modified graphene nanocomposites with near infrared responsive shape memory and healing properties

Accepted Manuscript Macromolecular nanotechnology Supramolecular hydrogen-bonded polyolefin elastomer/modified graphene nanocomposites with near infrared responsive shape memory and healing properties Muhammad Kashif, Young-Wook Chang PII: DOI: Reference:

S0014-3057(15)00082-8 http://dx.doi.org/10.1016/j.eurpolymj.2015.02.007 EPJ 6754

To appear in:

European Polymer Journal

Received Date: Revised Date: Accepted Date:

14 November 2014 29 January 2015 5 February 2015

Please cite this article as: Kashif, M., Chang, Y-W., Supramolecular hydrogen-bonded polyolefin elastomer/ modified graphene nanocomposites with near infrared responsive shape memory and healing properties, European Polymer Journal (2015), doi: http://dx.doi.org/10.1016/j.eurpolymj.2015.02.007

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Supramolecular hydrogen-bonded polyolefin elastomer/modified graphene nanocomposites with near infrared responsive shape memory and healing properties Muhammad Kashif, Young-Wook Chang* Polymer Nano Materials Laboratory, Department of Chemical Engineering, Hanyang University, Ansan, Gyeonggi 426-791, Republic of Korea *corresponding author: [email protected]

Abstract Small amounts (0.25-1 wt%) of octadecylamine modified graphene oxide (ODA-GO) were incorporated into a 3-amio-1,2,4-triazole (ATA) crosslinked maleated polyethylene-octene elastomer (ATA-POE), a structurally dynamic supramolecular hydrogen-bonded thermoplastic elastomer, via melt blending to prepare ATA-POE/ODA-GO nanocomposites. Field-emission scanning electron microscopy and X-ray diffraction analysis for the ATA-POE/ODA-GO composites revealed that the ODA-GO sheets were dispersed at the nanoscale level in the elastomer matrix which results in enhancement of the mechanical properties of the nanocomposites at low filler loadings. These nanocomposites exhibit both shape memory and scratch-healing effects under near infrared (NIR) light exposure. It was revealed from the results that ODA-GO acted as NIR-triggered nanoheaters as well as reinforcing filler for the elastomer matrix. Keywords: supramolecular hydrogen-bonded elastomer; graphene; infrared light response; shape memory effect; healing effect

1. Introduction Recently, graphene has emerged as a promising polymer nanofiller due to its unique structural, mechanical, thermal, and electro-optical properties. [1-4] Specifically, the aromatic carbon network structures of the graphene endows its nanocomposites to have high thermal conductivity [5, 6] and infrared (IR) light response (i.e., the photothermal effect). [7] Such unique features of graphene have been utilized to prepare several light responsive polymer/graphene nanocomposites. [8-10] Feng and coworkers [8] dispersed sulfonated reduced graphene oxide/sulfonated carbon nanotube hybrids in a polyurethane matrix to prepare IRtriggered actuators based on shape recovery. Kim and Park [9] prepared crystalline polyurethane/graphene chemical hybrids and reported near infrared (NIR)-actuated shape memory effects in the hybrid. Kim and coworkers [10] reported optically-healable polyurethane/graphene nanocomposites exhibit healing property due to a photothermal effect induced by phenyl isocyanate-modified graphene under NIR light exposure. Self-healing polymers (SHPs) can repair damage (scratches, cracks) on the application of a stimulus, and provide extended application lifetime and reduced maintenance cost. [11, 12] One approach to prepare SHPs is the use of dynamic interactions, which may be supramolecular (hydrogen bonding, ionic interactions, π-π stacking, metal-ligand coordination) or dynamic covalent bonds. [13] These structurally dynamic polymers show rearrangement in their structure in response to a stimulus. The healing process in polymers is externally stimulated by heat [14, 15], water [16] or light [17]. Though there are many known stimuli for SHPs, light has the unique advantage of remote triggering and the ease of switching on-off for actuation. [18, 19] Weder and coworkers [18] reported ultraviolet (UV) light healable supramolecular nanocomposites based on poly (ethylene-co-butylene)/ureido pyrimidone (UPy)-modified

