DOI: 10.1038/NCHEM.2315 Ultrahigh-throughput exfoliation of graphite into pristine single-layer graphene using microwaves and molecularly engineered ionic liquids Michio Matsumoto 1, Yusuke Saito 1, Chiyoung Park 1, Takanori Fukushima 2 and Takuzo Aida 1,3 * * To whom correspondence should be addressed. aida@macro.t-tokyo.ac.jp (T.A.) Table of Contents 1. General... S2 2. Synthesis and Characterization... S3 (Supplementary Figs. 1 14, Supplementary Table 1) 3. Effects of Microwaves... S14 (Supplementary Figs. 15 17) 4. Characterization of Graphene Sheets... S17 (Supplementary Figs. 18 23) 5. Intercalation of HF into Graphite... S23 (Supplementary Fig. 24) 6. Redispersion of Graphene Sheets in IL2PF 6... S24 (Supplementary Figs. 25 and 26) 7. Supplementary References... S25 NATURE CHEMISTRY www.nature.com/naturechemistry 1
1. General Unless otherwise noted, all reagents were purchased from Kanto Chemical, Aldrich, Tokyo Chemical Industry (TCI) and Wako Pure Chemical Industries, and used as received without further purification. Graphite supplied by Wako Pure Chemical Industries, Ltd was used after sieving with mesh #35. Microwave irradiation was performed with a CEM model Discover microwave reactor. 1 H and 13 C NMR spectra were recorded at 25 C on a JEOL model JEOL α-500 spectrometer, operating at 500 and 125 MHz, respectively, where chemical shifts (δ in ppm) were determined with respect to non-deuterated solvent residues as internal references. Electrospray ionization (ESI) mass spectrometry was performed on a Thermo Scientific model Exactive mass spectrometer. Transmission electron microscopy (TEM) and high-resolution TEM (HR-TEM) were carried out with JEOL model JEM-1400 and JEM-2100 electron microscopes operating at 120 kv, respectively. Samples were deposited on a specimen Cu grid covered with thin polymer and carbon support films manufactured by Okenshoji Co., Ltd. Tapping-mode atomic force microscopy (AFM) was performed in air at 25 C on a SII NanoTechnology model NanoNavi S-image (scan range: 20 20 µm) with silicon cantilevers (SI-DF20S, SII NanoTechnology). Scanning electron microscopy (SEM) images were collected with a JEOL model JSM-7001F scanning electron microscopy. Differential scanning calorimetry (DSC) was performed on a Mettler Toledo model DSC 822e differential scanning calorimeter, where the heating profile was recorded and analyzed using a Mettler Toledo STAR e software system. Electronica absorption and laser Raman spectra were recorded on a Molecular Devices SpectraMax Paradigm multi-mode microplate detection platform and a JASCO model NRS-5100 laser Raman spectrometer, respectively. Rheological properties were measured by using an Anton Paar model MCR-301 rheometer, with a 25-mm diameter parallel plate attached to a transducer. X-ray diffraction (XRD) measurements were carried out with a Rigaku model RINT-ULTIMA3 X-ray