Synthesis, Assembly and Colloidal Polymerization of Polymer-Coated Ferromagnetic Cobalt Nanoparticles

Abstract

This dissertation describes a novel methodology to prepare, functionalize, and assemble polymer-coated ferromagnetic cobalt nanoparticles (PS-CoNPs) and cobalt oxide nanowires. This research demonstrated the ability to use dipolar nanoparticles as `colloidal monomers' to form electroactive 1-D mesostructures via self- and field-induced assembly. The central focus of this dissertation is in developing a novel methodology termed as `Colloidal Polymerization', in the synthesis of well-defined cobalt oxide nanowires as nanostructured electrode materials for potential applications in energy storage and conversion.Ferromagnetic nanoparticles are versatile building blocks due to their inherent spin dipole, which drive 1-D self-assembly of colloids. However, the preparation and utilization of ferromagnetic nanoparticles have not been extensively examined due to the synthetic challenges in preparing well-defined materials that can be easily handled. This dissertation has overcome these challenges through the hybridization of polymeric surfactants with an inorganic colloid to impart functionality, colloidal stability and improved processing characteristics. This modular synthetic approach was further simplified to prepare ferromagnetic nanoparticles in gram scale, which enabled further investigations to develop new chemistry and materials science with these materials. These polymer-coated magnetic nanoparticles self-assembled into extended linear chains due to strong dipolar attractions between colloids. Additionally, novel dipolar assemblies, such as, flux-closure nanorings and lamellae type mesostructures were demonstrated by controlling the interparticle of attractive forces (dipolar versus van der Waals).The research presented herein focused on utilizing polymer-coated ferromagnetic cobalt nanoparticles as `colloidal molecules' to form interconnected 1-D mesostructures via `Colloidal Polymerization'. This process exploited the magnetic organization of dipolar colloids into 1-D mesostructures followed by a facile oxidation reaction to form interconnected electroactive cobalt oxide nanowires. This facile and template free approach enabled the large scale synthesis of semiconductor cobalt oxide nanowires, in which the electronic and electrochemical properties were confirmed for potential applications for energy storage and conversion. This work served as a platform in fabricating a wide range of semiconductor heterostructures, which allowed for structure-property investigation of new nanostructured electrodes.