Polymer assisted synthesis of functional nano-materials
Liang, Yen Nan
Date of Issue2013
School of Materials Science and Engineering
Polymer assisted solution synthesis is a common and versatile strategy for preparation of colloidal inorganic nano-materials with novel morphological and functional properties. Although block copolymers are usually employed, homopolymers are attractive substitutes for them, considering cost and scalability. This however requires further understanding and more stringent control of the interaction between homopolymer and precursor species. The objective of this work is to utilize functional homopolymers to control the structural properties and chemical compositions of synthesized nano-materials. This objective is approached through detailed studies on two hybrid material systems useful for energy-related applications: (i) aqueous-based poly(acrylic acid) (PAA) templated synthesis of copper oxide (CuOx); and (ii) organic solvent-based poly(3-hexyl thiophene) (P3HT) assisted synthesis of CuInSe2 (CISe) nano-particles. The chosen homopolymers are good representatives of its own category: PAA has an aliphatic, flexible, and ion conducting backbone; while P3HT is an aromatic, rigid, and semiconducting polymer. The bridging of the theoretical studies of PAA-Cu2+ interaction and PAA templated synthesis is attempted. In the CuOx project, investigation on the PAA-Cu2+ interaction was carried out. Important factors including [Cu2+]:[COOH]0, chain conformation, and non-uniform equilibrium charge distribution were identified to have contributed to counterion induced copolymer-like assembly of the PAA-Cu2+ complexes, eventually producing nano-tubular CuOx. The challenging control of stoichiometry and its uniformity is known to be an issue in tailoring the functional properties of CISe nano-particles. In the CISe project, CISe nano-particles having novel stoichiometric gradient (i.e. increasing In:Cu ratio from core to shell) and coordinated with P3HT were prepared. Synthesis systems without P3HT were carefully studied and a mechanism leading to novel core-shell-like stoichiometry is proposed. With employment of P3HT as functional ligands, the stoichiometric gradient could be moderated. This work investigates fundamental molecular-level phenomena associated with the starting precursor conversion, stabilized intermediate state, and eventual crystal growth. The concept and methodology developed can be extended to relevant material systems. This work highlights the vast opportunities remained to be explored in utilizing functional homopolymers for controlled synthesis of nano-materials. It can contribute to the fields of fundamental polymer science, inorganic nano-materials formation chemistry, as well as technological applications for printed electronics.
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