Self-Suspended Nanoparticle Fluids
This work undertakes the fundamental study of structure and dynamics of an entirely new class of organic-inorganic hybrid material created by densely grafting polymer chains to the nanoparticle surface. These systems can display fluid behavior even in the absence of any external solvent and have been termed as self-suspended nanoparticle fluids. This materials platform offers several technical opportunities and presents an entirely new system for fundamental studies. Nanoparticle volume fraction and tethered polymer molecular weight in this system can be changed in a straightforward way, allowing the structure and dynamics to be studied over a wide range. We have studied rheology, nanoparticle structure, tethered polymer dynamics and nanoparticle dynamics in this system to understand the governing interaction forces. Flow behavior has been studied by conventional steady and oscillatory shear rheology, nanoparticle structure has been studied by Small Angle X -ray Scattering (SAXS), tethered polymer dynamics has been studied by Broadband Dielectric Spectroscopy and Nanoparticle dynamics has been studied by X-ray Photon Correlation Spectroscopy (XPCS). We have discovered that these materials display characteristic rheological features of soft glassy materials and can be used as model systems to study soft colloidal glasses. In this work we have discovered several unexplored feature of soft glassy materials like the enhanced jamming with increasing temperature and accelerated dynamics with the application of shear strain. We have described our finding in the framework of soft glassy rheology (SGR) model. Tethered polymers in this system exhibit unexpected slow relaxation dynamics irrespective of their low molecular weight, which resembles the features observed in highly entangled polymers. We have proposed a simple theoretical framework to describe the relaxation dynamics of densely grafted polymers that captures the observed behavior. Nanoparticle dynamics in these materials exhibits slow and hyperdiffusive behavior, which follows the similar trends observed in rheology, indicating that the particle dynamics primarily governs the rheology. We have further extended this platform to create hybrid polymer networks having nanoparticles as junction points. These polymer networks exhibit unprecedented mechanical properties and display shape memory properties.
Polymer Nanocomposites; Slow dynamics; Soft glasses
Archer, Lynden A.
Wiesner, Ulrich B.; Koch, Donald L
Ph.D. of Chemical Engineering
Doctor of Philosophy
dissertation or thesis