  Aqueous dispersions of exfoliated, bile-salt stabilized single-wall carbon
nanotubes exhibit a first order transition to a nematic liquid-crystalline
phase. The nematic phase presents itself in the form of micron-sized nematic
droplets also known as tactoids, freely floating in the isotropic host
dispersion. The nematic droplets are spindle shaped and have an aspect ratio of
about four, irrespective of their size. We attribute this to a director field
that is uniform rather than bipolar, which is confirmed by polarization
microscopy. It follows that the ratio of the anchoring strength and the surface
tension must be about four, which is quite larger than predicted theoretically
but in line with earlier observations of bipolar tactoids. From the scatter in
the data we deduce that the surface tension of the coexisting isotropic and
nematic phases must be extremely low, that is, of the order of nN/m.
