Ceria Nanoparticle Hybrid Materials : Interfacial Design and Structure Control

Sammanfattning: This doctoral thesis addresses the challenge of bringing two very different materials into intimate chemical contact: inorganic metal oxide nanoparticles and acrylic polymers. In order to achieve this ambitious goal, the work has been divided into a series of more accessible tasks. Pedagogically designed, these tasks build upon one another to finally develop the knowledge and skills necessary to successfully formulate novel nanocomposites.A fundamental study on the bulk and surface bonding of ceria was carried out to show that, due to the ceria content in small and highly charged ions, which are difficult to polarize, the preferred chemical interactions are ionic. Among the different capping agents, the carboxylate ligands —through the rich and localized electron density of their oxygen atoms— formed an ionic bond with cerium oxides. This provided stability to the ceria nanoparticles and opened up a vast robust and versatile library of carboxylates to us. This is exemplified by the development of synthetic routes for understanding and modifying ceria nanoparticles with carboxylic acids carrying reactive moieties, which were used to extend the stability of the nanoparticle dispersions. This allowed us to perform in situ polymerization, which resulted in homogeneous ceria–polymer hybrid nanocomposites. This interfacial design offers not only structure control but also strong bonding between the covalent polymer network and the ionic nanocrystals.The focus of the present work, however, is not on characterization of the polymeric materials used but rather on how the embedded nanoparticles interact with the polymeric matrix with respect to chemical interfacial aspects. The following cases were studied: i) unreactive nanoceria dispersed in a polymer matrix; ii) dispersed nanoceria endowed with the ability to initiate polymerizations; and iii) dispersed nanoceria capable of copolymerizing with the propagating chains of the polymer.These processes led to the development of novel hybrid nanocomposites that preserved the optical properties of ceria (e.g. UV absorption) while enhancing mechanical properties such as stiffness and glass transition temperature.