cellulose nanocrystals. Rowan and coworkers [19] synthesized a covalently crosslinked polymer containing a disulfide network that exhibits photohealing under UV light. Such self-healing effects can be manifested in some shape memory polymers (SMPs), materials that have the ability to recover their permanent shape from temporary deformed shape on application of various stimuli such as temperature [20], light [7, 8] or water [21]. According to the reverse plasticity shape memory effect (RP-SME), SMPs can be deformed and fixed at room temperature while the original shape can be regained at high temperature. Such an effect is the basis of self-healing in SMPs. [22] Zhao and coworkers [23] have suggested that a photoresponsive nanofiller can be utilized to develop a polymer nanocomposite that shows both photoenabled shape memory and self-healing properties in the same nanocomposite matrix. Recently, Zhang and Zhao [24] reported that a chemically crosslinked poly (ethylene oxide)/functionalized gold nanoparticle composite exhibits both shape memory and healing properties due to a photothermal effect induced by gold nanoparticles under laser exposure. Xia and coworkers [25] crosslinked intrinsic shape memory poly(butyl acrylate-co-methyl methacrylate) bearing 2,6ʹ

bis(1 -methylbenzimidazolyl)prydine ligand with zinc salt to prepare metallosupramolecular polymer which showed both shape memory and healing properties under thermal heating or UV irradiation. To the best of our knowledge, there have been no prior reports of polymers that show both shape memory and healing properties under NIR light exposure. In our previous work [26], we showed that a supramolecular hydrogen-bonded polyolefin elastomer (ATA-POE), a thermoplastic elastomer prepared by crosslinking of semicrystalline maleated polyethylene-octene elastomer (mPOE) with 3-amino-1,2,4-triazole (ATA), displayed shape memory as well as healing effects upon thermal stimulation. In this study, we report that the ATA-POE/octadecylamine modified graphene oxide nanocomposites show both shape

memory and healing effects under NIR irradiation along with enhanced mechanical properties of the elastomer matrix. 2. Experimental 2.1. Materials Semicrystalline mPOE (Amplify GR 216) possessing a high maleic anhydride grafted level (>0.5 wt%) was purchased from the Dow Chemical Co. Midland, MI, USA. ATA was purchased from Tokyo Kasei Kogyo Co. Ltd, Japan. Graphite powder (type 282863, 20 μm particle size) and octadecylamine (99%) was purchased from Aldrich, South Korea. Concentrated sulfuric acid (95-98%), concentrated hydrochloric acid (36.5%) and potassium permanganate were supplied from Daejung Chemicals and Metals Co. Ltd, South Korea. Tetrahydrofuran (THF, 99.5%) and ethanol (99.7%) were purchased from Samchun Pure Chemical Co. Ltd, South Korea. 2.2. Preparation of ODA-GO Graphene oxide (GO) was prepared according to the modified Hummer’s method [27]. The modification and reduction of GO with ODA was done in our laboratory according to a previously reported method. [4] Briefly, GO was dissolved and exfoliated in 300 ml deionized water via an ultrasonication method. The solution of ODA (0.9 g) in 90 ml ethanol was prepared and transferred to a three neck flask along with the GO suspension. The mixture was stirred and refluxed for 20 h at 90 ˚C. The powder obtained was filtered and rinsed with 100 ml ethanol. The rinsing and filtration process was repeated 4 times to eliminate physically adsorbed ODA. Finally, the mixture was dried in an oven at 80 ˚C for 24 h to yield octadecylamine modified graphene oxide (ODA-GO). Thermogravimetric analysis (TGA) indicated weight loss of ~40%

