Supplementary Data for“Structure-reinforcement correlation and chain dynamics in

graphene oxide and Laponite dispersed epoxy nanocomposites”

Devesh K. Chouhan1, Sangram K. Rath2, Arvind Kumar3, P.S. Alegaonkar3, Sanjay Kumar4, G. Harikrishnan4, T. Umasankar Patro1*

1Department of Materials Engineering, Defence Institute of Advanced Technology (DU), Girinagar, Pune-411025, Maharashtra, India

2Polymer Division, Naval Materials Research Laboratory (NMRL), DRDO, Ambernath, Thane-421506, Maharashtra, India

3Department of Applied Physics, Defence Institute of Advanced Technology (DU), Girinagar, Pune-411025, Maharashtra, India

4Department of Chemical Engineering, Indian Institute of Technology Kharagpur-721302, West Bengal, India

*Corresponding author: umasankarp@diat.ac.in, uma.patro@gmail.com

Wide-angle X-ray diffraction studies

Wide-angle X-ray diffraction (WAXD) was carried out on an X-ray diffractometer (Bruker

D5, Germany) at voltage and current of 40 kV and 40 mA, respectively, using a Cu-Kα X-ray

source of wavelength 0.154 nm. The patterns were recorded between 2θ = 7 and 60º, at a scan

rate of 0.4°/s. Figure S1 presents the WAXD pattern for graphite powder and graphene oxide

(GO), prepared by modified Hummers’ method. The graphite powder showed a peak at 26.5o,

which corresponds to the (002) plane of graphite and an interlayer-spacing of 0.34 nm [1].

However, GO showed a peak at ~11.8o, with an interlayer spacing (d002) of 0.74 nm,

indicating a significant changes in the layered structure.

Fig. S1: WAXD patterns of Graphite powder and Graphene oxide

Fourier transform infrared (FTIR) studies

FTIR studies were carried out between 400 and 4000 cm-1 using a Perkin-Elmer spectrometer

(FTIR 1605). Figure S2 shows the FTIR spectra of graphite powder and GO. Graphite shows

an IR band at ~1685 cm-1, corresponds to C-C stretching. The following characteristic IR

bands can be observed in the GO spectra. The broad band at 3410cm -1 is attributed to –OH

stretching. The peaks at ~1621cm-1 and ~1415cm-1 correspond to the –C=C stretching, –OH

bending, respectively. The broad band at 1062cm-1 is attributed to C-O-C stretching vibration.

From the FTIR results, it is evident that the functional groups like; epoxide, carboxyl and

hydroxyl groups are attached to the graphitic backbone resulting in formation of GO. The

formation of GO is supported by WAXD as discussed earlier.

Fig. S2: FTIR spectra of Graphite powder (a) and GO (b)

Raman spectroscopy studies

Raman spectra were recorded with a wavelength 633 nm using Horiba Labram-HR

spectrometer in which objective was fixed at 4X with a 325 nm notch filter. Figure S3

presents the Raman spectrum of GO. As seen in the figure, the G band, related to the first-

order scattering of tangential stretching (E2g) mode is obtained at ~1586 cm-1, whereas the D

band, which originates from disorder in the sp2–hybridized carbon atoms is seen at ~1327

cm-1, indicating the formation of sp3 domains due to the extensive oxidation [2]. The intensity

ratio of the D and G peaks is used as a parameter for determining degree of disorderness in

graphene. The various disorders in graphene include ripples, edges, charged impurities and

presence of domain boundaries etc [3]. That intensity ratio in GO is found to be ~1.32.

Fig. S3: Raman Spectra of GO

TGA Analysis

Thermo-gravimetric analysis (TGA) was performed on a Perkin–Elmer (USA) thermo-

gravimetric analyzer in nitrogen atmosphere. About 4 mg of sample was heated from room

temperature to 800 °C at a heating rate of 10°C/min. Figure S4 presents the weight loss vs.

temperature of GO. It can be observed from the figure that there is a weight loss below

100°C, which is mainly due to the elimination of moisture or water present in GO. A sharp

and significant mass loss (~20%) between 150 and 250°C is due to the decomposition of

labile oxygen functional groups; such as, epoxide and hydroxyl groups. The steady mass loss

observed between 250 and 800°C is due to the combustion of the residual char with a yield of

~ 36% obtained at 800°C.

Fig. S4: Wight loss vs. temperature of GO

Nanocomposite Preparation

Fig. S5: Schematic representation of nanocomposite preparation

Wide-angle X-ray diffraction

Fig. S6: WAXD patterns of GO (top), Laponite (bottom) nanocomposites and of neat epoxy,

the black colored patterns in both figures for comparison

Fig. S7: Representative tensile curves of epoxy and epoxy nanocomposites with (a) 0.1wt

%, (b) 0.3wt%, (c) 0.5wt% and (d) 1wt% of different nanofillers.

Fig. S8: Load vs. displacement curves obtained by three-point bend testing using single-

edge-notch bend (SENB) specimens of (a) GO and (b) Laponite nanocomposites.

Fig. S9: Typical FESEM fracture images of 0.1wt% GO composite. The length and

width of GO in composites are found to be ~4 (±2.9) µm, ~2.4 (±1.9) µm, respectively.

Fig. S10: Loss modulus (Eʹʹ) vs. tempereture curves of (a) GO and (b) Laponite composites

with different filler concentration, obtained from dynamic mechanical analysis. The heating

rate was 3°C/min.

Fig. S11: Tan δ as a function of temperature for various composites and epoxy obtained from

DMA. The experiments were performed at a heating rate of 3ºC/min. The curves are fitted

with Gaussian function.

Figure S12. Tan δ as a function of temperature for various composites and epoxy obtained

from DMA. The experiments were performed at a heating rate of 1ºC/min to confirm the

transitions due to bimodal distribution in nanocomposites. The curves are fitted with

Gaussian function.

Table S1: The peak values, which correspond to Tg obtained from Gaussian fitted DMA curves (Figs. S11 and S12)

% GO in nanocompositesHeating rate: 1°C/min Heating rate: 3°C/minTg1 Tg2 Tg1 Tg2

0 88 860.1 80 88 81 890.3 79 87 84 940.5 79 86 78 871.0 73 82 77 84

% Laponite in nanocomposites0.1 82 91 85 950.3 73 84 79 890.5 73 83 82 --1.0 78 91 82 93

Fig. 12 presents the fractography of nanocomposites. Fig. S12a and Fig. S12b (the magnified

image of Fig. S12a) are typical fractographs of GO composites, where GO agglomerate can

be clearly observed in the path of crack propagation. Fig. S12c presents the representative

fractograph of Laponite composite, in which the circled area seems to be an agglomeration of

Laponite particles. However, crack deflection as seen in case of GO could not be observed

through FESEM likely due to smaller size of Laponite particles than GO.

Fig. S12: Typical FESEM images of fracture surfaces of SENB specimens: (a-b) 1wt % GO,

(c) 1 wt% Laponite composite

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