Effect of the C/O ratio in Graphene Oxide Materials on the Reinforcement of Epoxy-Based
Nanocomposites
Cristina Vallés1*, Fabian Beckert2,3, Laura Burk2,3, Rolf Mülhaupt2,3, Robert J. Young1, Ian A. Kinloch1*
1
School of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
2
Institute for Macromolecular Chemistry, Albert-Ludwigs-University of Freiburg, Stefan-Meier-Straße
31, Freiburg, Germany
3
Freiburg Materials Research Center FMF, Stefan-Meier-Straße 21, Freiburg, Germany
Correspondence to: Cristina Vallés, Ian A. Kinloch (E-mail: cristina.valles@manchester.ac.uk,
ian.kinloch@manchester.ac.uk)
SUPPORTING INFORMATION
S1. X-ray photoelectron spectroscopy of GO and the TRGOs
X-ray photoelectron spectroscopy (XPS) was used to characterize the surface chemical structure and
composition of the graphene powders employed as reinforcement in the epoxy composites. The spectra
were collected using a Kratos Axis Ultra X-ray photoelectron spectrometer, equipped with an
aluminium/magnesium dual anode and a monochromated aluminium X-ray sources. The results
obtained are shown in Figure S1.
XPS survey (Figure S1a) reveals an increased C/O atomic ratio with increasing annealing temperatures.
For the starting GO material a C/O atomic ratio of 4.2 was observed, which was found to increase up to
9.22, 14.5 and 42.6 when the material was thermally reduced at 400, 750 and 1000 °C, respectively.
The high resolution C1s spectra (Figures S1a-d) revealed the presence of Csp2, C-O and C=O peaks at
284.5 eV, 286.74 and 288.19 eV, respectively, for the GO, whereas the Csp2 peak is the dominant peak
after thermal reduction1,2. The peak corresponding to C-O is drastically reduced after the thermal
treatment and the C=O peak disappeared for all the thermally-reduced materials.
1
(a)
TRGO-1000
CPS
TRGO-750
TRGO-400
GO
0
200
400
600
800
1000
1200
Binding Energy (eV)
Csp2
Csp2
(c) TRGO-400
C: 90.22 at.%
O: 9.78 at.%
C/O: 9.2
C-O
CPS
CPS
(b) GO
C: 80.78 at.%
O: 19.22 at.%
C/O: 4.2
C=O
C-O
294
292
290
288
286
284
282
294
292
Binding Energy (eV)
(d) TRGO-750
C: 93.56 at.%
O: 6.44 at.%
C/O: 14.5
290
288
286
284
282
284
282
Binding Energy (eV)
Csp2
(e) TRGO-1000
C: 97.71 at.%
O: 2.29 at.%
C/O: 42.6
CPS
CPS
Csp2
C-O
C-O
294
292
290
288
286
284
282
294
Binding Energy (eV)
292
290
288
286
Binding Energy (eV)
Figure S1. XPS survey (a) and high resolution C1s for the GO (b) and TRGO powders reduced at 400 °C
(c), 750 °C (d) and 1000 °C (e).
2
S2. SEM of GO and the TRGO materials
A Quanta 250 FEG (FEI, Hillsboro, OR, USA) scanning electron microscope was used to characterize the
morphology and size of the graphene powders studied as reinforcements. The pictures were taken in
high vacuum (10-3 Pa) with a LFD Detector using an accelerating voltage between 5 and 20kV.
SEM pictures showing the structure and size of the flakes of GO and the TRGO materials are shown in
Figure S2.
3
Figure S2. SEM pictures of the graphene powders: GO (a, b); TRGO-400 (c, d); TRGO-750 (e, f); TRGO1000 (g, h).
Although these images revealed that the diameter of the GO flakes decreased with the applied thermal
treatments, the observed diameters still remained quite big (≥ 50 µm) for the graphene oxide flakes
even after being treated at 1000 °C.
S3. Filler Orientation
The orientation of the GO and TRGO fillers was evaluated using polarized Raman spectroscopy as shown
in Figure S3. The data show a random orientation in all cases.