in the temperature range 160 ˚C to 500 ˚C. Based on this observation, the amount of ODA present on the GO is about 40%. [4] 2.3. Preparation of ATA-POE/ODA-GO nanocomposites mPOE was melted in a Haake mixer for 2 min followed by the addition of ATA (1 phr) and mixing continued for 3 min at 180 ˚C and 60 rpm to form ATA-POE composite. Without dumping the above composite, ODA-GO was added and mixed for an additional 10 min to form ATA-POE/ODA-GO nanocomposites. The amounts of ODA-GO added to the ATA-POE composite were 0.25, 0.50, 0.75 and 1.00 wt%. The above nanocomposite samples were then pressed as sheets in an electrically-heated hydraulic press at 180 ˚C for 10 min and then slowly cooled to room temperature for further 10 min. 2.4. Characterizations Fourier transform infrared (FT-IR) spectra of pure GO and ODA-GO was recorded by Thermo Fisher Scientific Nicolet 6700, equipped with an attenuated total reflectance (ATR) accessory to evaluate the possible interaction between the GO and ODA. GO and ODA-GO were mixed with KBr powder and pressed into a thin pellet for FT-IR study. X-ray photoelectron spectroscopy (XPS) of GO and ODA-GO was recorded by using a VG Escalab electron spectrometer equipped with an Mg Kα X-ray source (1253.6 eV). A survey spectra and high resolution survey (C 1s) was performed for the GO and ODA-GO. X-ray diffraction (XRD) patterns of GO, ODA-GO and ATA-POE/ODA-GO nanocomposites were recorded by an X-ray diffractometer (D/MAX 2500/PC, Rigaku Corporation) with a Cu Kα radiation (λ= 1.54 ˚A) source at a generator voltage of 40 kV and 100 mA current. The experiment was performed at a scan rate of 2˚/min over a scan range from 2˚ to 50˚.

The dispersion of ODA-GO in the ATA-POE matrix was characterized by field-emission SEM (JEOL JSM-630F) operating at an accelerating voltage of 15 kV. Tensile properties of the ATA-POE and ATA-POE/ODA-GO nanocomposites were measured by using a Shimadzu universal testing machine (AGS-500NX) at a strain rate of 500 mm/min, according to ASTM D412 specifications. Scratched and healed samples also followed the same specifications. Five dog-bone-shaped samples were used for the characterization of each sample. For near infrared triggered shape memory and healing effects, a 150 watt Philips infrared lamp was used. Samples were placed at a distance of 30 cm from the infrared lamp. The power density delivered to the sample was ~65 mW/cm2, as measured by a light intensity meter. The surface temperature of the NIR exposed sample was measured with the help of SUMMIT SDT25 (Digital thermometer). The shape fixity (F) and shape recovery (R) ratios of the samples were determined by the following equations; [28, 29] (1) (2)

Where Li denotes the initial length before starting the experiment, Lu denotes stretched length under load, Ls denotes stretched length without load, and Lr denotes recovered length after NIR exposure. 3. RESULTS AND DISCUSSION 3.1. Characterization of GO and ODA-GO 3.1.1. FT-IR analysis

Fig.1 shows FT-IR spectra of the GO and ODA-GO. The GO spectrum shows characteristic peaks of oxygen containing functionalities at 1724 cm-1 (carboxyl), 1032 cm-1 (epoxy) and a wide peak from 3000-3500 cm-1 which can be assigned to a hydroxyl group. The ODA-GO spectrum showed successful reduction and modification of GO by ODA. All of the peaks belonging to oxygen-containing functional groups were either diminished (i.e., 1724 cm-1) or reduced in intensity (i.e., 1032 cm-1, 1365 cm-1) in the ODA-GO spectrum, which provides evidence for the reduction of GO. Furthermore, the appearance of new peaks at 2918 cm-1 and _

2848 cm-1 correspond to CH2 asymmetric and symmetric stretching vibrations along with the 720 cm-1 peak (rocking vibration) implying the grafting of the octadecyl chain on the GO. [30] ….. Fig. 1….. 3.1.2. XPS analysis XPS analysis was performed to further confirm the modification of GO with ODA. ODAGO spectrum [Fig. 2(a)] shows that the binding energy signals of O 1s significantly decreased, implying a reduction of GO while the appearance of new binding energy signals (N 1s), and an increase in the intensity of the C 1s peak suggests grafting of ODA on GO. High resolution XPS spectrum of GO [Fig. 2(b)] indicate that a carbon atom is present in four different chemical environments: the graphite carbon skeleton (285 eV), hydroxyl groups (286.6 eV), the huge peak of epoxide groups (287.2 eV) and carboxyl groups (289.4 eV). The modification of GO with ODA [Fig. 2 (c)] shows that the huge peak area of the epoxide group was significantly reduced and not even a carboxyl group peak was observed. Moreover, a new peak was observed at 285.4 eV corresponding to C_N due to the interaction of ODA with GO. [31] ….. Fig. 2…..

