Polymer Nanocomposites via Surface Functionalization of Nanoparticles: Synthesis, Characterization, and Applications

Abstract

Nanoparticles have been extensively studied because they possess novel properties that come from the quantum effect and a high surface area to volume ratio. Among the many interesting applications of nanoparticles, polymer nanocomposites have been studied extensively because nano-sized inorganic materials are expected to effectively enhance the thermal, mechanical, and electrical properties of polymers without sacrificing the advantages of polymers such as flexibility and easy processability. In this thesis, various polymer nanocomposites were fabricated by incorporating nanoparticles via surface functionalization with a ligand that has a structure similar to polymer repeating unit in order to enhance compatibility between polymer and nanoparticle. As a result, nanoparticles were successfully incorporated in polymer matrices without aggregation. Various metal oxide such as SiO2, TiO2 and BaTiO3 were used as nanofiller due to their high thermal stability, mechanical properties, and outstanding electrical properties (high-k). Thermal, mechanical, and electrical properties of polymer nanocomposites were investigated depending on the content of nanoparticles. Also polymer nanocomposite with enhanced electrical properties was applied to an organic thin film transistor. The thesis chapters are organized by the following. Chapter 1 briefly describes the research background of polymer nanocomposites, categorization of synthetic methods of polymer nanocomposites, surface modification of nanoparticles, and the application of polymer nanocomposites. In Chapter 2, SiO2-Triacethylcellulose (TAC) nanocomposite films having up to 40 wt% of incorporated silica nanoparticles were successfully fabricated by deliberately designing a surface ligand that has a structure similar to that of TAC repeating units and effectively modifying the surface of silica nanoparticles through chemical bonding. The thermal properties including glass transition temperature (Tg), crystallization temperature (Tc), and melting temperatures (Tm) and optical properties of SiO2-TAC nanocomposite were investigated. In Chapter 3, SiO2-polyimide (PI) nanocomposites were prepared by surface modification of silica nanoparticles in order to create structural similarity between the polyimide and the SiO2 surface. SiO2-PI nanocomposites showed enhanced processability (low glass transition temperature), thermal (coefficient of thermal expansion) and mechanical (hardness and modulus) properties. In Chapter 4, TiO2-polyvinylphenol (PVP) and BaTiO3-PVP nanocomposites were successfully fabricated by ligand exchange with 4-hydroxybenzoic acid, which is similar in structure to the repeat unit in PVP. The dielectric constant of PVP nanocomposites was increased by high-k TiO2 and BaTiO3. As a result, organic thin film transistors (OTFTs) with TiO2-PVP nanocomposites dielectric exhibited enhanced device performance.