Chirality Affects Aggregation
Kinetics of Single-Walled
Carbon Nanotubes
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Abstract
Aggregation kinetics of chiral-specific semiconducting
single-walled
carbon nanotubes (SWNTs) was systematically studied through time-resolved
dynamic light scattering. Varied monovalent (NaCl) and divalent (CaCl<sub>2</sub>) electrolyte composition was used as background solution
chemistry. Suwannee River humic acid (SRHA) was used to study the
effects of natural organic matter on chirally separated SWNT aggregation.
Increasing salt concentration and introduction of divalent cations
caused aggregation of SWNT clusters by suppressing the electrostatic
repulsive interaction from the oxidized surfaces. The (6,5) SWNTs,
i.e., SG65, with relatively lower diameter tubes compared to (7,6),
i.e., SG76, showed substantially higher stability (7- and 5-fold for
NaCl and CaCl<sub>2</sub>, respectively). The critical coagulation
concentration (CCC) values were 96 and 13 mM NaCl in the case of NaCl
and 2.8 and 0.6 mM CaCl<sub>2</sub> for SG65 and SG76, respectively.
The increased tube diameter for (7,6) armchair SWNTs likely presented
with higher van der Waals interaction and thus increased the aggregation
propensity substantially. The presence of SRHA enhanced SWNT stability
in divalent CaCl<sub>2</sub> environment through steric interaction
from adsorbed humic molecules; however showed little or no effects
for monovalent NaCl. The mechanism of aggregationdescribing
favorable interaction tendencies for (7,6) SWNTsis probed
through ab initio molecular modeling. The results suggest that SWNT
stability can be chirality dependent in typical aquatic environment