Instructor: Jeffrey Fagan, National Institute of Standards and Technology

Single-wall carbon nanotubes (SWCNTs) are underpinning emerging technologies and applications in bio-sensing, single photon sources, and semiconductor chip applications.  However, these application areas are enhanced or best enabled through the use of single nanotube structure (species) populations not directly available from commercial synthesis methods. Isolating specific species, denoted by a chiral index (n,m) and often termed "chiralities," can be accomplished through liquid-phase processing methods, as can refinement in length distribution and general purity in several senses.

In this tutorial the instructors will present an overview of the many SWCNT separation methods developed for isolating particular sub-populations of nanotubes through liquid-phase processing of SWCNT dispersions.  These will include separation by species (chirality), length, general purity, and even enantiomeric handedness of a single (n,m) structure.  Methods for optical characterization of achieved separations will also be presented in detail.

Learning objectives of this tutorial include: 

• An overview of SWCNT structure diversity and its control of nanotube material properties. Different nanotube synthesis methods generate populations of (n,m) species of distinct average diameter; the diameter strongly affects material properties such as the electronic band gap and mechanical stiffness.  Selection of an optimal source material for different applications will be presented.
• Presentation of the diverse set of methods developed to sort nanotubes by: length, species, and enantiomeric handedness.

• Many separation methods have been developed for isolating various sub-populations of nanotubes using liquid-phase processing.  A survey of the different methods that have been developed, their equipment requirements, and general evolution towards more resolving techniques will be presented.
• Methods for characterization of achieved separations and the limits and advantages of each technique.
• To measure the success of separations, it is necessary to have methods that can measure changes in the distribution of the SWCNT population.  Different manners of separation, such as length or species separation, require different measurement methods, and their effectiveness can vary depending on the specific equipment and type of SWCNT being measured.  We will present an overview of several methods useful for characterizing nanotube populations and discuss the advantages and disadvantages of commonly used techniques.
• Specific and detailed discussion of the use of aqueous two-polymer phase extraction (ATPE) methods for (n,m) species selection.
• ATPE is a widely utilized technique for isolating specific (n,m) SWCNT species through an extraction process controlled by either a DNA-dispersant sequence, or the competition between two different surfactants.  This section will highlight the underlying basis of ATPE, the process for deciding on an ATPE separation strategy, and description of extraction experiments resulting in separated single (n,m)s (and/or enantiomers thereof) for different diameter ranges of starting populations.  Discussion of the practical implementation of ATPE in an academic lab setting will be described with guidelines for performing successful separations.