diffractometer. Small angle X-ray scattering (SAXS) was collected with a Rigaku model NANO-Viewer X-ray diffractometer using a Rigaku PILATUS 2D detector at a detection length of 120 cm. Surface tension measurements were carried out with a DataPhysics model OCA35 automatic video-based optical contact angle and drop contour analysis system. Electronic conductivity measurements were carried out with a Solartron model 1260 impedance/gain-phase analyzer. NATURE CHEMISTRY www.nature.com/naturechemistry 2
2. Synthesis and Characterization 2.1. Synthesis of IL2OTs, IL2PF 6 and IL2TFSI IL2OTs: To an MeCN solution (20 ml) of triethylene glycol bis(p-toluenesulfonate) (50.5 g, 0.110 mol) under Ar was added 1-butylimidazole (33.1 g, 0.266 mol), and the mixture was stirred for 16 h at 60 ºC. The reaction mixture was evaporated to dryness under reduced pressure, and to the viscous residue was added CH 2 Cl 2 (10 ml). The resulting solution was washed 3 times with AcOEt (50 ml). The lower phase separated was collected and evaporated by a rotary evaporator, and the residue was put overnight in a vacuum oven at 105 C over P 2 O 5, affording IL2OTs as pale yellow viscous liquid (74.9 g, 0.105 mol, 95%). 1 H NMR (500 MHz, DMSO-d 6, 25 ºC) δ (ppm) 9.16 (s, 2H), 7.79 (t, J = 1.8 Hz, 2H), 7.72 (t, J = 1.8 Hz, 2H), 7.47 (d, J = 8.0 Hz, 4H), 7.11 (d, J = 8.0 Hz, 4H), 4.32 (t, J = 5.0 Hz, 4H), 4.16 (t, J = 7.1 Hz, 4H), 3.72 (t, J = 4.9 Hz, 4H), 3.50 (s, 4H), 2.27 (s, 6H), 1.73 (tt, J = 7.3, 7.3 Hz, 4H), 1.21 (qt, J = 7.5, 7.5 Hz, 4H), 0.86 (t, J = 7.5 Hz, 6H); 13 C NMR (125 MHz, DMSO-d 6, 25 ºC) δ (ppm) 145.7, 137.6, 136.3, 128.0, 125.4, 122.8, 122.2, 69.3, 68.1, 48.7, 48.5, 31.3, 20.7, 18.7, 13.2; ESI-MS: m/z 535.2922 ([M OTs] +, calcd. for C 27 H 43 N 4 O 5 S + 535.2949). IL2PF 6 : To an MeCN/water (40 ml/80 ml) solution of IL2OTs (73.8 g, 0.104 mol), was added KPF 6 (43.2 g, 0.235 mol), and the mixture was stirred for 2 h at 25 ºC. The reaction mixture spontaneously separated into an aqueous phase and an organic phase as the reaction proceed, and was decanted to remove the upper aqueous phase. CH 2 Cl 2 (20 ml) was added to the organic phase collected, and the mixture was washed 3 times with distilled water (50 ml). The lower phase separated was collected and evaporated by a rotary evaporator, and the residue was put overnight in a vacuum oven at 105 C over P 2 O 5, affording IL2PF 6 as pale yellow viscous liquid (58.4 g, 0.0884 mol, 85%). 1 H NMR (500 MHz, DMSO-d 6, 25 ºC) δ (ppm) 9.09 (s, 2H), 7.75 (t, J = 1.8 Hz, 2H), 7.69 (t, J = 1.8 Hz, 2H), 4.32 (t, J = 5.0 Hz, 4H), 4.17 (t, J = 7.3 Hz, 4H), 3.74 (t, J = 4.8 Hz, 4H), 3.52 (s, 4H), 1.76 (tt, J = 7.5, 7.5 Hz, 4H), 1.24 (qt, J = 7.4, 7.4 Hz, 4H), 0.89 (t, J = 7.3 Hz, 6H); 13 C NMR (125 MHz, DMSO-d 6, 25 ºC) δ (ppm) 136.3, 122.8, 122.2, 69.4, 68.1, 48.8, 48.6, 31.4, 18.8, 13.2; ESI-MS: m/z 509.2453 ([M PF 6 ] +, calcd. for C 20 H 36 F 6 N 4 O 2 P + 509.2480). NATURE CHEMISTRY www.nature.com/naturechemistry 3
