Jeffrey A. Fagan

Understanding the structure and properties of dispersed colloidal and nanoparticle fluids is a key technological challenge for initiatives as wide ranging as stabilizing drug suspensions, to fabricating electronic devices, and understanding the fate of nanoparticles in the body/environment.

My interests are in developing the measurement science necessary to monitor critical measurands for dispersed nano and colloidal particles such as size and charge distributions, the structure of surface adsorbed coronas on dispersed particles, and dispersion quality.

In the area of single-wall carbon nanotubes (SWCNTs) research, I have been working on developing the measurement science of these properties, and the intrinsic optical and electronic properties of the nanotubes, through a cyclical strategy of purification, separation, and measurement. Producing better dispersed and highly resolved fractions by variables such as the nanotube length, electronic type, or diameter, allows for better measurements, which allow for the production of better materials.

A key technology that I use is ultracentrifugation. For carbon nanotubes, separation is possible by length, diameter, electronic property, and enantiomeric handedness, with the type of separation that occurs dependent on the speed, temperature, surfactant type(s), and the liquid density used in the processing. At the right is an example of electronic type sorted nanotubes.

Interestingly, not many people realize that single-wall carbon nanotubes are not black. Each individual chirality, the way in which the nanotube is rolled up, has its own distinct optical transition and thus color. These colors also become apparent when the nanotubes are purified through length separation. Matt Becker and I invented the process for length separation of the nanotubes in the centrifuge. The different colors in the liquid below are due to the different distributions of tube chiralities within the samples; each liquid contains ~ 15 – 25 different kinds of SWCNTs.

These highly purified fractions are allowing us to develop the metrology and reference materials necessary to enable expanded SWCNT commerce.

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.

3) Surfactant Structures at High Pressure
Recent work in separating carbon nanotubes via centrifugation has highlighted the lack of measurements and metrology for aqueous surfactant solutions under high hydrostatic pressure. Development of this metrolgy, particularly through neutron scattering, is of interest.

• 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"