|M.Sc Student||Granite Meirav|
|Subject||Interaction of Single-Wall Carbon Nanotubes with Polymers|
and Synthetic Polypeptides
|Department||Department of Chemical Engineering||Supervisor||Professor Yachin Cohen|
|Full Thesis text|
Single-wall carbon nanotubes (SWCNT) are exciting new materials. In production they tend to form bundles with different diameters and chirality, which hinder their applicability and realization of their unique properties. This research is aimed to understand the interactions between SWCNT and specific block copolymers and polypeptides, in order to functionalize them for practical further use. In this research Pluronic F108 - (Ethylene oxide)132(Propylene oxide)50(Ethylene oxide)132 - an amphiphilic block copolymer was investigated alongside with PFFDD - a synthesized short polypeptide of about 6 units, containing alternating hydrophobic block of two phenylalanine (FF) and hydrophilic block of two aspartic acid (DD).
Aqueous SWCNT/F108 dispersions were prepared by sonication and light centrifugation to remove catalyst particles and amorphous carbon. These exhibited homogenous stable ink-like dispersions. Cryo-TEM images of both systems revealed isolated, very small bundles of carbon nanotubes, with diameters range from 1 to 5 nm and approximately 500 nm length. SANS experiments were conducted at six different contrasts (different D2O/H2O content of the dispersing solvent). The observed scattering patterns suggested a complex entity with a heterogeneous structure. A near-matching contrast was found at 70% D2O, at which the low scattered intensity exhibited almost a q-1 power-law for the entire range of scattering vector q, an indication of rod-like entities. Modeling of the scattering patterns indicated a complex entity consisting of three layers. First is a thin core rod-like bundle, containing four nanotubes with a total averaged radius of 20 Å. Second is a PPO shell, about 18 Å thick, adsorbed compactly onto the nanotube core. Third are the PEO chains, which loosely emanate from the core-shell rod structure, with a rather large gyration radius of about 120 Å. An area of 170 Å2 is estimated for each PEO chain at the PPO-water interface. The model fit required special considerations of tight association of water molecules around PEO and slight isotopic selectivity. Cryo-TEM images of the PFFDD solution, as well as SANS measurements which revealed a q-3 power law, indicated large aggregates with ill-defined surfaces. Images of SWCNT/PFFDD dispersions revealed isolated bundles of carbon nanotubes with small diameter and high length.