|M.Sc Student||Karawany Tamer|
|Subject||Investigation the Mechanism by which Single Stranded ssDNA|
Adsorbs onto Single-Walled Carbon Nanotubes
|Department||Department of Chemical Engineering||Supervisors||Professor Simcha Srebnik|
|Professor Yachin Cohen|
|Full Thesis text|
Single-walled carbon nanotubes (SWCNTs) have unique properties due to their chirality and high symmetry. Current techniques of sorting SWCNTs into semiconducting and metallic species are only partially successful due to their poor solubility and hence difficulty in forming a dispersion. Recently, it has been found that ssDNA sequences interact strongly with SWCNTs to form stable dispersions, and allows for their separation into different chiral fractions. This research is aimed at understanding the nanostructure of ssDNA-SWCNTs aqueous dispersions and the difference of interaction between specific ssDNA sequences. Polythymine (T)12 and polyguanine-thymine (GT)6, as well as poly (styrene-alt-maleic acid) were investigated using AP-grade SWCNTs with two different diameter ranges.
Aqueous dispersions of SWCNTs and ssDNA oligomers were prepared by sonication and slight centrifugation, resulting in homogenous black dispersions. SWCNTs with larger diameters were somewhat easier to disperse, most likely due to the larger contact area. Cryo-TEM images obtained from these dispersions revealed well-dispersed individual nanotubes of 2-5 nm diameter, as well as large bundles with diameters ranging from 15 to 25 nm. Small Angle Neutron Scattering (SANS) experiments of these dispersions were conducted at 100% D2O, the intensity profiles for both dispersions showed q-1 and q-3 power laws for the small and large q range respectively, which indicate heterogeneous large cylindrical aggregates. A cylinder model with an average radius of 18 nm resulted in a good fit to the data. Absorbance spectra of SWCNT-T12 and SWCNT-(GT)6 dispersions revealed higher SWCNT concentration in the T12 dispersion which indicate that T12 is a better disperser than (GT)6.
SANS experiments of these dispersions were also conducted at different D2O/H2O contrasts, as well as for the bare ssDNA oligomers. Minimal scattering was obtained at 70% and 75% D2O, respectively, indicating the matching points of the solutions. Therefore, the difference between the SLD of the DNA and that of the SWCNT is very small, and makes it hard to distinguish them from one another using SANS. Scattering data from this hybrid at 75% D2O, after background subtraction, showed q-3 behavior, which indicates large aggregates with a rough surface, suggesting ssDNA oligomers collapsed on the nanotubes.