4
100
1.2
1.0
80
120
(a)
60
140
GO/epoxy - 1 wt.%
D band
laser in z direction
40
0.4
0.6
160
20
0.4
0
0.2
0.4
0.4
0.6
0.6
0.8
0.8
1.0
1.0
1.2
1.2
100
80
120
(c)
1.0
60
140
TRGO-400/epoxy- 1 wt.%
D band
laser paralel to z
40
0.8
160
20
0.2
0.0 180
0
0.2
0.4
0.6
0.8
1.0
1.2
100
1.2
80
120
(e)
1.0
0.4
160
20
140
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0
100
140
TRGO-400/epoxy - 1 wt.%
D band
laser paralel to x
40
160
20
180
0
80
TRGO-750/epoxy - 1 wt.%
60 D band
120
(f)
1.0
40
60
100
1.2
80
120
(d)
TRGO-750/epoxy - 1wt.%
D band
60 laser in z direction
0.8
0.6
40
0.0 180
0.2
0.4
140
0.2
0.0 180
0.6
GO/epoxy - 1 wt.%
D band
laser in x direction
60
0.8
0.2
1.2
80
120
(b)
1.0
0.8
0.6
100
1.2
laser in x direction
140
40
0.8
160
20
0.2
0.6
0.4
0.0 180
0
20
0.0 180
0.2
0.2
0.4
0.4
0.6
0.6
0.8
0.8
1.0
1.0
1.2
1.2
1.4
1.2 (g)
1.0
140
0.8
0.6
160
0.4
0.2
0.0 180
0.2
0.4
0.6
0.8
1.0
1.2
1.4
160
0.2
100
120
80
0
TRGO-1000/epoxy - 1 wt.%
60 D band
laser paralel to z
40
20
0
1.4
1.2 (h)
1.0
140
0.8
0.6
160
0.4
0.2
0.0 180
0.2
0.4
0.6
0.8
1.0
1.2
1.4
100
120
80
TRGO-1000/epoxy - 1 wt.%
60 D band
laser paralel to x
40
20
0
Figures S3. Variation of ID with the rotation of the specimen showing the random orientation of the (a,
b) GO, (c, d) TRGO-400 (e, f), TRGO-750 and (g, h) TRGO-1000 in the epoxy matrix in the 1 wt.% loaded
nanocomposites. A polarized Raman laser beam aligned either in the z- or in the x-direction to the
surface of the specimen with VV polarization was used. The curves are least squares fits to the
experimental points.
5
S4. Mechanical Properties
The mechanical property data for all the nanocomposite materials studied are summarized in Table S1.
Table S1. Mechanical property data obtained from the stress-strain curves in Figure 3.
GO/Epoxy (wt.%)
0
0.5
1
2
3
4
5
Young’s Modulus (GPa)
1.97  0.13
2.53  0.12
2.82  0.11
2.33  0.40
2.41  0.20
2.35  0.19
2.60  0.10
Fracture Stress (MPa)
49.30  2.85
51.08  4.00
49.41  9.38
33.50  4.80
33.60  4.30
36.04  10.40
41.40  7.00
Fracture Strain (%)
3.40  1.02
2.76  0.38
2.66  0.33
1.60  0.37
1.35  0.22
1.89  0.70
2.10  0.60
TRGO-400/Epoxy (wt.%)
0
0.5
1
2
3
4
5
Young’s Modulus (GPa)
1.97  0.13
2.52  0.40
2.70  0.20
2.35  0.23
2.10  0.20
2.40  0.30
1.90  0.01
Fracture Stress (MPa)
49.30  2.85
48.80  0.97
32.00  12.80
17.95  7.51
25.84  3.00
21.00  5.00
4.00  1.85
Fracture Strain (%)
3.40  1.02
2.64  0.507
1.39  0.90
0.41  0.50
1.35  0.24
0.90  0.40
0.17  0.11
TRGO-750/Epoxy (wt.%)
0
0.5
1
2
3
4
5
Young’s Modulus (GPa)
1.97  0.13
2.39  0.30
2.71  0.20
2.44  0.30
2.56  0. 01
2.68  0.12
2.89  0.40
Fracture Stress (MPa)
49.30  2.85
27.00  3.97
21.61  14.00
26.00  3.70
9.07  3.00