IL2TFSI: To an MeCN solution (20 ml) of IL2OTs (36.8 g, 0.052 mol) was added LiTFSI (35.0 g, 0.122 mol), and the mixture was stirred for 2 h at 25 ºC. The reaction mixture spontaneously separated into an aqueous phase and an organic phase as the reaction proceed, and was decanted to remove the upper aqueous phase. CH 2 Cl 2 (20 ml) was added to the organic phase, and the mixture was washed 3 times with distilled water (50 ml). The lower phase separated was collected and evaporated by a rotary evaporator, and the residue was put overnight in a vacuum oven at 105 C over P 2 O 5, affording IL2TFSI as pale yellow viscous liquid (44.5 g, 0.048 mol, 92%). 1 H NMR (500 MHz, DMSO-d 6, 25 ºC) δ (ppm) 9.13 (s, 2H), 7.78 (t, J = 1.8 Hz, 2H), 7.72 (t, J = 1.8 Hz, 2H), 4.34 (t, J = 4.8 Hz, 4H), 4.19 (t, J = 7.3 Hz, 4H), 3.76 (t, J = 5.0 Hz, 4H), 3.54 (s, 4H), 1.78 (tt, J = 7.5, 7.5 Hz, 4H), 1.24 (qt, J = 7.5, 7.5 Hz, 4H), 0.91 (t, J = 7.5 Hz, 6H); 13 C NMR (125 MHz, DMSO-d 6, 25 ºC) δ (ppm) 136.5, 123.5, 122.9, 122.4, 121.0, 118.4, 115.8, 69.6, 68.3, 49.0 48.8, 31.5, 18.9, 13.2; ESI-MS: m/z 644.1963 ([M TFSI] +, calcd. for C 22 H 36 F 6 N 5 O 6 S 2 + 644.2006). 2.2. Synthesis of IL1 and IL1PF 6 IL1 : 2-(2-(2-Methoxyethoxy)ethoxy)ethyl 4-methylbenzenesulfonate was synthesized according to ref. S1. IL1PF 6 : To an MeCN solution (10 ml) of IL1 (22.9 g, 0.072 mol) under Ar was added 1-butylimidazole (8.97 g, 0.072 mol), and the mixture was stirred at 60 ºC for 48 h. To the reaction mixture was added an aqueous solution (20 ml) of KPF 6 (15.17 g, 0.082 mol), and the mixture was stirred for 2 h at 25 ºC. The reaction mixture was extracted 3 times with CH 2 Cl 2 (30 ml), and the lower phase separated was collected and washed 3 times with distilled water (90 ml). The lower phase separated was collected and evaporated by a rotary evaporator, and the residue was put overnight in a vacuum oven at 105 C over P 2 O 5, affording IL1PF 6 as transparent liquid (28.3 g, 0.068 mol, 94%). 1 H NMR (500 MHz, DMSO-d 6, 25 ºC) δ (ppm) 9.10 (s, 1H), 7.77 (t, J = 1.8 Hz, 1H), 7.74 (t, J = 2.0 Hz, 1H), 4.33 (t, J = 4.8 Hz, 2H), 4.17 (t, J = 7.3 Hz, 2H), 3.76 (t, J = 5.3 Hz, 2H), 3.54 3.52 (m, 2H), 3.49 3.46 (m, 4H), 3.41 3.40 (m, 2H), 3.23 (s, 3H), 1.76 (tt, J = 7.5, 7.5 Hz, 2H), 1.24 (qt, J NATURE CHEMISTRY www.nature.com/naturechemistry 4
= 7.5, 7.5 Hz, 2H), 0.89 (t, J = 7.5 Hz, 3H); 13 C NMR (125 MHz, DMSO-d 6, 25 ºC) δ (ppm) 136.3, 122.8, 122.2, 71.3, 69.6, 69.5, 69.5, 68.0, 58.1, 48.8, 48.6, 31.4, 18.8, 13.2; ESI-MS: m/z 271.2009 ([M PF 6 ] +, calcd. for C 14 H 27 N 2 O 3 + 271.2017). 