Noncovalent Functionalization of Boron Nitride. Nanotubes Using Water-Soluble Synthetic Polymers. and the Subsequent Preparation of Superhydrophobic

Transcription

1 Supplementary Information Noncovalent Functionalization of Boron Nitride Nanotubes Using Water-Soluble Synthetic Polymers and the Subsequent Preparation of Superhydrophobic Surfaces Zhenghong Gao, Kei Fujioka, Toshiki Sawada, Chunyi Zhi, # Yoshio Bando, # Dmitri Golberg, # Mamoru Aizawa and Takeshi Serizawa *, Department of Advanced Interdisciplinary Studies, The University of Tokyo, Komaba, Meguro-ku, Tokyo , Japan. Department of Applied Chemistry, Meiji University, Higashi-mita, Tama-ku, Kawasaki, Kanagawa , Japan. Department of Organic and Polymeric Materials, Tokyo Institute of Technology, H121 Ookayama, Meguro-ku, Tokyo , Japan. # International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki , Japan. * To whom correspondence should be addressed to serizawa@polymer.titech.ac.jp. 1

2 Experimental Section Materials. Multi-walled BNNTs were synthesized by a carbon-free chemical vapor deposition method. 1 As-prepared BNNTs have a well-defined structure. The majority of BNNTs has the diameters from several nm to 60 nm, the sidewall numbers of around 40, and the length up to 10 µm. All polymers used in this study were purchased from Adrich-Sigma. All reagents were used as received without further purification. Preparation of Polymer-Functionalized BNNTs. In a typical experiment, 1 mg of BNNTs was added into an aqueous solution containing 1 mg ml -1 polymer in a total volume of 3 ml, and then the mixture was sonicated by a Branson Advanced Sonifier Model 250AA (output power: 20 W) for 1.5 h with a water cooling system, followed by the centrifugation at 2000 rpm for 25 min to remove any insoluble materials. The resultant dispersion was then stored at room temperature for further characterizations. For purification to remove free polymers, polymer-functionalized BNNTs were precipitated from dispersion by using centrifugation at rpm for 25 min, and then the precipitates were redispersed in 1 ml of milli-q and centrifuged again at the same conditions as above-mentioned. This redispersion-centrifugation cycle was repeated for at least 3 times to remove any free polymers, and finally the products were collected as a solid, which could be easily redispersed in water. The original BNNT sample was similarly prepared using the same procedure without polymers. Immobilization of Proteins onto Polymer-Functionalized BNNTs. To immobilize proteins onto the (-)PPP-functionalized BNNTs surface, BNNTs were firstly functionalized by (-)PPP, and then purified. In a typical experiment, 40 µl of purified (-)PPP-functionalized BNNTs dispersion was dropped on a clean silicon wafer, followed by complete drying under ambient atmosphere. Then, to remove any free (-)PPP, 100 µl of milli-q were dropped on that Si wafer. After incubation for 5 min, all of milli-q was removed by absorption with a filter paper. The processes were generally repeated over 4-6 times. Continuously, 40 µl of 200 µg ml -1 protein solutions of BSA in Britton Robinson buffer with ph 3, which was lower than the isoelectric point of BSA, were drop-cast on 2

3 the top of the sample prepared along the aforementioned method, followed by incubation at room temperature for 2 h for full interaction (the surface of the sample was still covered with the solution after incubation). Then, any free BSA species were washed away from the sample surface. After drying at room temperature, the samples were examined by AFM. Control experiments using only (- )PPP-functionalized BNNTs were in parallel performed to confirm the fact of protein immobilization. Preparation of Polymer-Functionalized BNNTs Coating. Silicon wafers were sonicated in milli-q water for 15 min, followed by washing with milli-q for complete cleaning. 600 µl of the dispersion of PXT-functionalized BNNTs was dropped on the surface of silicon wafers run by run in a pace of 200 µl. In each run, the surface was completely dried prior to the following run. After dropping all dispersions, the coating was thoroughly dried at the room environment. The final density of PXT-functionalized BNNTs was evaluated to be around 0.05 mg cm 2. Thermal Treatment of Polymer-Functionalized BNNTs Coating. The coating prepared along the aforementioned processes was used for thermal annealing conversion. The annealing was performed at 240 C for 6 h in a vacuum oven (Yamato, ADP200). Characterizations. AFM images were obtained with a SPM-9600 (Shimadzu) in a tapping mode using standard silicon cantilevers. For observing polymer-functionalized BNNTs, AFM samples were prepared by spin-coating 10 µl of the resultant dispersion at 600 rpm on a freshly cleaved mica substrate, followed by drying at room temperature. UV-Vis spectra were recorded by a JASCO V-670 spectrophotometer at ambient temperature. For recording the spectra of a liquid sample, 500 µl of the sample was added into a silicon cell with light length of 1 cm. For recording the spectra of solid sample, 600 µl of liquid sample was dropped on a silicon slice and followed by drying at ambient temperature. For pure polymers, the concentration of the sample was adjusted to 1 mg ml -1. Fluorescence spectra were measured with a JASCO FP-6500 spectrofluorometer by excitation at 3

