Supplemental Information
Poly(methacrylic acid)-grafted clay-thermoplastic elastomer composites with waterinduced shape-memory effects
Tongfei Wu,†, ‡ Kevin O’kelly‡ and Biqiong Chen†,*
†
Department of Mechanical and Manufacturing Engineering, Trinity College Dublin, Dublin,
2, Ireland.
14
20
TPU
TPU4
TPU8
TPU16
TPU32
10
(a)
8
6
4
(b)
TPU
TPU4
TPU8
TPU16
TPU32
16
Swelling degree (% w/w)
12
Swelling degree (% w/w)
12
8
4
2
0
0
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
Time (h)
Time (h)
70
(c)
TPU
TPU4
TPU8
TPU16
TPU32
60
Swelling degree (% w/w)
‡
Department of Materials Science and Engineering, University of Sheffield, Sheffield, S1
3JD, UK.
50
40
30
20
10
0
0
1
2
3
4
5
6
7
Time (h)
Figure S1. Typical swelling behaviors of TPU and PMAA-g-clay-TPU composite films as a
function of immersion time in distilled water (a), 0.1 M HCl (b) and 0.1 M NaOH (c).
1
16
never wetted
0.1 M NaOH
0.1 M HCl
distilled water
14
12
E' (MPa)
10
8
6
4
2
0
0
5
10
15
20
25
PMAA-grafted clay (vol.%)
Figure S2. Storage moduli of PMAA-g-clay-TPU composite films dried from the wet
samples showing the moduli return to the original high values.
3.5
3.5
(a)
TPU4
TPU8
TPU16
TPU32
3.0
2.5
Stress (MPa)
2.5
Stress (MPa)
(b)
TPU4
TPU8
TPU16
TPU32
3.0
2.0
1.5
2.0
1.5
1.0
1.0
0.5
0.5
u
0
0
10
20
30
40
50
60
70
80
0
90
0
100
10
20
30
40
Strain (%)
50
60
70
80
90
100
Strain (%)
1.8
(c)
TPU4
TPU8
TPU16
TPU32
1.6
1.4
Stress (MPa)
1.2
1.0
0.8
0.6
0.4
0.2
0
0
10
20
30
40
50
60
70
80
90
100
Strain (%)
Figure S3. Tensile stress-strain curves for the first cyclic tests before shape recovery.
Before testing, the samples were immersed in distilled water (a), 0.1 M HCl (b) and 0.1 M
NaOH (c) for 1 h.
2
Modelling Section
l
t
d
PMAA
clay platelet
SCHEME S1 Schematic illustration of intercalated PMAA-g-claytactoids.
To apply the models, the following parameters are measured and/or calculated. E' of
PMAA-g-clay particles is calculated according to Eq. (3 and 4). Because of the high content
of clay in PMAA-g-clay and the removal of excess PMAA during synthesis, PMAA-g-clay
particles are considered as intercalated tactoids (Scheme S1) in accordance with the XRD
results. van Es et al. suggested a shape factor of ξ = 2l/3t to be used in Eq. (3, 4) for
polymer-clay nanocomposites.1 l and t refer to the length and thickness of clay platelets,
respectively. The average l for Cloisite® Na+ was 72 nm2 and t was 0.98 nm3. The effective
volume fraction of clay layers (Φclay) in the intercalated PMAA-g-clay tactoids is calculated
according to Eq. (S1)4:
𝛷𝑐𝑙𝑎𝑦 =
𝑛𝑡
𝑑(𝑛−1)+𝑡
(S1)
Here n refers the number of platelets in a tactoid and d is the interlayer spacing, which is
1.6 nm determined from XRD. As shown in SEM, the particle size is over 50 nm, so n > 31.
Thus, Eq. (8) can be reduced to Φclay ≈ t/d = 0.98/1.6 = 0.61. So, the volume fraction of the
intercalating polymer in the tactoid is 0.39, which is lower than that calculated from the
weight percentages and the densities of the bulk polymer and the clay (~0.77), meaning
that the gallery spacing of the clay is occupied by the tightly packed polymer. Young’s
modulus of clay platelets is considered as 226 GPa5-6, and PMAA modulus as 0.79 GPa7. So,
Young’s modulus of PMAA-g-clay particles is calculated as 44 GPa using Eq. (3, 4).
Due to the particle size of the PMAA-g-clay (Fig. 3) and the XRD results, the PMAA-g-clayTPU composites are considered as ‘conventional’ polymer-clay composites. So, in the
calculations of the moduli for PMAA-g-clay-TPU composites, ξ is taken as 2 for the HalpinTsai model for polymer composites filled with spherical particles.8 Ef in the Halpin-Tsai
model refers to Young’s modulus of PMAA-g-clay particles, while Ef refers to Young’s
modulus of PMAA-g-clay film for the percolation model9 which was measured as 0.10 GPa.
Φc was considered as 2.5 vol.% based on the results of the swelling tests.
References
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7
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9
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