Supplementary Material for Molecular Ordering of Organic Molten Salts Triggered by Single-Walled Carbon Nanotubes

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1 Supplementary Material for Molecular Ordering of Organic Molten Salts Triggered by Single-Walled Carbon Nanotubes Takanori Fukushima, * Atsuko Kosaka, Yoji Ishimura, Takashi Yamamoto, Toshikazu Takigawa, Noriyuki Ishii, and Takuzo Aida * Materials and Methods High-purity SWNTs (HiPco, > 95%) were obtained from Carbon Nanotechnologies Inc., and used throughout this work unless otherwise noted. Graphite (1 2 µm) and C 60 (99.9%) were purchased from Aldrich and TCI, respectively. EMIBF 4 was purchased from Aldrich and used as received. Other ionic liquids such as BMIBF 4 (S1), HMIBF 4 (S1), BMIPF 6 (S2), EMITf 2 N (S3), and BMITf 2 N (S3) were prepared according to literature methods, and unambiguously characterized. General procedure for gelation. SWNTs (2 mg) were suspended in a RIL (0.4 ml), and the mixture was ground with an agate mortar for 15 minutes, where the suspension gradually turned into a glossy, black paste. The resulting paste was centrifuged at 9,100g for 3 hours, followed by the removal of excess liquid, to isolate a gel phase. Synthesis of ABMIPF 6 as a polymerizable RIL. 4-Bromobutyl acrylate. To a dry CH 2 Cl 2 (50 ml) solution of a mixture of 4-bromo-1-butanol (8.45 g, 55.2 mmol) and acryloyl chloride (5.24 g, 57.9 mmol) was added Et 3 N (12.0 ml, 86.1 mmol) at 0 C under Ar, whereupon a precipitate formed. After stirred for 4 h at 0 C, the reaction mixture was filtered off from insoluble substances. The filtrate was diluted with CH 2 Cl 2, washed successively with water and brine, dried over MgSO 4, and then evaporated under reduced pressure at room temperature. The residue was subjected to vacuum distillation (1.1 Torr, C), to give 4-bromobutyl acrylate (6.28 g) as a colorless liquid in 55% yield. 1 H NMR (500 MHz, CDCl 3 ) δ = 6.41 (dd, J = 17.5, 1.5 Hz, 1H), 6.12 (dd, J = 17.5, 10.5 Hz, 1H), 5.84 (dd, J = 10.5, 1.5 Hz, 1H), 4.20 (t, J = 6.5 Hz, 2H), 3.45 (t, J = 6.5 Hz, 2H), (m, 2H), S1