13.62  4.26
6.90  1.50
Fracture Strain (%)
3.40  1.02
1.21  0.44
0.93  0.73
1.08  0.02
0.29  0.05
0.60  0.16
0.43  0.16
TRGO-1000/Epoxy (wt.%)
0
0.5
1
2
3
4
5
Young’s Modulus (GPa)
1.97  0.13
2.50  0.12
2.52  0.20
2.60  0.21
1.94  0.01
2.00  0.20
2.38  0.32
Fracture Stress (MPa)
49.30  2.85
42.41  10.41
36.75  10.73
18.46  11.18
6.15  1.10
7.20  3.00
7.08  1.42
Fracture Strain (%)
3.40  1.02
2.08  0.69
1.87  1.07
0.77  0.63
0.24  0.08
0.47  0.20
0.57  0.23
6
S5. Rheological Behavior of the Nanocomposites
106
(a)
GO
(b)
102
G'
108
10-1
TRGO-400
107
102
10
G'
0
10
(e)
*(Pas)
104
108
G', G'' (Pa)
103
6
10-2 -1
10
G''
Epoxy
0.5 wt.%
1 wt.%
2 wt.%
3 wt.%
100
101
102
Frequency (rad/s)
TRGO-750
G'
100
108
10
(g)
G''
Epoxy
0.5 wt.%
1 wt.%
2 wt.%
3 wt.%
100
101
102
Frequency (rad/s)
TRGO-1000
104
102
100
10-2
G'
G''
Epoxy
0.5 wt.%
1 wt.%
2 wt.%
3 wt.%
(f)
Epoxy
0.5 wt.%
1 wt.%
2 wt.%
3 wt.%
100
101
Frequency (rad/s)
TRGO-750
102
Epoxy
0.5 wt.%
1 wt.%
2 wt.%
3 wt.%
103
(h)
100
101
Frequency (rad/s)
TRGO-1000
102
Epoxy
0.5 wt.%
1 wt.%
2 wt.%
3 wt.%
105
103
101 -1
10
100
102
Frequency (rad/s)
TRGO-400
105
107
6
100
101
Frequency (rad/s)
103
101 -1
10
103
Epoxy
0.5 wt.%
1 wt.%
2 wt.%
3 wt.%
4 wt.%
105
107
104
102
(d)
101 -1
10
103
6
10-2 -1
10
G', G'' (Pa)
100
101
102
Frequency (rad/s)
* (Pas)
G', G'' (Pa)
10
(c)
G''
Epoxy
0.5 wt.%
1 wt.%
2 wt.%
3 wt.%
4 wt.%
100
10-2 -1
10
* (Pas)
102
*(Pas)
G', G'' (Pa)
104
GO
100
101
Frequency (rad/s)
102
Figure S5. Dynamic frequency sweeps on the studied graphene oxide dispersions in the epoxy resin
conducted within the LVR (at a constant strain amplitude of 0.1%). Dependence of: G' and G'' (a) and η*
(b) of GO, G' and G'' (c) and η* (d) of TRGO-400, G' and G'' (e) and η* (f) of TRGO-750, G' and G'' (g) and
η* (h) of TRGO-1000 with the applied frequency.
7
10 (a)
GO
108
Epoxy
0.5 wt.%
1 wt.%
2 wt.%
3 wt.%
4 wt.%
(Pas)
101 -3
10
108
(c)
10-1
101
Shear Rate (s-1)
TRGO-750
10-1
101
Shear Rate (s-1)
(d)
10-1
101
Shear rate (s-1)
TRGO-1000
106
102
103
Epoxy
0.5 wt.%
1 wt.%
2 wt.%
3 wt.%
104
102
100 -3
10
103
Epoxy
0.5 wt.%
1 wt.%
2 wt.%
3 wt.%
4 wt.%
102
108
Epoxy
0.5 wt.%
1 wt.%
2 wt.%
3 wt.%
104
100 -3
10
TRGO-400
104
100 -3
10
103
 (Pas)
 (Pas)
106
(b)
106
 (Pas)
2
10-1
101
Shear Rate (s-1)
103
Figure S6. Steady shear rate flow behaviour of the GO (a), TRGO-400 (b), TRGO-750 (c) and TRGO-1000
(d) dispersions in the epoxy at different concentrations.
References
1. Rella, S.; Giuri, A.; Corcione, C. E.; Acocella, M. R.; Colella, S.; Guerra, G.; Listorti, A.; Rizzo, A.;
Malitesta, C. Vacuum 2015, 119, 159-162.
2. Vallés, C.; David Núñez, J.; Benito, A. M.; Maser, W. K. Carbon 2012, 50, 835-844.
8