Molecular dynamics in complex nanocomposites as studied by dielectric relaxation spectroscopy (DRS) and dynamic mechanical spectroscopy (DMS)

The dynamics of POSS/polymer nanocomposites were investigated in this work. POSS with different functional side groups were selected to explore the effect of molecular structure of nanoparticles. PPOs and PPO/PEO copolymers with different molecular weight were employed as polymer matrix. Dynamic behavior is investigated by broadband dielectric relaxation spectroscopy (DRS) and dynamic mechanical spectroscopy (DMS) over a wide range of frequency and temperature. The comparison between DRS and DMS provides fundamental understanding of molecular dynamics and the interplay between nanoparticles and polymer chain.;This thesis research consists of five parts: (1) A study of dynamics of neat POSS nanoparticles, presented in chapter 3. This study is performed by DRS on POSS with different structure of functional side groups. (2) non-reactive POSS/PPO nanocomposites were studied in chapter 4. The effects of structure, concentration and dispersion of POSS, molecular weight of PPO and temperature on dynamics of nanocomposites is provided. (3) A study of the relaxation phenomena in reactive POSS/PPO nanocomposites is discussed in chapter 5, including the effect on molecular dynamics of POSS molecular architecture and molecular weight of PPO. The changes in dynamic are recorded as a function of the advancement of cure. (4) The dynamics of PEGylated nanoparticles is revealed in chapter 6. Two amorphous and two semicrystalline PPO/PEO copolymers were selected to functionalize the POSS molecules. Systematic experiments were performed to understand the effects of copolymer molecular weight, PPO/PEO ratio and crystallinity on the molecular motions. (5) A comprehensive study of proteins in hydrated state and aqueous solutions by DRS is introduced in chapter 6. Protein-water interactions were interpreted by dielectric relaxation processes.