2 (m, 2H). ABMIPF 6. A dry MeCN (28 ml) solution of a mixture of 1-methylimidazole (1.55 g, 18.9 mmol) and 4-bromobutyl acrylate (3.91 g, 18.9 mmol) was heated at 85 C under Ar. After 16 h, the reaction mixture was evaporated to dryness under reduced pressure at room temperature, and the residue was dissolved in deionized water (300 ml). To this solution was dropwise added an aqueous solution (40 ml) of KPF 6 (4.01 g, mmol) at 0 C, and the mixture was stirred at the same temperature. After 2.5 h, the reaction mixture was allowed to warm to room temperature, and extracted several times with CH 2 Cl 2. The combined extract was washed with water, dried over MgSO 4, and evaporated under reduced pressure at room temperature to give an oily residue, which was further dried at 70 C under reduced pressure for 24 h, to leave ABMIPF 6 (4.38 g) as a yellowish viscous liquid in 66% yield. 1 H NMR (500 MHz, DMSO) δ = 9.08 (s, 1H), 7.75 (dd, J = 1.5, 1.5 Hz, 1H), 7.68 (dd, J = 1.5, 1.5 Hz, 1H), 6.32 (dd, J = 17.5, 1.5 Hz, 1H), 6.16 (dd, J = 17.5, 10.5 Hz, 1H), 5.94 (dd, J = 10.5, 1.5 Hz, 1H), 4.19 (t, J = 7.5 Hz, 2H), 4.12 (t, J = 6.5 Hz, 2H), 3.83 (s, 3H), (m, 2H), (m, 2H); 13 C NMR (125 MHz, DMSO) δ = , , , , , , 63.29, 48.33, 35.71, 26.11, 24.81; IR (KBr) 3170, 2965, 1718, 1576, 1412, 1298, 1279, 1204, 1169, 841, 558 cm -1 ; MALDI- TOF-MS found m/z ([M] + calcd for C 11 H 17 O 2 N 2 : ). Synthesis of an ABMIPF 6 polymer and its composite with SWNTs. Polymerization of ABMIPF 6 in the absence of SWNTs. A Teflon vessel containing a mixture of ABMIPF 6 (1.51 g, 4.26 mmol) and 2,2 -azobisisobutyronitrile (AIBN, 10 mg, mmol) under Ar was heated at C, whereupon the polymerization of ABMIPF 6 took place to reach 93% conversion in 10 h, affording a transparent polymeric substance. 1 H NMR (500 MHz, DMSO) δ = 8.96 (s, 1H), 7.65 (s, 1H), 7.61 (s, 1H), 4.12 (br t, 2H), 3.91 (br, 2H), 3.83 (br s, 3H), 2.13 (br, 1H), 1.78 (br, 3H), 1.49 (br, 3H); IR (KBr) 3173, 2966, 1735, 1577, 1170, 839, 557 cm - 1. Polymerization of ABMIPF 6 in the presence of SWNTs. A mixture of ABMIPF 6 (2.56 g, 7.23 mmol) and SWNTs (102 mg) was ground in an agate mortar for 30 min, and AIBN (15 mg, mmol) was added to the resulting gel. The mixture was further ground for 1 min and placed in a Teflon vessel. A black gel, thus obtained, was heated at 75 C under Ar, whereupon the polymerization of ABMIPF 6 took place and reached 90% conversion in 10 h, affording an S2

3 ABMIPF 6 polymer/swnt composite as a black material. 1 H NMR (500 MHz, DMSO) δ = 8.96 (br s, 1H), 7.64 (br, 2H), 4.12 (br, 2H), 3.83 (br, 5H), 2.13 (br, 1H), 1.78 (br, 3H), 1.49 (br, 3H); IR (KBr) 3173, 2966, 1734, 1577, 1169, 842, 557 cm -1. S3

4 Supporting Figures Fig. S1. Pictures of a bucky gel of BMIBF 4. (A) Phase-separation behavior of the gel: 2 mg of SWNTs were ground with 0.2, 0.4, 0.6, 0.8, and 1.0 ml (left-to-right) of BMIBF 4 for 15 minutes, and the resulting black pastes were centrifuged. As the amount of BMIBF 4 was increased, the colorless upper phase separated was increased in volume, while the quantity of the black, lower phase (gel phase) remained almost unchanged. When the amount of BMIBF 4 in the starting suspension was smaller than 0.2 ml, no ionic liquid phase separated even upon prolonged centrifugation. (B) Softness/hardness of the gel: Extrusion of the gel from a syringe (1.0 ml) gave a string, which resisted its own weight without disruption for a long time. (C) Gel-to-solid transition: Due to the non-volatility of ionic liquids, bucky gels, in sharp contrast with ordinary organo- and hydrogels, were highly stable and retained their physical properties even under reduced pressure. However, the gels were immediately transformed into a powdery solid by loss of the entrapped ionic liquids when placed on a filter paper (left). The picture on the right hand side shows a gel of BMIBF 4 placed on a glass plate for comparison. A bucky gel phase ionic liquid phase B C S4

