Date of Award

5-2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Materials Science and Engineering

Advisor

Luo, Jian

Committee Member

Kornev , Konstantin

Committee Member

Luzinov , Igor

Committee Member

Richardson , Kathleen

Abstract

Two new classes of all-inorganic nanostructured multilayers, {MMTx-(sol-gel oxide)}n and {MMTx-(oxide nanoparticle)}n, have been successfully synthesized for the first time. They were made by adapting a layer-by-layer (LbL) assembly method initially developed to synthesize polyelectrolyte-based multilayers. In most previous studies, this electrostatic-assisted LbL assembly method used polyelectrolytes/polymers as the 'structural glue' to prepare multilayers. The synthesis of {MMTx-(sol-gel ZrO2)}n multilayers demonstrates for the first time the feasibility of making sol-gel oxide 'glued' all-inorganic multilayers, thereby introducing an innovative nanoscale fabrication concept. The synthesis of {MMTx-(oxide nanoparticle)}n multilayers further illustrates the versatility of LbL assembly technique by achieving a second new type of all-inorganic multilayers with a novel 'plate-ball' architecture. The feasibility of synthesizing other types of multilayer structures, including {MMTx-(ionic liquid)}n, {(carbon nanotube)-(sol-gel ZrO2)}n, and {polymer-(sol-gel ZrO2)}n, were also explored.
Systematical investigations of the growth kinetics of {MMTx-(sol-gel ZrO2)}n multilayers reveal unique underlying mechanisms for electrostatic-assisted growth of sol-gel films and LbL assembly. The growth of the MMT and sol-gel ZrO2 layers is strongly coupled. For fresh aqueous ZrO2 precursors, the growth rates of sol-gel ZrO2 layers on MMT surfaces as functions of time and precursor concentration do not follow the standard mass transfer or interfacial reaction controlled kinetic models. Furthermore, the growth of the sol-gel oxide layers on MMT surfaces is self-limited to a maximum thickness of ~50-60 nm. These observations suggest a surface-mediated growth of sol-gel oxide layers on MMT surfaces, one that is likely controlled by electrostatic interactions. These new findings significantly advance the general understanding of the LbL electrostatic assembly process. For the aged precursors, the growth mechanism differs; the growth of sol-gel oxide layers is controlled by hydrodynamics and follows the Landau-Levich model. For as-deposited multilayers, isothermal annealing at ~400 °C dehydrates them and removes the residue acetate groups without damaging the MMT nanoplatelets and the ordered layer structures. Nanomechanical measurements show that the elastic modulus of the multilayers can be intentionally tuned by changing the multilayer design and that significant porosity is present in the multilayers even after annealing. In addition, free-standing multilayers are successfully made via using sacrificial substrates, and the newly developed methodology for {MMTx-(sol-gel oxide)}n can be extended, using other metal oxides, e.g., SnO2, as the inorganic 'glue.' Potential applications of these new nanostructured multilayers are discussed.

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