| The states of nanoparticle dispersions in concentrated polymer solutions are studied with extensive small angle scattering and NMR experiments. Silica nanoparticles are suspended in polymer-solvent mixtures. The effects of polymer induced interactions on the particle microstructure are examined with varying (i) polymer concentration, (ii) solvent type, (iii) temperature, (iv) particle volume fraction and (v) polymer chemistry while polymer-to-solvent volume ratio is held between 0.45 and 1. The local order and long wave length concentration fluctuations of nanoparticles are obtained from the analysis of scattering structure factors and compared with the Polymer Reference Site Interaction Model (PRISM) theory. Exploiting contrast matching small-angle neutron scattering all partial collective structure factors of particles, polymers and their interface are characterized establishing the existence and size o f adsorbed polymer layers. Comparisons of experimental structure factors to PRISM predictions yield a key parameter, the polymer segment-nanoparticle attractive contact interaction energy. This cohesive energy controls the state of particle and polymer dispersions. The thermodynamic information obtained in these experiments is linked to the polymer dynamics using free induction decay of NMR experiments, which directly quantify the amount of polymer adsorption while multi-quantum NMR experiments probe the existence of physical crosslinks and entanglements. Taken together this thesis provides detailed information of nanoparticle dispersions in dense polymer solutions and polymer nanocomposites and insight into how to manipulate particles and polymer to control particle aggregation. |