5 Fig. S2. DSC thermograms (second cooling and heating) of mixtures of SWNTs and BMITf 2 N at different concentrations of SWNTs (0.05, 0.1, 0.25, 0.5, and 1.0 wt %). The samples were prepared by grinding SWNTs in BMITf 2 N for 30 min. As shown in Fig. 3C, BMITf 2 N alone, on heating, displayed a very broad exothermic peak. When the concentration of SWNTs was increased, the exothermic peak became simpler and shifted to a lower temperature. When the system reached a critical gel (SWNTs; 0.5 wt %), the exothermic peak appeared as a single peak at 52 C. Upon further increase in concentration of SWNTs (e.g., 1.0 wt %), the exothermic peak became much sharper without any further shift. S5

6 Fig. S3. DSC thermograms (second cooling and heating). (A) A bucky gel of EMITf 2 N containing 0.5 wt % of SWNTs, isolated by centrifugation of a black paste prepared from 2 mg of SWNTs and 0.4 ml of EMITf 2 N. (B) EMITf 2 N alone. Heating and cooling rates, 10 C min -1. Fig. S4. XRD patterns at 40 C on cooling at a rate of 10 min -1. Scan rate, 2 min -1. (A) A bucky gel of EMITf 2 N containing 0.5 wt % of SWNTs, isolated by centrifugation of a black paste prepared from 2 mg of SWNTs and 0.4 ml of EMITf 2 N. (B) EMITf 2 N alone. EMITf 2 N alone showed broad and multiple exothermic and endothermic peaks with a glass transition at 94 C. In sharp contrast, in the presence of SWNTs, the system showed a pair of single exothermic ( 27 C, H = 17.2 kj mol -1 ) and endothermic ( 19 C, H = 19.1 kj mol -1 ) peaks due to crystallization and melting, respectively, without any glass transition. An essential difference was also observed for the XRD pattern of the bucky gel and EMITf 2 N alone. Furthermore, the diffraction peaks of EMITf 2 N, without SWNTs, were only very weak, indicating that the crystal growth is immature. These results clearly demonstrate that the SWNTs can induce molecular ordering of EMITf 2 N, similarly to the case of BMITf 2 N. S6

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8 Fig. S5. DSC thermograms (second cooling and heating). (A) A bucky gel of BMIPF 6 containing 0.5 wt % of SWNTs, isolated by centrifugation of a black paste prepared from 2 mg of SWNTs and 0.4 ml of BMIPF 6. (B) BMIPF 6 alone. Heating and cooling rates, 10 C min -1. Fig. S6. XRD patterns at 90 C on cooling and 20 C on heating at a rate of 10 min -1. Scan rate, 2 min -1. (A) A bucky gel of BMIPF 6 containing 0.5 wt % of SWNTs, isolated by centrifugation of a black paste prepared from 2 mg of SWNTs and 0.4 ml of BMIPF 6. (B) BMIPF 6 alone. Although the DSC profiles of the bucky gel and BMIPF 6 alone were similar to one another, the exothermic peak at 40 C, observed for BMIPF 6, was much sharper in the presence of SWNTs. On the other hand, the variable-temperature XRD profile of the bucky gel was clearly different from that of BMIPF 6 alone: On cooling, the bucky gel showed crystalline peaks at low temperatures such as 90 C, whereas BMIPF 6 alone showed only a broad peak. On heating, the bucky gel maintained such crystalline peaks until the beginning of the phase transition to a different crystalline form at 40 C, while BMIPF 6 alone remained amorphous until 40 C, where it started to crystallize. In a temperature range from 40 to 15 C, the bucky gel and BMIPF 6 alone both showed crystalline diffraction patterns, which however were essentially different from one another, as represented by XRD data at 20 C. From these observations, it is obvious that SWNTs affect the phase-transition behavior of BMIPF 6, similarly to the case of BMITf 2 N. S8

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10 Supporting References S1. J. D. Holbrey, K. R. Seddon, J. Chem. Soc., Dalton Trans (1999). S2. J. G. Huddleston, H. D. Willauer, R. P. Swatloski, A. E. Visser, R. D. Rogers, Chem. Commun (1998). S3. P. Bonhôte, A. P. Dias, N. Papageorgiou, K. Kalyanasundaram, M. Grätzel, Inorg. Chem. 35, 1168 (1996). S10