The atomic concentration of each element (C 1s, N 1s and O 1s) was determined for GO and ODA-GO from XPS analysis. The elemental analysis of GO showed that it contained 59.5% carbon and 40.4% oxygen. After modification of GO with ODA, carbon content increased to 89.4% and oxygen content decreased significantly to 7.8%. Additionally, the nitrogen content was raised to 2.8%, implying successful grafting of the ODA chain on the GO. 3.2. Characterization of ATA-POE/ODA-GO nanocomposites 3.2.1. XRD and SEM analysis Fig. 3 shows the XRD patterns of GO, ODA-GO and ATA-POE/ODA-GO nanocomposites. The XRD pattern of GO [Fig. 3(a)] shows a sharp reflection at 2θ = 10.1˚ corresponding to an interlayer spacing of d = 0.91 nm. After simultaneous modification and reduction of GO with the ODA, the interlayer spacing of the GO increased to d = 2.2 nm (2θ = 4.1˚), as shown in Fig. 3(b). The ODA-GO spectra also shows a broad peak centered at 2θ = 21.1˚, which is attributed to the intercalation of long octadecylamine chains between the stacked graphene sheets. [32, 33] ….. Fig. 3….. The ATA-POE spectrum shows only one broad peak centered at 2θ = 19.2˚. The ATAPOE/ODA-GO nanocomposites also show only one peak at 2θ = 19.2˚ corresponding to ATAPOE and the absence of the ODA-GO peak, which suggests nanoscale dispersion of the ODAGO in the ATA-POE matrix. The dispersion of ODA-GO in the ATA-POE matrix was further analyzed by SEM analysis. Fig. 4 shows the cryogenically fractured surfaces of the ATA-POE/ODA-GO nanocomposites with varying amounts of ODA-GO. The micrographs indicate that most of the

ODA-GO sheets were fully exfoliated and well dispersed in the ATA-POE matrix. This is attributed to the good compatibility between octadecylamine chains of the ODA-GO and ATAPOE matrix. [4, 34] ….. Fig. 4….. The micrographs also reveal that the ODA-GO sheets were randomly distributed in the matrix. The bright (white) color shows the ODA-GO sheets (mostly rectangular in shape) coming out of the matrix during cryogenic fracture while the remaining part of the sheets were embedded in the matrix due to superior compatibility. At higher concentrations of ODA-GO (i.e., 0.75 and 1.00 wt %), some agglomeration was also observed, as shown in Fig. 4(c & d). 3.2.2. Tensile properties Fig. 5 shows the tensile properties of the ATA-POE/ODA-GO nanocomposites with various amounts of ODA-GO and the results are summarized in Table 1. The ATA-POE/ODAGO nanocomposites show higher tensile strength and modulus compared to the ATA-POE matrix. Additionally, tensile strength and modulus had an increasing trend with an increase in the amount of ODA-GO in the ATA-POE matrix with a small decrease in elongation at break. For instance, the incorporation of only 1.00 wt% of ODA-GO in the matrix resulted in an increase of the tensile strength from 9.13 MPa to 11.44 MPa, and 100% tensile modulus increased from 2.28 MPa to 2.70 MPa, as shown in Table 1. The enhancement of the mechanical properties is attributed to nanoscale dispersion of the ODA-GO in the ATA-POE matrix, which improved interfacial adhesion (hydrogen bonding interactions) between the modified graphene and supramolecular hydrogen-bonded (ATA-POE) elastomer. [31] Morimune et al. [35] also reported

