Jeffrey A. Fagan

As project leader for the Nanotube Metrology project at NIST I seek to develop the metrology for, and characterize the fundamental properties of, single-wall carbon nanotubes (SWCNTs).

SWCNTs are an exciting nanomaterial class with many predicted applications. However, the use of these materials has been hindered by uncertainty in fundamental properties and metrics. In general, even defining the purity of a SWCNT sample is a substantial challenge, and one that inserts a large barrier against commerce of the materials.

The class of SWCNT materials is actually comprised of many different species, often called chiralities, of SWCNTs. Each species is defined by how the carbon sheet is rolled up to generate the tube structure, and has its own unique diameter and physical properties. Depending on the species, SWCNTs can be metallic, semi-metallic or semi-conducting in nature, and can have optical band gaps in different parts of the visible and infrared spectrum.

The strategy in my project is to develop the measurement science and fundamental nanotube properties through an iterative process of purification, separation, and measurement. To produce purified fractions we use and develop dispersed phase separation techniques (i.e. on nanotubes individualized in liquids) taken or extrapolated from the biosciences, colloids, and polymers fields. These techniques include the ability to separate SWCNTs by their species, length, and even handedness. By producing better dispersed (i.e. individulized nanotubes in solution), or highly enriched samples with resolved parameters, we enable better (and cleaner) measurements of the fundamental properties of the SWCNTs, which in turn can drive improvement in the purification/separation science. The other outcome of these measurements is that it allows us to develop documentary standards by which these properties should be measured, and to produce reference materials with certified property values.

My personal research efforts revolve around the interogation of the nanotube-solution interface, and in the use of colloid science based techniques for separations. An example of a key technology in use in my lab is ultracentrifugation. Once I have dispersed SWCNTs in a centrifuge, through proper experimental design, I can separate them into fractions with different lengths, diameter distributions, metallics from semiconducting, empty ones from water-filled ones, and even enrich the enantiomeric handedness. This can all be controlled through altering the balance of the forces acting on the nanotubes in the centrifuge, and is effectively accomplished by changing the speed, temperature, amount/kind of surfactant, and-or the liquid density used in the processing. At the right is an example of electronic type sorted nanotubes, and below is a picture of dispersions of long (~ 1 micron) length sorted nanotubes from different synthesis methods.

Highly purified fractions such as these, although these each still contain many species of SWCNTs, are allowing us to develop the metrology and reference materials necessary to enable expanded SWCNT commerce. I also use ultracentrifugation as a powerful characterization tool in my project. Analytical ultracentrifugation, in which we can directly observe the motion of particles during the entrifugation, allows for the characterization of size distributions and interfacial binding characteristics of nanotubes (and other nanoparticles) in their native environments. Most recently I have been characterizing the composition and structure of the water and other materials that can enter into the inside of open-ended nanotubes. This is important, because this material significantly affects the properties of the nanotubes and their behavior during separation processing. From these effects, nanotube species can be misidentified or rendered useless for a particular application. This work builds upon a our separation science basis and is directly made possible by a bulk separation methodology for empty and water-filled nanotubes recently published by my group.

Potential Post Doc Project Areas

1) Protein and Surfactant Corona Measurement on Dispersed Carbon Nanotubes
The shell of protein or surfactant molecules that surround a dispersed nanotube, whether in biological fluids such as serum, or non-biological dispersion dominates many of the interactions of the nanotube with its environment. Measuring the structure and nature of the dispersing molecules will allow for predictions of properties such as the zeta potential, and will provide important information for addressing the effects and potential accumulation sites of dispersed nanotubes in the human body and in the environment. Recent work at NIST and elsewhere are just now beginning to produce nanotube samples with known length, purity and chirality; these purified materials will be the starting point for measuring the structure and nature of the surrounding shell of adsorbed molecules.

2)Purified Nanotubes for Intrinsic Property Measurement
Carbon nanotubes are the subject of intense scientific interest for advanced applications such as biological sensors and flexible conductive coatings because of their remarkable strength and electrical properties. Developing and selecting nanotubes for these advanced applications will require the specific knowledge and demonstration of achievable properties beyond the theoretical predictions. In our recent efforts we and others have made progress towards isolating single length and diameter populations of nanotubes. In this project continued advancement of the separation technology and the optical characterization through multiple metrologies will be pursued.

• 2008-present: Technical Working Area Chair (TWA 34), VAMAS
  
• 2007-present: Chemical Engineer, Polymers Division, NIST
• 2005-2007: NRC Postdoctoral Fellow, Polymers Division, NIST

• Fagan, J.A.*; Sides, P.J.; Prieve, D.C. Langmuir 2006,22, "The Mechanism of Rectified Lateral Motion of Particles near Electrodes in Alternating Electric Fields below One Kilohertz”.
• Fagan, J.A.*; Sides, P.J.; Prieve, D.C. Langmuir 2005,21, 1784-1794. “Evidence of Multiple Electrohydrodynamic Forces Acting on a Colloidal Particle near an Electrode.”
• Fagan, J.A.*; Sides, P.J.; Prieve, D.C. Langmuir 2004,20,4823-4834. "Vertical Motion of a Charged Colloidal Particle near an AC Polarized Electrode with a Nonuniform Potential Distribution: Theory and Experimental Evidence."
• Fagan, J.A.*; Sides, P.J.; Prieve, D.C. Langmuir 2003,19, 6627-6632. "Calculation of AC Electric Field Effects on the Average Height of a Charged Colloid: Effects of Electrophoretic and Brownian Motions".
• Fagan, J.A.*; Sides, P.J.; Prieve, D.C. Langmuir 2002, 18, 7810-7820. "Vertical Oscillatory Motion of a Single Colloidal Particle Adjacent to an Electrode in an AC Electric Field"
• Buckley, P.F.; Fagan, J.A. and Searson, P.C.* J. Electrochemical Society, 2000, 147, 3456-3460. "Analysis of Hydrogen Trapping in Palladium by Modulated Permeation Spectroscopy"