Carbon Nanotubes

Since the official discovery of carbon nanotubes in 1991, a wide range of investigations have been targeting a large number of potential applications in different areas of engineering. The NanoMaterials Research group at Drexel University works on Carbon Nanotubes and their Applications. It is headed by Professor Yury Gogotsi, and currently includes Dr. Sayan Bhattacharyya (group leader), Dr. Jun Jie Niu, Dr. Isabel Knocke, Mr. Riju Singhal, Ms. Patricia Valenzuela, Ms. Valarie Pelletier, Ms. Elina A. Vitol, and Ms. Prineha Narang.

Carbon Nanopipes for Nanofluidic Devices and In-situ Fluid Studies

The processes that govern fluid processes in pipes are well understood for diameters in the range of micrometers and above. As the diameters diminish (e.g. in the range of a few nanometers), the role of surface tension and capillarity is seen to change, as well as their dependence on material properties. Thus, the expected promise of carbon nanotubes in technological applications is in urgent need of a well-documented basic understanding of such forces, especially since no consistent experimental data have been collected so far. We have determined the liquid/vapor distribution in nanotubes, interaction of the fluids with the nanotube walls as well as the effect of the hydrothermal treatment on the carbon nanotubes. On that basis, an experimental program has been developed that thoroughly explores the various aspects of phase interfacing in a number of nanotube situations, specially closed nanotubes. Fluid behavior, chemical modification, metallization, and opening of the nanopipes have also been investigated using bipolar electrochemistry. The experimental work is supplemented by modeling based on parallel molecular dynamics simulations, which offers a precious set of data for the elaboration of a model based on precise experimental observations.

TEM image of water inclusion inside carbon nanotube and HyperChem simulation of water in a (30, 30) nanotube of 4.07 nm diameter [Nano Lett. 4, 2237 (2004)]

Keck Institute for Attofluidic Nanotube-based Probes

The group is also involved in developing multifunctional nanoscale probes based on engineered carbon nanotubes [Appl. Phys. Lett. 90, 103108 (2007)] and carbon nanopipettes, for controlled transfer of attoliter (10-18 liter) fluid volumes into specific cell organelles. The project funded by W. M. Keck Foundation has made significant strides in achieving the goal with strong collaborations from Department of Electrical and Computer Engineering, Department of Biochemistry and Molecular Biology, School of Biomedical Engineering, Science & Health Systems, and Department of Mechanical Engineering and Mechanics of Drexel University. Details about the project can be found at: www.nano.drexel.edu/KeckInstitute

Multifunctional Carbon Nanotubes Loaded with Nanoparticles

Carbon nanotubes can be loaded with a variety of metal/alloy/metal oxide or carbon nanoparticles and drugs to functionalize them as nanoscale maneuvers during magnetic assembly, nanoscale thermosensors, drug delivery vessels and for supercapacitor applications. The nanotubes are prepared in our laboratory by chemical vapor deposition (CVD) inside porous alumina membranes and the pores are invaded with only few drops of the laboratory synthesized colloidal nanoparticle solution. The alumina membrane is dissolved in an alkaline solution to produce individual filled carbon nanotubes. The nanoparticles can also be embedded in the inner wall of the carbon nanotubes and the loading of the nanoparticles can be quantitatively controlled.

Optical image of ferrofluid filled carbon nanotubes [Nano Lett. 5, 879 (2005)]

Nanoscale Corona Discharge in Liquids

The group has recently demonstrated non-thermal corona discharge in liquid solutions [Angew. Chem. Int. Ed. 47, 8020 (2008)] at tips of conducting electrodes having a nanoscale radius of curvature (carbon nanotube ends and tip of carbon nanopipettes). This method is applied for localized synthesis and deposition of various metal/alloy nanoparticles at specific locations of the carbon nanostructures with a single nanosecond pulse generating cold plasma discharge in liquids. The gold nanoparticle coated carbon nanotubes and nanopipettes have shown significant applications as surface enhanced Raman spectroscopy (SERS) probes and optical sensors in cellular studies. This plasma enables optical emission spectroscopy and multi-elemental analysis at the part per million (ppm) level. The research is in progress in collaboration with Drexel Plasma Institute and Department of Electrical and Computer Engineering, Drexel University.

Optical micrographs of typical coronas around (a) electrode tip, (b) bundle of multiwalled carbon nanotubes, and (c) gold nanoparticle coated carbon nanopipette [Adv. Mater. (2009)]

Conducting Carbon Nanotube Films and Coatings

It is a high time to replace Indium tin oxide (ITO) coatings on transparent and electrically conductive materials, since ITO cannot be used where a combination of conductivity and flexibility is required and is also expensive. We replaced ITO with multi-walled carbon nanotube (MWNT) coatings [Adv. Funct. Mater. 18, 2322 (2008)] that would be a viable candidate for providing sufficient conductivity for most applications, but without the price tag and physical limitations of the current ITO or SWNT coatings. Flexible mats of electrospun PA11 nanofibers (synthesized in our nanofiber electrospinning unit) coated with MWNTs enables the manufacturing of thin (0.1–1 mm) conducting 2-D networks. The advantage of the developed technique is that MWNTs do not form a uniform coating but a percolated network of MWNTs, guided by polymer nanofibers, thus improving the transparency of the film. When annealed in air at 450oC, the transmittance increases to 96% with little effect on the resistance. As the number of MWNT depositions increases, the resistance drops to 150 kΩsq-1 maintaining a constant transmittance of ~85%. The thinnest films, having the highest MWNT coverage, lead to the best combination of electrical and optical properties.

SEM images of MWNT deposited PA11 fiber mats.