an increase in the tensile strength and the modulus of the poly(vinyl alcohol)/graphene oxide nanocomposites due to hydrogen bonding interactions. ….. Fig. 5….. It can be seen from Table 1 that the tensile modulus (100%, 300%) of the graphene nanocomposites is not improved with the addition of more than 0.50 wt% of modified graphene. It is attributed to the agglomeration of graphene sheets in the nanocomposites as shown in Fig. 4(c & d). So, the 0.50 wt% of modified graphene is considered to be an appropriate amount for these nanocomposites. ….. Table 1….. 3.2.3. Shape memory effect NIR-triggered shape memory effects of the ATA-POE/ODA-GO nanocomposites are demonstrated in Fig. 6 and the quantitative results are tabulated in Table 2. All of the samples were stretched to 250% after heating them at 65 ˚C for 20 min and this temporary shape was kept at low temperatures to fix the deformed shape. Shape fixity and shape recovery ratios were calculated according to the equations (1) and (2), respectively. Upon exposure to NIR light, the graphene-based nanocomposites recovered their original shape due to the photothermal effect induced by graphene sheets. The ATA-POE exhibited only 1% recovery, while nanocomposite containing 1.00 wt% ODA-GO demonstrated shape recovery of almost 100%, as mentioned in Table 2. The results reveal that ODA-GO sheets worked as photothermal nanoheaters, converting infrared light to thermal energy. [7, 8] This thermal energy was transferred to the elastomer matrix to release the temporarily stored strain energy. Nanoscale dispersion of the ODA-GO in

the elastomer matrix might have resulted in an efficient photothermal effect, actuating the shape recovery process. [7, 9] ….. Fig. 6….. It was also observed that the nanocomposites containing 0.50-1.00 wt% ODA-GO recovered their original shape within 3 min, while the nanocomposite containing 0.25 wt% ODA-GO recovered its shape in 8 min. This faster recovery rate was attributed to an enhanced photothermal effect due to the higher amount of graphene in the nanocomposites; 0.50 wt% of modified graphene was considered to be an appropriate graphene concentration for these nanocomposites. ….. Table 2….. Further, we investigated the locally triggering of shape recovery under NIR exposure, as shown in Fig. 7. The rectangular sample (30 mm length) containing 0.50 wt% of ODA-GO was stretched to 100% (60 mm length) after heating at 65˚C for 20 min and kept at low temperature to fix the temporary elongated shape. The NIR light was exposed, successively, to three distinct segments (A, B and C) of the deformed elongated sample, as described in Fig. 7(b). One segment was exposed selectively to NIR light while the other two segments were covered with aluminium foil (as a reflector of NIR light). The procedure was adopted gradually for three segments (from left to right) to check the locally triggering of shape recovery. It can be seen from Fig. 7(c-e) that only an NIR exposed segment undergoes shape recovery due to the local photothermal effect. [24] ….. Fig. 7…..

3.2.4. Healing effect An NIR-triggered healing effect

was observed for the ATA-POE/ODA-GO

nanocomposites, as presented in Fig. 8. All of the samples were scratched to a depth of 60-70% with a razor blade. The scratch width for the ATA-POE sample is shown in Fig. 8(a); a similar scratch was made for the other nanocomposite samples. On exposure to NIR light, the infrared transparent ATA-POE sample does not show any healing effect even for 60 min, while all the graphene-based nanocomposites show healing on exposure to NIR light. Healing in the graphene-based nanocomposites is attributed to the photothermal effect, as discussed in the previous section. We have already documented healing effect in the supramolecular hydrogenbonded elastomer (mPOE crosslinked with ATA) under thermal stimulation in the previous articles. [15, 26] In the present work, nanoscale dispersion of the modified graphene (ODA-GO) in the supramolecular hydrogen-bonded polyolefin elastomer (ATA-POE) makes it possible to achieve the photo (NIR)-triggered healing effect. Due to the photothermal effect, [7, 36] heat energy is transferred to the elastomer matrix to melt the POE crystals, re-arrangement of the supramolecular hydrogen-bonded structure, and interfacial chain diffusion and re-entanglements across the scratched surfaces. [10, 17] ….. Fig. 8….. Fig. 9 shows the surface temperature rise of the APG-0.50 sample during NIR exposure. It can be seen that the surface temperature of the sample raised sharply from room temperature of 20 ˚C to 30 ˚C within 1 min exposure. The surface temperature of the sample stabilized at 47-48 ˚C after 30 min NIR exposure. ….. Fig. 9…..

