Abstract:
Single walled carbon nanotubes (SWNTs) have potential application in fabrication of
nanodevices and sensors. SWNTs are mostly studied as dispersed colloidal solution
in non-aqueous solvents like DMF, due to ease in chemical modification and
transferability required in the fabrication of such devices. These kinetically stable
dispersions help us to understand intermolecular interactions, their solubility and rate
of aggregation. These rates depend upon electrical double layer and surface
charges of SWNTs. The present work is to determine the stability of SWNTs
dispersions in the presence of various coagulants. The stability is discussed keeping
in mind the Schulze-Hardy rule and DLVO theory, which has been traditionally used
to understand colloidal solutions. While stability of SWNT dispersion is typically
desired, aggregation of SWNTs with coagulants and interaction of SWNTs among
themselves are affected by size, shape and ionic strength of coagulants; which leads
to changes in electrodynamic repulsive and van der Walls attractive forces acting
between SWNTs. The study ascertains the relation between Critical Coagulation
Concentration (CCC) of SWNT solutions with various inorganic coagulants (like
NaBr, CuCl2, FeCl3) and that of traditionally considered spherical ions in colloidal
solutions. CCC is the concentration above which onset of rapid aggregation occurs.
Along with experimental results of Schulze-Hardy law for nanotubes, novel photon
enhanced aggregation in these solutions is also observed. We observed
dependence of aggregation rate on optical excitation and band gap energy of
individual nanotubes. Photon enhanced aggregation of SWNTs is observed and
characterized using spectroscopic techniques. This, dependence of stability of
dispersion [CCC] on optical excitation and dielectric property of SWNTs (metallic and
semiconducting) is experimentally demonstrated.