4 214 nm with a scan rate of 100 nm s -1. FT-IR spectra were recorded using a Perkin-Elmer Spectrometer, 10 times for each sample, and were Fourier-transformed at a resolution of 4 cm -1. Spectra were corrected with a baseline supported by Perkin-Elmer software. Stock samples were drop-cast onto a gold film substrate, and dried under ambient conditions for measurements. The pristine BNNTs and the polymer powder were used to measure FT-IR spectra for the original BNNTs and pure polymers, respectively. Polymerfunctionalized BNNTs were precipitated from dispersion by using centrifugation at rpm for 25 min, followed by the aforementioned similar redispersion-centrifugation cycles in milli-q to remove free polymers, and were collected as solid products for recording FT-IR spectra. Contact angles were measured by using a Contact Angle Meter Model A-X produced by Kyowa Interface Science Co. Ltd. In each measurement, a water droplet with volume of 3.1 µl was dropped on the surface of the coating. Measurements were carried out after 5 s stabilization. SEM images were recorded using a JEOL model JSM-6390LA SEM operating at 10 kv. 4

5 Figure S1. UV-Vis absorption spectra of BNNTs dispersed in the aqueous solution of (-)PPP (pink), PXT (blue), PSS (green), PVS (red), and PAA (black). 5

6 Figure S2. (a) Aqueous dispersion of PXT-functionalized BNNTs, (b) AFM image of PXTfunctionalized BNNTs, and statistic (c) height and (d) length analyses of PXT-functionalized BNNTs (the total number of BNNTs studied was 96). 6

7 Figure S3. FT-IR spectra of (-)PPP-functionalized BNNTs (red), (-)PPP (blue), and the original BNNTs (black). Importantly, the in-plane stretching mode (longitudinal optical mode: LO) and outof-plane radial bucking mode (transverse optical mode: TO) absorptions of the hexagonal BN network 2 shifted from 1336 cm -1 and 781 cm -1 for the original BNNTs to 1363 cm -1 and 797 cm -1 for the (-)PPP-functionalized BNNTs, respectively. Note that the vibrations at 2945 cm -1 (υ as (CH 2 )) and 2876 cm -1 (υ s (CH 2 )) derived from PPP were found at 2921 cm -1 and 2852 cm -1 for (-)PPPfunctionalized BNNTs, respectively. The vibrations corresponding to benzene (1646 cm -1, 1615 cm -1, 1486 cm -1, 1470 cm -1 ) of (-)PPP disappeared for the (-)PPP-functionalized BNNTs. These results definitively supported that (-)PPP strongly interacted with the BNNT sidewalls via π-π stacking interactions. 7

8 Figure S4. UV-Vis spectra of PPV-functionalized BNNTs (red, after thermal treatment), PXTfunctionalized BNNTs (gray), PPV (blue, after thermal treatment), and PXT (sky blue). Notably, the appearance of the absorption at 410 nm for PPV after thermal treatment in comparison with PXT suggested the successful conversion of PXT into PPV. 3 The broad absorption similarly appeared at around 410 nm for the PPV-functionalized BNNTs, while it was absent for the PXT-functionalized BNNTs, suggesting that the PXT-functionalized BNNTs were successfully converted into PPVfunctionalized BNNTs. 8

9 Figure S5. FT-IR spectra of PPV (green), PPV-functionalized BNNTs (red), PXT-functionalized BNNTs (pink), PXT (blue), and the original BNNTs (black). Importantly, the in-plane stretching mode and out-of-plane radial bucking mode absorptions of the hexagonal BN network shifted from 1336 cm -1 and 781 cm -1 for the original BNNTs to 1345 cm -1 and 795 cm -1 for the PXTfunctionalized BNNTs, respectively. Note that the vibrations at 3021 cm -1 (υ as (CH 2 )) and 2808 cm -1 (υ s (CH 2 )) derived from PXT were found at 2921 cm -1 and 2852 cm -1 for PXT-functionalized BNNTs, respectively. The vibration at 1396 cm -1 (υ(c=c) aromatic in-plane) for the PXT disappeared for the PXT-functionalized BNNTs. These results definitively supported that PXT strongly interacted with the BNNT sidewalls via π-π stacking interactions. After thermal treatment, the LO and TO absorptions shifted from 1345 cm -1 and 795 cm -1 for the PXT-functionalized BNNTs to 1352 cm -1 and 786 cm -1 for the PPV-functionalized BNNTs, respectively. Absorptions at 2921 cm -1 (υ as (CH 2 )), and 2852 cm -1 (υ s (CH 2 )), derived from PXT disappeared for the PPV-functionalized BNNTs, indicating that PXT were factually converted into PPV. 9

10 Figure S6. SEM images of PXT-functionalized BNNTs on silicon wafers (a) before and (b) after thermal treatment. 10

11 REFERENCES 1 Zhi, C.; Bando, Y.; Tang, C. & Golberg, D. Effective precursor for high yield synthesis of pure BN nanotubes, Solid State Commun. 135, (2005). 2 Lee, C. H.; Wang, J. S.; Kayatsha, V. K.; Huang, J. Y. & Yap, Y. K. Effective growth of boron nitride nanotubes by thermal chemical vapor deposition. Nanotechnol. 19, (2008). 3 Shim, H. K. & Jin, J. I. Light-emitting characteristics of conjugated polymers. Adv. Polym. Sci. 158, (2002). 11