Microscopic View on Structure and Dynamics in Polymer Nanocomposites

Abstract

The focus of this thesis is on the single chain conformation and dynamics in polymer melts, nanocomposite melts and networks. The exploration of structure, morphology and dynamics has shown to be crucial to understand the basic science in such systems, like the influence of entropy, confinement, and monomeric friction. These parameters can be translated into the macroscopic behavior of the materials. The scientific work on model nanocomposite systems contributes to accelerate the development of materials, and also to invent to date unknown materials with uprecedented properties, needed for car tires, low weight but ultra strong materials or batteries. This thesis concentrates on the large-scale structure and dynamics, including the conformation of polymer chains and the parameters associated with the size and spatial distribution of nanoparticles in the polymeric matrices. The core tools are Small-Angle X-ray Scattering (SAXS) and Small-Angle Neutron Scattering (SANS) to record the structure and conformation, respectively. Neutron Spin Echo (NSE) spectroscopy is used to follow the entropy driven chain dynamics. Previous work has shown that NSE in concert with SAXS and SANS can lead to an unparalled insight into the (macro-) molecular parameters. This work presents structural studies on polymer particle interactions, polymer particle interphase formation processes and an anaysis of morphological changes in systems containing polymer and nanoparticles by using the SANS zero average contrast method in solution. The structure and chain conformation of interphase polymer formed by polymer particle interaction is compared to the chain conformation of polymer grafted on silica nanoparticles which were considered as model polymer particle interphases. Furthermore a detailed analysis of studies on structure and large scale chain dynamics in silica filled model nanocomposites are presented. The studies uses polymers with a molecular weight in between the transition region from unentangled to entangled polmer melts. The presented studies revealed, that chosing polydimethylsiloxane as polymer with a molecular weight in this transition region allows to get the full picture of the chain dynamics, including the contributions associated with the finite size of the polymer chains.