2.3. Synthesis of IL4, IL4, IL4OTs and IL4PF 6 IL4 : To an MeCN solution (60 ml) of triethylene glycol bis(p-toluenesulfonate) (52 g, 0.113 mol) under Ar was added 1-butylimidazole (4.69 g, 0.038 mol), and the mixture was stirred for 10 h at 60 ºC. The reaction mixture was evaporated to dryness under reduced pressure, and a CH 2 Cl 2 (15 ml) solution of the viscous residue was subjected to column chromatography on SiO 2 with CH 2 Cl 2 /MeOH = 9/1 as eluent, to allow isolation of IL4 as pale yellow viscous liquid (15 g, 0.026 mol, 68%). 1 H NMR (500 MHz, DMSO-d 6, 25 ºC) δ (ppm) 9.14 (s, 1H), 7.77 7.73 (m, 4H), 7.49 7.46 (m, 4H), 7.05 (d, J = 8.0 Hz, 2H), 4.32 (t, J = 4.9 Hz, 2H), 4.16 (t, J = 7.0 Hz, 2H), 4.08 (t, J = 4.6 Hz, 2H), 3.73 (t, J = 4.9 Hz, 2H), 3.54 3.42 (m, 6H), 3.36 (s, 4H), 2.41 (s, 3H), 2.27 (s, 3H), 1.75 (tt, J = 7.5, 7.5 Hz, 2H), 1.24 (qt, J = 7.4, 7.4 Hz, 2H), 0.87 (t, J = 7.5 Hz, 3H); 13 C NMR (125 MHz, DMSO-d 6, 25 ºC) δ (ppm) 145.8, 145.0, 137.6, 136.3, 132.3, 130.2, 128.1, 127.6, 125.5, 122.8, 122.2, 70.0, 69.5, 69.4, 68.1, 67.9, 48.8, 48.5, 31.3, 21.1, 20.8, 18.7, 13.3; ESI-MS: m/z 411.19 ([M OTs] +, calcd. for C 20 H 31 N 2 O 5 S + 411.20). IL4 : 1,1 -[1,2-Ethanediylbis(oxy-2,1-ethanediyl)]bis(imidazole) was synthesized according to ref. S2. IL4OTs: To an MeCN (10 ml) solution of a mixture of IL4 (13.85 g, 0.024 mol) and IL4 (2.97 g, 0.012 mol) was stirred under Ar for 48 h at 60 ºC. The reaction mixture was evaporated by a rotary evaporator, and the residue was put overnight in a vacuum oven at 105 C over P 2 O 5, affording IL4OTs as pale yellow viscous liquid (16.82 g, 0.012 mol, 100 %). 1 H NMR (500 MHz, DMSO-d 6, 25 ºC) δ (ppm) 9.17 (s, 2H), 9.14 (s, 2H), 7.79 7.73 (m, 6H,), 7.47 (d, J = 7.5 Hz, 8H), 7.11 (d, J = 7.5 Hz, 8H), 4.34 (m, 16H), 3.73 (t, NATURE CHEMISTRY www.nature.com/naturechemistry 5
J = 4.9 Hz, 12H), 3.51 (d, J = 1.2 Hz, 12H), 2.28 (s, 12H), 1.74 (tt, J = 7.5, 7.5 Hz, 4H), 1.22 (qt, J = 7.5, 7.5 Hz, 4H), 0.87 (t, J = 7.3 Hz, 6H); 13 C NMR (125 MHz, DMSO-d 6, 25 ºC) δ (ppm) 145.7, 137.7, 136.6, 136.3, 128.1, 125.5, 122.8, 122.6, 122.3, 69.3, 68.2, 68.1, 48.7, 48.5, 31.4, 20.8, 187, 13.3; ESI-MS: m/z 1243.5404 ([M OTs] +, calcd. for C 59 H 87 N 8 O 15 S 3 + 1243.5453). IL4PF 6 : To an MeCN solution (10 ml) of IL4OTs (16.82 g, 0.012 mol) was added an aqueous solution (20 ml) of KPF 6 (9.97 g, 0.054 mol), and the mixture was stirred for 2 h at 25 ºC. The reaction mixture spontaneously separated into an aqueous phase and an organic phase as the reaction proceed, and was decanted to remove the upper aqueous phase. The organic phase was washed 3 times with distilled water (90 ml). The lower phase separated was collected and evaporated by a rotary evaporator, and the residue was put overnight in a vacuum oven at 105 C over P 2 O 5, affording IL4PF 6 as yellow viscous liquid (14.78 g, 0.011 mol, 94%). 1 H NMR (500 MHz, DMSO-d 6, 25 ºC) δ (ppm) 9.11 (s, 2H), 9.06 (s, 2H), 7.78 (t, J = 1.5 Hz, 2H), 7.70 (d, J = 1.5 Hz, 6H,), 4.35 4.30 (m, 12H), 4.17 (t, J = 7.0 Hz, 4H), 3.73 (t, J = 4.5 Hz, 12H), 3.52 (t, J = 2.5 Hz, 12H), 1.77 (tt, J = 7.4, 7.4 Hz, 4H), 1.24 (qt, J = 7.5, 7.5 Hz, 4H), 0.89 (t, J = 7.3 Hz, 6H,); 13 C NMR (125 MHz, DMSO-d 6, 25 ºC) δ (ppm) 136.5, 136.24, 122.8, 122.6, 122.3, 69.3, 68.2, 68.1, 48.8, 48.6, 31.3, 18.7, 13.2; ESI-MS: m/z 1165.3973 ([M PF 6 ] +, calcd. for C 38 H 66 F 18 N 8 O 6 P + 3 1165.4031). NATURE CHEMISTRY www.nature.com/naturechemistry 6