The healing efficiency is calculated based on the recovery of the elongation at break (strain). Fig. 10(a) shows stress-strain curves of the scratched samples (APG-0.50) healed at various times under NIR irradiation. Strain recovers with increasing NIR exposure time. No significant healing was observed beyond 60 min. Thus, all of the samples were exposed to NIR light for 60 min to calculate the healing efficiency and reported in Table 2. Modified graphenebased nanocomposites containing 0.50 wt% graphene showed maximum healing efficiency of 45%. The decrease in healing efficiency beyond 0.50 wt% graphene is attributed to the agglomeration of graphene. ….. Fig. 10….. We also compared the scratch-healing effect of the NIR-healed samples with the thermally-healed samples for the nanocomposite containing 0.50 wt% ODA-GO. Fig. 10(b) shows that the strain of the sample was significantly reduced to 60 % after being scratched. Thermal healing was achieved by exposure of the scratched samples in a convection oven for 60 min at 90 ˚C. NIR irradiation of the scratched samples for 60 min produced sufficient heat to recover a strain of 395% as compared to the thermally-healed samples, which showed a strain recovery of 490%. The healing efficiency based on elongation at break indicates that NIR-healed samples recover 45%, while the thermally-healed sample shows recovery of 55%, as compared to unscratched samples. [25] These results indicate that scratched samples can also be healed effectively under NIR irradiation. 4. Conclusions Supramolecular polyolefin elastomer/modified graphene-based nanocomposites that demonstrated both NIR-actuated shape memory as well as healing effect, were prepared. Graphene oxide was modified and reduced with octadecylamine to act as NIR-actuated

nanoheaters and reinforcing filler for the elastomer matrix. FT-IR and XPS analysis revealed successful grafting of octadecylamine chains on the GO surface. SEM analysis showed nanoscale dispersion of the ODA-GO in the elastomer matrix, which was attributed to good compatibility between the octadecylamine chains and the elastomer matrix. Hydrogen bonding interactions (interfacial adhesion) between the supramolecular hydrogen-bonded elastomer and ODA-GO also resulted in an increase of the tensile strength of the nanocomposites at low graphene loadings. Nanocomposites containing graphene 0.50-1.00 wt% recovered their original shape within 3 min with a shape recovery ratio of ~100% under NIR exposure. Additionally, on exposure to NIR light, graphene-based nanocomposites containing 0.50 wt% loading showed a healing efficiency of 45%. These unique optically-triggered supramolecular hydrogen-bonded graphene-based nanocomposites with shape memory and healing properties may have potential applications in the automotive and coating industries, and can act as a functional thermoplastic elastomer. Acknowledgements Higher Education Commission of Pakistan is highly acknowledged for providing research funding (PhD) to Muhammad Kashif. This work was also supported by the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy, Republic of Korea.

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Figure captions Fig. 1. FT-IR spectra of the GO and ODA-GO Fig. 2. (a) Survey spectra of GO and ODA-GO and, C 1s deconvulated spectra of (b) GO and (c) ODA-GO Fig. 3. XRD patterns of (a) GO (b) ODA-GO and nanocomposites of ATA-POE with (c) 0 (d) 0.25 (e) 0.50 (f) 0.75 and (g) 1.00 wt% of ODA-GO Fig. 4. SEM micrographs of the cryogenically fractured surfaces of the ATA-POE/ODA-GO nanocomposites with (a) 0.25 (b) 0.50 (c) 0.75 and (d) 1.00 wt % of ODA-GO Fig. 5. Stress-strain curves of the ATA-POE/ODA-GO nanocomposites with different weight contents of ODA-GO Fig. 6. NIR-triggered shape memory process for the ATA-POE/ODA-GO nanocomposites with different weight content of ODA-GO loadings Fig. 7. NIR-controlled shape recovery of the APG-0.50 nanocomposite (a) original shape (b) 100% elongated shape and gradually three-step recovered shapes (c) left segment (d) middle segment and (e) right segment Fig. 8. SEM micrographs of (a) scratched sample width and healed samples (b) APG-0.25 (c) APG-0.50 (d) APG-0.75 (e) APG-1.00 Fig. 9. Temperature rise of the APG-0.50 sample under NIR irradiation for 60 min Fig. 10. Stress-strain curves of the APG-0.50 scratched samples (a) healed for various times under NIR irradiation and (b) comparison of NIR and thermal healed sample for 60 min

