Dispersion
of Carbon Nanotubes Using Mixed Surfactants:
Experimental and Molecular Dynamics Simulation Studies
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Abstract
The
ability of cationic-rich and anionic-rich mixtures of CTAB
(cetyltrimethylammonium bromide) and SDS (sodium dodecyl sulfate)
for dispersing of carbon nanotubes (CNTs) in aqueous media has been
studied through both the experimental and molecular dynamics simulation
methods. Compared to the pure CTAB and SDS, these mixtures are more
effective with the lower concentrations and more individual CNTs,
reflecting a synergistic effect in these mixtures. The synergistic
effects observed in mixed surfactant systems are mainly due to the
electrostatic attractions between surfactant heads. In addition, the
surface charge related to the colloidal stability of mixed surfactant-covered
nanotubes has been characterized by means of ζ-potential measurements.
The results indicate that the hydrophobic interactions between surfactant
tails also give rise to the higher adsorption of surfactant molecules.
Furthermore, molecular dynamics (MD) simulations have been performed
to provide insight about the structure of surfactant aggregates onto
nanotubes and to attempt an explanation of the experimental results.
The MD simulation results indicate that the random and disordered
adsorption of mixed surfactants onto carbon nanotubes may be preferred
for a low surfactant concentration. Our research may provide experimental
and theoretical bases for using mixed surfactants to disperse CNTs,
which can open an avenue for new applications of mixed surfactants