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NOV 12, 2014 8:00 AM PST

Analytical Ultracentrifugation of Carbon Nanotubes

Speaker
  • Chemical Engineer, Lead Scientist, National Institute of Standards and Technology
    Biography
        Dr. Jeffrey Fagan is a staff scientist in the Materials Science and Engineering Division at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland. Part of the Complex Fluids group, he currently leads the Particles, Tubes, and Colloids Project, which is addressing metrological and processing barriers for single-wall carbon nanotubes (SWCNTs) and other nanomaterials in the service of NIST's role in promoting US commerce.
        From his activities at NIST, Dr. Fagan is an author on 50+ peer-reviewed publications in the areas of colloidal and nanoparticle science. Prominent publications including multiple methodologies for the fractionation and characterization of dispersed carbon nanotube materials for specific properties, and the characterization of dispersed particle properties via analytical ultracentrifugation. Current activities include a continued focus on separating SWCNTs by their physical properties, and characterizing nanoparticle populations via analytical ultracentrifugation. 
        Dr. Fagan additionally serves as the lead scientist for the production of SWCNT reference materials (RMs) and standard reference materials (SRMs) at NIST, and is the chair of technical working area 34 under the Versailles Project on Advanced Materials (VAMAS, an international pre-standardization organization), focused on fostering development of metrology standards for nanoparticle populations.
        Dr. Fagan has won multiple awards for his work at NIST, including a 2010 Presidential Early Career Award for Scientists and Engineers (PECASE), a NIST Bronze Medal in 2009, a Department of Commerce Silver Medal in 2013, the NIST Sigma Xi chapter's Young Investigator Award in 2013, and a National Research Council post-doctoral fellowship in 2005. Dr. Fagan had earned his BS degree in chemical engineering from Johns Hopkins University in Baltimore, Maryland, and his Ph.D. in chemical engineering from Carnegie Mellon University in Pittsburgh, Pennsylvania.

    Abstract

     

      Sedimentation velocity (SV) experiments on dispersed nanoparticles are a powerful method for determining otherwise hard to evaluate properties of the nanoparticle such as the density and size of the adsorbed interfacial layer, or for a direct evaluation of the entire distribution of a property such as particle size. The ability to measure these properties in situ in either aqueous or non-aqueous media, and via multiple detection techniques, provides information not readily available through other methods such as electron microscopy. My research has focused in particular on utilizing the capabilities of sedimentation velocity methods for the characterization of single-wall carbon nanotubes (SWCNTs).

      Single-wall carbon nanotubes are a family of chemical species comprised entirely of a “rolled up” single layer hexagonal lattice of carbon. Depending on the diameter of the formed cylinder, and the vector of the hexagonal lattice relative to the tube axis, these nanoparticles can be metallic, semi-metallic or semi-conducting, each having unique optical, mechanical, thermal, and electrical properties. Many of the applications for this set of materials however depend on the properties of the material when dispersed in the liquid phase, or contain liquid phase processing steps. The key aspects of liquid phase dispersion and processing though hinge on controlling the properties of the interfacial layer between the nanotube and the solution to enable dispersion, selective fractionation and/or biocompatibility. Density contrast variation methods combined with sedimentation velocity experiments provide a high resolution methodology for evaluating this interface. I will present results detailing the use of such density contrast techniques on the characterization of the interfacial layer on specific SWCNT species that demonstrate the power of analytical ultracentrifugation to resolve this interfacial layer.

      Separately, a second critical factor for SWCNT use in dispersion form is the size distribution of the dispersed population; this distribution strongly affects the transport of the nanotubes in many environments as well as the achievable properties in end applications, and is thus a necessary parameter for quality control. Measuring the whole size distribution of a nanoparticle is however typically very challenging for non-monodisperse particles. In a second set of results, I will show that the distribution of sedimentation coefficients for SWCNTs can be used to calculate through hydrodynamic theory the size distribution of the population in the dispersion in quantitative agreement with other techniques such as atomic force microscopy (AFM).
    What you will learn:

      Methodology for the characterization of an important class of nanomaterials via SV, particularly involving variations of density contrast experiments to elucidate different interfacial parameters.
    Discussion of concerns, details, assumptions, and problems in utilizing SV for nanoparticles, including some considerations for overcoming these issues through experimental methodology.

    Learning Objectives:

    • Understand how sedimentation velocity (SV) experiments on dispersed nanoparticles are a powerful method for determining otherwise hard to evaluate properties of the nanoparticle such as the density and size of the adsorbed interfacial layer
    • Understand how to utilize the capabilities of sedimentation velocity methods for the characterization of single-wall carbon nanotubes (SWCNTs)

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