2.4. 1 H and 13 C NMR Spectroscopy Supplementary Figure 1. 1 H NMR spectrum of IL2PF 6 in DMSO-d 6 at 25 ºC. Asterisked signals at δ2.49 and 3.34 ppm are due to partially non-deuterated residues of DMSO-d 6 and water, respectively. Supplementary Figure 2. 13 C NMR spectrum of IL2PF 6 in DMSO-d 6 at 25 ºC. An asterisked signal at δ39.5 ppm is due to DMSO-d 6. NATURE CHEMISTRY www.nature.com/naturechemistry 7
Supplementary Figure 3. 1 H NMR spectrum of IL2TFSI in DMSO-d 6 at 25 ºC. Asterisked signals at δ2.49 and 3.34 ppm are due to partially non-deuterated residues of DMSO-d 6 and water, respectively. Supplementary Figure 4. 13 C NMR spectrum of IL2TFSI in DMSO-d 6 at 25 ºC. An asterisked signal at δ39.5 ppm is due to DMSO-d 6. NATURE CHEMISTRY www.nature.com/naturechemistry 8
Supplementary Figure 5. 1 H NMR spectrum of IL1PF 6 in DMSO-d 6 at 25 ºC. Asterisked signals at δ2.49 and 3.34 ppm are due to partially non-deuterated residues of DMSO-d 6 and water, respectively. Supplementary Figure 6. 13 C NMR spectrum of IL1PF 6 in DMSO-d 6 at 25 ºC. An asterisked signal at δ39.5 ppm is due to DMSO-d 6. S9 NATURE CHEMISTRY www.nature.com/naturechemistry 9
Supplementary Figure 7. 1 H NMR spectrum of IL4PF 6 in DMSO-d 6 at 25 ºC. Asterisked signals at δ2.49 and 3.34 ppm are due to partially non-deuterated residue of DMSO-d 6 and water, respectively. Supplementary Figure 8. 13 C NMR spectrum of IL4PF 6 in DMSO-d 6 at 25 ºC. An asterisked signal at δ39.5 ppm is due to DMSO-d 6. NATURE CHEMISTRY www.nature.com/naturechemistry 10
2.5. Electrospray Ionization Mass (ESI-MS) Spectrometry Supplementary Figure 9. ESI-MS spectrum of IL2PF 6. Obsd. m/z 509.2453 ([M PF 6 ] +, calcd. for C 20 H 36 F 6 N 4 O 2 P + 509.2480). Supplementary Figure 10. ESI-MS spectrum of IL2TFSI. Obsd. m/z 644.1963 ([M TFSI] +, calcd. for C 22 H 36 F 6 N 5 O 6 S 2 + 644.2006). NATURE CHEMISTRY www.nature.com/naturechemistry 11
Supplementary Figure 11. ESI-MS spectrum of IL1PF 6. Obsd. m/z 271.2009 ([M PF 6 ] +, calcd. for C 14 H 27 N 2 O 3 + 271.2017). Supplementary Figure 12. ESI-MS spectrum of IL4PF 6. Obsd. m/z 1165.3973 ([M PF 6 ] +, calcd. for C 38 H 66 F 18 N 8 O 6 P 3 + 1165.4031). NATURE CHEMISTRY www.nature.com/naturechemistry 12
2.6. Surface Tensions of Ionic Liquids Supplementary Table 1. Surface tensions of ionic liquids at 25 ºC. Density (g cm 3 ) Surface Tension (mn m 1 ) BMIPF 6 43.52* IL1PF 6 1.3 41 IL2PF 6 1.4 43 IL4PF 6 IL2TFSI 1.4 1.4 38 33 * Data reported in ref. S3. 2.7. Differential Scanning Calorimetry (DSC) Analysis Supplementary Figure 13. DSC trace of IL2PF 6 on second heating (red) from 50 C and second cooling (black) from 150 C at a rate of 10 ºC min 1. NATURE CHEMISTRY www.nature.com/naturechemistry 13
