NSF NIRT Grant Hierarchical Nanomanufacturing of Carbon Nanotube Sheets and Yarns and their Applications for Active Nano-Materials Systems PIs: Ray H. Baughman, 1 Karen Lozano, 2 Anvar Zakhidov, 1 and Mei Zhang 1, 3 1. University of Texas at Dallas, 2. University of Texas - Pan American, and 3. Florida State University I. Obtain and Deploy Deep Understanding of Sheet and Yarn Fabrication processes Fig. 1 (A) SEM image from movie showing the transformation of 300  m high nanotube forest (left) to nanotube sheet (right). B: Picture of the continuous draw of a nanotube sheet and the wrapping of this sheet on a rotating mandrel. Problem: Very few types of nanotube forests are drawable to make yarns and sheets, and minor changes in reaction conditions causes a transition from drawable forests to undrawable forests. Results:  The number of nanotubes per forest area must be in a narrow range in order to obtain the degree of intermittent bundling needed for sheet or yarn draw.  Using movies of the drawing process taken in a SEM (Fig. 1A), a model explaining the transition from vertically aligned nanotubes in forests to horizontally aligned nanotubes in nanotube yarns and sheets was derived.  Increased nanotube length in spinable forests nearly ten fold, from 0.3 mm to 2.7 mm.  Synthesized nanotube forests having improved topology that enabled sheet draw at 30 m/minute.  False twist and liquid-based densification provide comparable yarn strengths as those we obtain using twist-based spinning. II. Determine and Understand Sheet and Yarn Properties Fig. 2 (Left) Thermal conductivity measurements on individual nanotube bundles show that bundling dramatically decreases thermal conductivity. (Right) Unlike for graphite yarns, thermal conductivity is unaffected by the small radius bend shown for a nanotube sheet. Results:  The measured thermal conductivity (3  method) of yarns (26 W/mK) and yarns (50 W/mK) is not high.  The strong observed dependence (Fig. 2) of thermal conductivity on nanotube bundling provides the explanation.  Inter-tube connections are relatively unimportant for limiting both phonon and electronic transport, since individual bundle and bulk measurements (normalized to density) differ little.  Network models indicate thermal and electrical transport on all walls of 8 wall, hundred  m long nanotubes.  Experiment and theory show mechanical stress transfer is low between outer and inner MWNT walls for above long nanotubes.  Individual MWNTs break, rather than slide out, when pulled from a twisted 10  m diameter yarn made of 8 wall, hundred  m long nanotubes.  Thermal expansion is negative at RT for twisted yarns (about -3.4X10 -6 /ºC).  Filtration-produced nanotube sheet shows abrupt switch in the sign of Poisson’s ratio vs MWNT weight percent. Fig. 3 (A) Measured in-plane Poisson’s ratio (black) and density-normalized Young’s modulus (blue) vs. MWNT content in SWNT/MWNT sheets. The insert illustrates the effect of Poisson’s ratio sign on transverse curvature for a bent sheet strip. (B) Measured density-normalized tensile strength (black) and density (blue) vs. MWNT content in sheets. (C) Model for nanotube sheets, where meandering nanotubes are represented by zigzag chains. (D) The relationships between in-plane and thickness-direction Poisson’s ratios for SWNT (black) and MWNT (red) sheets having the force constant ratios R that yield the measured Poisson’s ratios (closed circles). The Poisson’s ratio changes results from varying the indicated average angle between the nanotubes and the sheet plane. Poisson’s ratios to the right of the blue line provide negative linear compressibilities. III. Demonstrate Sheet and Yarn Applications for Active Nano-Materials Systems Fig. 4 (Left) MRI imaging of a 3 mm mouse brain and 250  m blood vessel using carbon nanotube antenna, in collaborative work with Tursiop International (UTD licensee). (Right) Self- supporting 50 nm thick, transparent nanotube sheets mounted in metal frames for electron stripping in an ion beam accelerator. Results:  Demonstrated two new applications for MWNT sheets (Fig. 4), MRI antennas and transparent grids for electron stripping.  Demonstrated that twist-spun MWNT yarns provide high actuator strokes (up to 0.5%) at high loads (30 MPa, versus the 0.3 MPa stress generation capability of natural muscles) and low creep even at these high loads. IV. Demonstrate First Synthesis Route to Carbon Nanotubes of One Predetermined Type Fig. 5. A proposed synthesis route to carbon nanotubes of one type. Solid-state 1,4-addition polymerization reaction (A) converts linear stacks of cyclic tetradiyne molecules [-(CH 2 ) 4 C  C-C  C-] 4 (B) into a hydrocarbon nanotube (C), which is the proposed precursor to the (4,4) nanotube (D). Results  Synthesized and purified dimer through hexamer.  Crystal structure determined (Joe Reibenspies, Texas A&M) for trimer phases and two tetramer phases - reactivity is consistent with theory.  Two polymerizable tetramer phases were found, one with the tetramer rings skewered on an array of chloroforms.  When polymerized, both provide the expected Raman spectra for the hydrocarbon nanotube. AB Motor Nanotube Forest