 4 3 2 1 0
inte
nsity
pre-C12
ppm
dca'ab e
3~102
11112
O CH CH2 C O CH C
CO CH2
C
n m
O
O O
O
O
O CH CH2 C
O
CO
OH
O CH C
CH2
O
CO
OH
OH
OH
12
34
56
78
109
1112
e
a' a
d
c b
Figure S3. 1H NMR spectra of (a) pre-C6, (b) pre-C8, (c) pre-C10 and (d) pre-C12.
Note: 1H NMR spectra of pre-Cx samples reveal new chemical shift (a' 4.44 ppm ppm) ascribed
to the methylene protons close to newly formed ester groups. The new shift at 4.03 ppm is also a
solid evidence of successful esterification between PMA backbone chain and diols.
(a) (b)
(c) (d)
S14
0.0
0.5
1.0
1.5
2.0
carb
on a
tom
con
tent
(%)
C12C10
C8
samples
C6
Figure S4. The carbon atom contents of Cx samples.
Note: The results were obtained by energy dispersive X-ray (EDX) spectrometric microanalysis
with a scanning electron microscopy (SEM, Zeiss-Supra55, Germany). It is clear that the carbon
atom contents of Cx samples increase with increase of chain lengths of diol crosslinkers.
S15
106107108109
1010
106107108109
1010
106107108109
1010
10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103106107108109
1010
frequency (Hz)
stor
age
mod
ulus
(Pa)
C6
C8
C10
C12
Figure S5. Master curves of dynamic storage moduli of Cx samples.
S16
6 8 10 120.00
0.04
0.08
0.12
0.16
0.20
carbon numbers of diols
f g (fr
ee v
olum
e fra
ctio
n)
WLF eq. SB eq.
(a)
6 8 10 12
2
4
6
8
10
carbon numbers of diols
ener
gy (k
J m
ol-1)
u u-
(b)
Figure S6. Calculated values of (a) free volume fractions and (b) isomerization energies of Cx
samples against carbon numbers of used diol cross-linkers.
S17
850 900 950 1000 1050 1100
180
210
240
270
300
E a (k
J m
ol-1)
Mc
Figure S7. Apparent activation energy (Ea) against Mc of Cx samples
Note: Arrhenius equation is used here to calculate apparent activation energy (Ea) of cross-linked
PMAs:
(3)aT
r
1 1- ln ( )EK T T
is shift factor, K is Boltzmann’s constant and Tr is reference temperature. is obtained by T T
TTS of dynamic modulus using 30 oC as Tr. Ea can then be calculated. It is clear that Ea reduces
with increased Mc. The difference of Ea implies a difference of temperature in a given relaxation
time, or a difference of relaxation time under a given temperature. 1, 2 Thus, C12 has rapider/easier
relaxations than C6 because the former possesses looser crosslinking networks and higher free
volume fraction relative to the latter.
(1) Zheng, N.; Hou, J. J.; Xu, Y.; Fang, Z. Z.; Zou, W. K.; Zhao, Q.; Xie, T. Catalyst-Free Thermoset
Polyurethane with Permanent Shape Reconfigurability and Highly Tunable Triple-Shape Memory
Performance. ACS Macro Lett. 2017, 6, 326-330.
(2) Ge, Q.; Luo, X. F.; Iversen, C. B.; Mather, P. T.; Dunna, M. L.; Qi, H. J. Mechanisms of triple-shape
polymeric composites due to dual thermal transitions. Soft Matter 2013, 9, 2212-2223.
S18
Figure S8. (a) Optical pictures of the loaded substrate pairs bonded with Cx and the fracture
surfaces of different substrates after lap shear tests, and SEM images of fracture surfaces of (b)
iron based sheets and (c) PET sheets.
Note: Pre-Cx can be used as adhesive to various substrates (metal, glass, wood, and plastics,
etc.). After curing, those substrate pairs bonded with Cx show good shear strengths, which is
strongly dependent on the polarities of substrates (Table S1 of SI). Cx has the best adhesion with
iron and glass, and as a result, the fracture surface is rather rough. The smoothest surface indicates
that the adhesion between Cx and plastics is the lowest, which is in consistent with shear strength
testing results. The adhesion capacity of pre-Cx to the substrates reduces with weakened surface
polarities of those substrates, following the order of metal>glass>wood>plastics, and also depends
on the chain lengths of cross-linker diols in the pre-Cx system. Therefore, one can determine
appropriate pre-Cx and substrate to prepare smart device according to the requirements of
applications.
(a)
(b) (c)
S19
0.00 0.02 0.04 0.06 0.08 0.10 0.120
10
20
30
40
50
60
70
80
strain
stre
ss (M
Pa)
C6/C8 C8/C10 C10/C12 C6/C12
(a)
Figure S9. (a) The stress-strain curves of combined Cx ribbons (30 mm×2 mm×1.5 mm) (Cx/Cx
compound joints) and the pictures of compound joints with different parts (b) before and (c) after
tensile tests.
Note: The yield strengths of a compound joint are ranged in between those of two bulks, close to
that of weaker one. For instance, the strength of C6/C8 joint is about 65 MPa (between 73 MPa of
C6 and 64 MPa of C8), and the strength of C6/C12 joint is about (between 73 MPa of C6 and 45
MPa of C12, Figure S2). This means that the two parts have a good connection at joint. As a
result, all joint samples show bulk fracture (see the arrow in Figure S9c), instead of interfacial one
after tensile tests.
interface interface(b) (c)
S20
0 10 20 30 40 50
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
car
bon
atom
con
tent
(%)
scanning position (mm)
transition region
C12
C6
(b)
Figure S10. (a) Schematics of the points on the combined C6/C12 sample collected for the EDX
tests and (b) collected carbon atom contents of C6/C12 sample at different points.
Note: EDX was used to detect interfacial thickness of a compound joint. Taking the combined
C6/C12 ribbon (~5.4 cm length) as an example, the carbon atom contents increased rapidly in the
joint region from C6 side to C12 one. However, the transition region is very narrow (~0.2-0.3 cm).
In the following shaping stage when the C6/C12 ribbon was used as a compound joint, the C6 part
experienced twisting and the C12 one experienced bending, which were independent with each
other. In this process, the jointed region might experience slight deformation, but its size was too
small to affect subsequent shape recovery of C6 or C12 part. Besides, C6 and C12 were used for
completing different actions, and those actions were asynchronous and mainly performed by the
main parts of C6 ribbon and C12 one, instead of the interfacial region (Figure 10a). Therefore, the
existence of interfacial layer (jointed region between C6 and C12) with good interfacial adhesion
(Figure S9) might not have evident influence on the C6/C12 compound joint to complete a whole
action step by step.
(a)
S21
0
5
10
15
20
25
resp
onsi
ve ti
me
(s)
recovery rate
C12C10C8C6samples
responsive time(a)
0.0
0.5
1.0
1.5
2.0
2.5
re
cove
ry ra
te (r
ad/s
)
Figure S11. (a) Responsive sensitivity and recovery rates of the Cx samples; (b) shape recovery
process of a Cx twisted ribbon and (c) infrared thermal images of twisted part of ribbon.
Note: The responsive sensitivity and recovery rate were evaluated roughly through the following
ways: the twisted ribbon connected with a U-shaped bar was place into a thermal environment,
starting timing, till the shape recovery completed. The time to the moment when the bar began its
rotation is defined as the responsive time. The average rate was defined as the time spent rotating
half a turn. All samples were pre-twisted with the same level, and rest for 1 day. The tests were
performed in a closed environment, ensuring stable heating. Details could be found in Video S7 of
SI.
(b)
(c)