Novel Dispersion and Self-Assembly

Transcription

1 Novel Dispersion and Self-Assembly of Carbon Nanotubes Mohammad F. Islam 100g Department of Chemical Engineering and Department of Materials Science & Engineering Funding Agencies Korea-US NanoForum 2010, Seoul, Korea April 5-6, 2010 NSF: CBET , DMR and DMR ACS-PRF Sloan Foundation DARPA

2 Outline Introduction to Soft Materials Single Wall Carbon Nanotubes (SWNTs) Purification, Dispersions and Their Properties Carbon Nanotube Aerogels Conclusions

3 Soft Materials - Introduction

4 Introduction to Single Wall Carbon Nanotubes Diamond C60 Buckminsterfullerene Graphite Single wall Carbon Nanotube (SWNT) Multiwall Carbon Nanotube (MWNT)

5 SWNTs have extraordinary anisotropic properties 100 nm 10,000 nm ~1 nm SWNT Strength (~100x Steel) Tensile strength ~200 GPa Stiffness ~1 TPa Elongation ~30% Salvetat et al., PRL 82, 944 (2000) Electrical Conductivity (~Copper) Dekker et al., Nature 386, 474 (1997) Thermal Conductivity ~3x Diamond Incorporate anisotropic properties of SWNTs into composites

6 Challenges Large scale production of clean nanotubes. Homogeneous dispersion i in solvents and host materials. van der Waals attraction: 40 KBT/nm Control of diameter, chirality and length. Determination of bulk properties and structural behavior. Effective integration into composites. Controlled integration into electronic circuits.

7 Synthesis of SWNTs Research Experience for Undergraduates 2007 Hata et. al., Science 306, 1362 (2005)

8 Purification of SWNTs Standard wet air burn with H 2 O 2 Mild acid reflux Magnetic gradient fractionation Vacuum anneal Flow in nanotube Collect 20 nm suspension magnet magnetically fractionated nanotubes 20 nm -3 M (emu u/mg) x Purification only LMNT Purified LMNT puried and Fractionated HiPCO Purified HiPCO Purified and Fractionated Fractionated H (Tesla) Inten nsity x Nature Materials 4, 589 (2005) wavenumber (cm -1 )

9 Surfactants Surfactant + micelle Hydrophobic tail Hydrophilic headgroup water oil Shake water water Oil droplets +

10 Dispersing SWNTs: Our Work Sodium Dodecyl Benzene Sulfonates (NaDDBS) C 12 H 25 SO 3- Na + Surfactant: SDS TX-100 NaDDBS SWNTs: 3x10-4 6x10-4 2x10-2 Time: 5 days 5 days 2 months m Nano Letters 3, 269 (2003)

11 Purified and Suspended SWNTs Are Undamaged 0.5 Optical Properties 50 Absorb bance Emiss sion Electrical Properties Wavelength (nm) 6 5 Metallic (x5) t (na) Curren Semiconducting (x10) Nature Materials 4, 589 (2005) Gate Voltage (V)

12 Aerogels: Ultra-light light Mesoporous Materials Ultra-light Highly porous materials Very high strength-to-weight to Very high surface-area-to-volume ratio Ultra-light structural media Radiation detector Thermal insulator Battery electrode Supercapacitor Aerogel type Electrical Thermal Conductivity Density (g/cm 3 ) Conductivity (S/cm) (W/m-K) Silica N/A ~ ~ 0.1

13 Rigidity Percolation Network formation 10 5 at low Strong network Pl ateau Modulus s, G' (Pa a) Phys. Rev. Lett. 93, (2004)

14 CNT Aerogels Increasing CNT concentration Phys. Rev. Lett. 93, (2004) NanoLetters 6, 313 (2006) CNT gels do not break apart

15 CNT Aerogels Density: 0.02 g/cm 3 1 µm Advanced Materials 19, 661 (2007)

16 SWNT Aerogels 100g weight on 3 aerogel posts Total aerogel mass: 12.8 mg Density 0.02 g/cm 3 Supports at least ~8,000x own weight 100g 10 µm SWNT Aerogel posts 20 nm Electrical Conductivity up to ~10 S/cm Surface area 1860 m 2 /g Thermal Conductivity ~0.3 W/m-K Advanced Materials 19, 661 (2007) 3 µm

17 CNT Aerogels Current (ma) Voltage (V) -1500

18 Backfilling with epoxy Epon 828 Resin +EpiKure 3234 Crosslinker Vacuum Aerogel Epoxy + cross linker Resin wicks into sample Vacuum removed Conductivity i largely l unaffected by backfilling Improved composite conductivity Adv. Mater. 17, 1186, 2005 Fracture - Complete fill Can be backfilled with various substances

19 Fusing CNT Aerogel PRL 89, (2002)

20 Fusing CNT Aerogel Nature Nanotech. 3, 17 (2008)

21 Fusing CNT Aerogel Irradiation gives rise to covalent bonds between the tubes. The overall strength th of the nanotube materials may increase. Increase the tensile strength of macroscopic nanotube products. A beneficial effect on the electronic properties Irradiation with moderate doses may increase the conductivity of nanotube networks. Spatially localized irradiation can be used for creating functional electronic nanotube-based devices. Is it possible to fuse CNTs in 3D structure?

22 Fused CNT Aerogel

23 Fused CNT Aerogel

24 Fused CNT Aerogel Defects on CNTs A fused CNT junction

25 Fused CNT Aerogel J (A/cm 2 ) HP Outside_hole holder_400v_annealing Outside_carbontape_200V_annealing Voltage (V)

26 Conclusions We fabricated self-assembled carbon nanotube based ultra-light, li large surface area-to-volume ratio electrically conducting porous structure CNT aerogel. CNTs can be fused at junction points to increase mechanical strength and thermal properties. 100g