Consistent with earlier investigations of both SWCNT-polymer composites, AFM imaging showed no difference in the height of PEI 30 -SWCNTs and chitosan-SWCNTs (AFM height h = 5 nm). The identical AFM height values are in contrast to the different hydrodynamic diameter values of 15 nm and 150 nm of PEI-SWCNT and chitosan-SWCNT, respectively. This indicates a different thickness of the ion layers surrounding the polymer-coated SWCNT (Supporting Text 4). While both PEI 30 -SWCNTs and chitosan-SWCNTs showed a high positive zeta potential, the AFM images revealed that only PEI 30 -SWCNTs exhibited aggregations along their sidewalls (C.F. carboxylated SWCNT (ζ = -70 mV), Fig. ). We found that PEI-SWCNT preparations with inefficient sonication and with a hydrodynamic diameter greater than ~15 nm (i.e., contains aggregates. Fig. , panels 2 and 4, Fig. ) precipitated over time. We also found that an efficient probe-tip sonication rather than bath sonication is essential to generate a colloidal dispersion of PEI-SWCNT.