2.8. X-ray Photoelectron Spectroscopy (XPS) Analysis Supplementary Figure 14. XPS spectrum of IL2PF 6 placed on an indium-foil sheet. 3. Effects of Microwaves 3.1. Heating Effect of Microwaves on Ionic Liquids Supplementary Figure 15. Temperature change profile of an IL2PF 6 suspension of graphite (25 mg/ml, 0.5 ml) upon 30-min exposure to microwaves at 30 W. NATURE CHEMISTRY www.nature.com/naturechemistry 14
3.2. Heating Effect of Microwaves on Decomposition of IL2PF 6 Supplementary Figure 16. 1 H NMR spectra in DMSO-d 6 at 25 ºC of IL2PF 6 (a) before and (b) after 30-min exposure to microwaves at 30 W. NATURE CHEMISTRY www.nature.com/naturechemistry 15
3.3. Heating Effect of Microwaves on Decomposition of IL2TFSI Supplementary Figure 17. 1 H NMR spectra in DMSO-d 6 at 25 ºC of IL2TFSI (a) before and (b) after 30-min exposure to microwaves at 30 W. NATURE CHEMISTRY www.nature.com/naturechemistry 16
4. Characterization of Graphene Sheets 4.1. Powder X-ray Diffraction (XRD) Analysis Supplementary Figure 18. (a, b) Powder XRD profiles of precursor graphite (a) and graphene sheets (b). The exfoliation and isolation conditions are essentially identical to those described in Fig. 1. NATURE CHEMISTRY www.nature.com/naturechemistry 17
4.2. Scanning Electron Microscopy (SEM) Analysis SEM a b c 1 µm 1 µm 2 µm d e f 10 µm 25 µm 25 µm Supplementary Figure 19. (a d) SEM micrographs of graphene sheets. The samples were prepared by casting from MeCN onto a silicon substrate. The exfoliation and isolation conditions are essentially identical to those described in Fig. 1. S18 NATURE CHEMISTRY www.nature.com/naturechemistry 18
4.3. Transmittance Electron Microscopy (TEM) Analysis Supplementary Figure 20. (a d) TEM and (e h) HR-TEM micrographs of graphene sheets. The samples were prepared by casting from MeCN onto a carbon-grid substrate. The exfoliation and isolation conditions are essentially identical to those described in Fig. 1. NATURE CHEMISTRY www.nature.com/naturechemistry 19
4.4. Atomic Force Microscopy (AFM) Analysis Supplementary Figure 21. Tapping-mode AFM images of graphene sheets. The sample was prepared by casting from MeCN onto a mica substrate. The exfoliation and isolation conditions are essentially identical to those described in Fig. 1. NATURE CHEMISTRY www.nature.com/naturechemistry 20
