DOW Graduate Seminars: Single Walled Carbon Nanotubes in Liquids
|Event Date:||April 22, 2008|
|Speaker:||Dr. Matteo Pasquali|
|Speaker Affiliation:||Department of Chemical and Biological Engineering, Rice University|
|Time:||3:30 - 4:30 pm
Single Walled Nanotubes (SWNTs) have remarkable electrical, thermal, and mechanical properties. SWNT fibers, sheets, and coatings could be the ultimate building blocks of strong, ultra-light multifunctional materials, electromechanical actuators, sensors, fuel cell membranes, displays, printable electronics, and many other devices where mechanical integrity, electronic properties, thermal transport, ilight weight, and high surface area are important. After the achievement of scalable production of SWNTs, the difficulty of processing pristine SWNTs by liquid-phase methods has been the single most important roadblock to manufacturing macroscopic materials and devices composed principally of SWNTs.
This talk shows that SWNTs dissolve at high concentration in acids; the SWNTs are stabilized because acids protonate their sidewalls, balancing wall-wall van der Waals forces. Acid strength controls the phase behaviour. At low concentration, SWNTs in acids dissolve as individual tubes which behave as Brownian rods. At higher concentration, SWNTs form a highly unusual nematic liquid crystalline phase consisting of entangled domains; these domains are self assembled supermolecular strands of mobile, solvated tubes in equilibrium with a dilute isotropic phase. Under anhydrous condition, the liquid crystal can be processed into continuous highly aligned fibers of pure SWNTs.
By using a new fluorescent staining technique, we measure the rotational diffusivity and persistence length of SWNTs suspended in water with the aid of surfactants, and show that SWNTs behave as Brownian rods. We combine this understanding of stabilized SWNTs in water with principles of rheology and free surface fluid mechanics to design processes for making thin sheets for fuel cell electrodes and electrically conductive, transparent coatings.