Dispersion States and Surface Characteristics of Physically Blended Polyhedral Oligomeric Silsesquioxane/Polymer Hybrid Nanocomposites
Control of dispersion and segregation states of nanostructured additives is one of the biggest challenges in realizing the optimum potential of high performance hybrid polymer nanocomposites. Polyhedral oligomeric silsesquioxane (POSS) nanostructured chemicals, with their hybrid organic-inorganic nature and flexible functionalization with a variety of organic substituents, yield possibilities to control dispersion and tune compatibility in a wide range of polymer systems. The overall goal of this research is to investigate the fundamental parameters that influence the dispersion and segregation states of POSS nanostructured chemicals, and to understand chain dynamics and conformations in physically blended POSS hybrid polymer nanocomposites (HPNC's). Multiple structural and mechanical factors influencing macro to nano scale surface and bulk properties were successfully investigated and correlated. A strategy based on thermodynamic principles for selective control of POSS dispersion states in a given polymer matrix is developed and discussed. This dissertation consists of eight chapters. Chapter 1 provides a detailed introduction about the development and current research interest in POSS/polymer nanocomposites. This chapter also discusses limitations of current advanced nanoprobe techniques. Chapter 2 establishes the overall goal of this research and specific research ii objectives. Chapter 3 establishes the preferential surface migration behavior of physically dispersed, non-reactive, closed cage octaisobutyl POSS (Oib-POSS) in a non-polar polypropylene matrix. Furthermore, influence of POSS surface segregation on the surface properties, especially nano-tribomechanical behavior is also discussed. Chapter 4 expands the studies by melt blending two different types of POSS molecules, a non-reactive, closed cage Oib-POSS and an open cage trisilanolphenyl POSS (Tsp-POSS), in a nylon 6 matrix. This chapter discusses the morphology, nano-dispersion and macro- to nanoscale tribomechanical characteristics in relation to the POSS structures. Chapter 5 probes the molecular miscibility, solution and solid-state chain dynamics in polystyrene solution blended with Oib- and Tsp-POSS based on classical thermodynamic principles. Chapter 6 extends the learnings from chapter 5 to utilize POSS as a dispersion aid to disperse TiO 2 nanoparticles in polypropylene. Chapter 7 explores the surface properties of fluorinated and non-fluorinated POSS coated fabrics. Finally, chapter 8 explores a nature-inspired route to modify polymer surfaces utilizing hydrophobin proteins and their impact on surface morphology and nanotribological characteristics.