4.5. Electronic Conductivity Analysis Supplementary Figure 22. (a, b) Schematic illustrations of a micro-gap electrode for electronic characterization, (c) optical micrograph and (d) I V profile of a graphene sheet on the micro-gap electrode (R S : an average of those obtained with four separately prepared micro-gap electrode devices). 4.5.1. Methods Micro-gap Au electrodes with a gap of ~2 µm were fabricated on silicon substrates. Samples were prepared by casting an MeCN dispersion of graphene sheets onto the micro-gap electrodes. Conditions for the exfoliation of graphite and isolation of the resultant graphene sheets were essentially identical to those described in Fig. 1. Four separately prepared micro-gap electrode devices were used for the I V profile evaluation of a single graphene sheet with a two-point probe method in conjunction with a Solartron model 1260 impedance/gain-phase analyzer. From the resultant I V profiles, resistance values R at 0.2 V were obtained and converted into sheet resistance values R S using the equation R S = RW/L, where W and L represent graphene sheet width and electrode gap length, respectively. NATURE CHEMISTRY www.nature.com/naturechemistry 21
4.6. XPS Analysis Supplementary Figure 23. (a) C1s and (b) N1s XPS spectra of precursor graphite, IL2PF 6 and isolated graphene sheets. NATURE CHEMISTRY www.nature.com/naturechemistry 22
5. Intercalation of HF into Graphite Supplementary Figure 24. (a c) Time-dependent XRD profiles in 0 (a), 12 (b), and 36 hours (c) of graphite immersed at 25 C in HF-containing IL2TFSI (for preparation, see the Method section). The diffractions at 2θ = 26.5º and 15.4º are due to the interlayer distances of graphite without and with intercalated HF, respectively, while a broad peak centered at 2θ = 20.0º is due to an amorphous halo of IL2TFSI. NATURE CHEMISTRY www.nature.com/naturechemistry 23
6. Redispersion of Graphene Sheets in IL2PF 6 6.1. Electronic Absorption Spectroscopy Supplementary Figure 25. Electronic absorption spectrum of graphene sheets redispersed in IL2PF 6 (1.0 mg/ml). The exfoliation and isolation conditions are essentially identical to those described in Fig. 1. 6.2. Dynamic Viscoelastic Analysis Supplementary Figure 26. (a) Strain (γ) dependencies of storage moduli (G, solid circles) and loss moduli (G, open circles) of IL2PF 6 containing graphene sheets (25 mg/ml, blue), together with those of its reference samples; graphite in IL2PF 6 (25 mg/ml, grey) and IL2PF 6 alone (orange) at 35 ºC. The applied angular frequency (ω) was 0.628 rad s 1. The S24 NATURE CHEMISTRY www.nature.com/naturechemistry 24
γ sweep was made from lower to higher. (b) Storage moduli (G, solid circles) and loss moduli (G, open circles) of IL2PF 6 containing graphene sheets (25 mg/ml) at different temperatures. Applied γ and ω were 0.1% and 0.628 rad s 1, respectively. The exfoliation and isolation conditions are essentially identical to those described in Fig. 1. 7. Supplementary References S1. Gooding, J. J. et al., J. Am. Chem. Soc. 134, 844 (2012). S2. Bara, J. E. Ind. Eng. Chem. Res. 50, 13614 (2011). S3. Countinho, J. A. P. et al., J. Colloid Interface Sci. 314, 621 (2007). NATURE CHEMISTRY www.nature.com/naturechemistry 25