Structure of semidilute single-wall carbon nanotube suspensions and gels.

The microscopic network structure of surfactant-stabilized single-wall carbon nanotubes (SWNTs) in water was investigated as a function of SWNT concentration in the semidilute (overlapping) regime using small-angle neutron scattering (SANS). Most of the samples exhibit rigid rod behavior (i.e., Q(-1) intensity variation) at large scattering wavevector, Q, and a crossover to network behavior (i.e., approximately Q(-2) intensity variation) at low Q. The mesh size, xi, of the network was determined from the crossover of rigid rod to network behavior in the SANS intensity profile and was found to decrease with increasing SWNT concentration. When the dispersion quality of these associating rigid rods was degraded, only approximately Q(-2) intensity variation was observed at both high and low Q. Small-angle X-ray scattering measurements of the same stable dispersions were relatively insensitive to network structure because of poor contrast between SWNTs and surfactant.