Tables list Table 1. Tensile properties of the ATA-POE/ODA-GO nanocomposites Table 2. Shape memory properties and healing efficiencies of NIR-triggered ATA-POE/ODA-GO nanocomposites

Fig. 1. FT-IR spectra of the GO and ODA-GO

Fig. 2. (a) Survey spectra of GO and ODA-GO and, C 1s deconvulated spectra of (b) GO and (c) ODA-GO

Fig. 3. XRD patterns of (a) GO (b) ODA-GO and nanocomposites of ATA-POE with (c) 0 (d) 0.25 (e) 0.50 (f) 0.75 and (g) 1.00 wt% of ODA-GO

Fig. 4. SEM micrographs of the cryogenically fractured surfaces of the ATA-POE/ ODA-GO nanocomposites with (a) 0.25 (b) 0.50 (c) 0.75 and (d) 1.00 wt % of ODA-GO

Fig. 5. Stress-strain curves of the ATA-POE/ODA-GO nanocomposites with different weight contents of ODA-GO

Fig. 6. NIR-triggered shape memory process for the ATA-POE/ODA-GO nanocomposites with different weight content of ODA-GO loadings

Fig. 7. NIR-controlled shape recovery of the APG-0.50 nanocomposite (a) original shape (b) 100% elongated shape and gradually three-step recovered shapes (c) left segment (d) middle segment and (e) right segment

Fig. 8. SEM micrographs of (a) scratched sample width and healed samples (b) APG0.25 (c) APG-0.50 (d) APG-0.75 (e) APG-1.00

Fig. 9. Temperature rise of the APG-0.50 sample under NIR irradiation for 60 min

Fig. 10. Stress-strain curves of the APG-0.50 scratched samples (a) healed for various times under NIR irradiation and (b) comparison of NIR and thermal healed sample for 60 min

Table 1. Tensile properties of the ATA-POE/ODA-GO nanocomposites Sample

ODA-GO (wt%)

σb

100% tensile 300% tensile 600% tensile modulus modulus modulus (Mpa) (Mpa) (Mpa)

Ɛb

(Mpa)

(%)

ATA-POE

0

2.28

3.42

5.13

9.13 ± 0.49

933 ± 10

APG-0.25

0.25

2.51

3.72

5.47

10.21 ± 0.45

932 ± 30

APG-0.50

0.50

2.65

4.01

6.10

10.74 ± 0.26

898 ± 10

APG-0.75

0.75

2.68

4.02

6.20

10.92 ± 0.18

889 ± 8

APG-1.00

1.00

2.70

4.12

6.43

11.44 ± 0.26

890 ± 11

σb= tensile strength, Ɛb= elongation at break

Table 2. Shape memory properties and healing efficiencies of NIR-triggered ATA-POE/ODA-GO nanocomposites

Sample

a

Shape Recovery ratio Healing efficiency a (%) (%) 0 1.1

ATA-POE

Shape fixity ratio (%) 86.2

APG-0.25

87.7

92.2

30 ± 8

APG-0.50

88.7

96.0

45 ± 6

APG-0.75

91.0

98.5

34 ± 5

APG-1.00

91.2

99.6

33 ± 4

Healing efficiency is calculated based on the recovery in elongation at break after NIR-irradiation for 60 min

Graphical Abstract

Highlights  Supramolecular hydrogen-bonded polyolefin elastomer/modified graphene nanocomposites were prepared via melt blending.  Octadecylamine modified graphene sheets were dispersed at the nanoscale level in the elastomer matrix.  Octadecylamine modified graphene acted as NIR-triggered nanoheaters as well as reinforcing filler for the elastomer matrix.  Nanocomposites exhibit both shape memory and healing properties under NIR light exposure.  Healing efficiency of the NIR-healed samples and thermally-healed samples are comparable.