|Ph.D Student||Gazit Oz|
|Subject||Self-Assembly of Metal Nanoclusters in Block Copolymer as a|
Template for Photonic Bandgap Materials
|Department||Department of Chemical Engineering||Supervisors||Ms. Rina Tannenbaum|
|Professor Yachin Cohen|
|Full Thesis text|
This thesis deals with the preferential self-assembly of metallic nanoparticles (NPs) in an ordered block copolymer (BCP) matrix with the objective to form a self-assembled photonic bandgap material (PBG). The novel path we chose to sequester the metallic NPs in a specific domain of the BCP, follows a "one-pot" process consisting of the in-situ thermolysis of metal carbonyl precursors (MCPs), with the polymer acting both as the matrix and as the capping agent for the NPs. Previous studies on this type of reactions, when performed in a polymer melt above the glass transition temperature (Tg), have shown the formation of NPs that retain the characteristic monodisperse. Therefore, we first investigated the possibility of synthesizing the NPs in a pre-ordered BCP film, inherently below its Tg. We found that the morphology of the NPs formed below Tg is highly sensitive to the system temperature, and differs significantly from their morphology above Tg. The glassy state was found to have dramatic effect on PMMA kinetics while no effect on PS. Since this path has produced broad polydispersity (PD) and polymorphism of the NPs, it does not suite optical applications. Therefore, synthesis was conducted in a BCP solution. The rates of reactions performed in a BCP solution were found to be much faster than those performed in solutions of either homopolymer (HP). Three MCPs, Cr(CO)6, Fe(CO)5 and Co2(CO)8, were used to show that this phenomenon is not specific to the type of MCP, but rather, to the type of polymer in solution. Furthermore, arrangement of the BCP in solution into core-shell domains created self-assembled "nanoreactors" with PS acting as the surrounding shell while the core PMMA domain contained a high precursor concentration, resulting in faster kinetics. The arrangement of the BCP into these ordered structures in solution does not occur spontaneously, but is rather facilitated by a synergistic coupling effect with the MCP. Finally Cr2O3 NPs synthesized in a BCP solution were shown to form thin complex periodic films that exhibit the preferential incorporation of the NPs into one BCP domain (specifically PMMA). It is also very important to note that although the addition of NPs to the BCP matrix essentially causes physical crosslinking between the BCP chains, it does not hinder the ability of the BCP to self-assemble into its thermodynamically driven dimensional structure.