J. J. Vilatela, IMDEA Materials Institute, Madrid, Spain 28906 

We report on the synthesis of kilometers of continuous macroscopic fibers made up of carbon nanotubes (CNT) of controlled number of layers, ranging from singlewalled to multiwalled, tailored by the addition of sulfur as a catalyst promoter during chemical vapor deposition in the direct fiber spinning process. The progressive transition from single-walled through collapsed double-walled to multiwalled is clearly seen by an upshift in the 2D (G′) band and by other Raman spectra features. The increase in number of CNT layers and inner diameter results in a higher fiber macroscopic linear density and greater reaction yield (up to 9%). Through a combination of multiscale characterization techniques (X-ray photoelectron spectroscopy, organic elemental analysis, highresolution transmission electron microscopy, thermogravimetric analysis, and synchrotron XRD) we establish the composition of the catalyst particles and position in the isothermal section of the C−Fe−S ternary diagram at 1400 °C. This helps explain the unusually low proportion of active catalyst particles in the direct spinning process (<0.1%) and the role of S in limiting C diffusion and resulting in catalyst particles not being in thermodynamic equilibrium with solid carbon, therefore producing graphitic edge growth instead of encapsulation. The increase in CNT layers is a consequence of particle coarsening and the ability of larger catalyst particles to accommodate more layers for the same composition. 

 
Juan J. Vilatela is a researcher at IMDEA Materials Institute, head of the Multifunctional Nanocomposites group. His research focuses on the development of macroscopic materials made up of nanostructured building blocks that combine traditional properties of high-performance materials (e.g. mechanical) with the ability to take part in energy transfer processes. A key challenges lies in engineering these materials across multiple length scales: tailoring electronic properties on a “molecular” scale to enable charge/energy transfer processes, while also being able to produce bulk quantities that can for example be integrated as reinforcement in polymer composites. He has a BSc in Engineering Physics (Hons) from UIA, Mexico, and a PhD from Cambridge University, obtained in 2009. Before joining IMDEA Materials Institute he worked as a postdoctoral research associate in the Department of Materials Science and Metallurgy at Cambridge University and as a visiting scientist at Prof. M. Terrones’ (IPICYT) and Prof P. Ajayan’s laboratories (RPI). He has around 20 publications (e.g. Science, Adv. Mater.) a book chapter and 4 patents. Currently he coordinates two FP7 projects and 2 industrial projects.