| Polymers filled with nanoparticles have recently gained much attention in part due to having properties not predicted by previous work on composites with micron-scale particles. Interfaces between fillers and polymer matrices have a significant impact on composite properties. Nanoparticles have large surface area to volume ratios hence additions of small amounts to polymers introduces a large amount of filler/matrix interface.; One challenge in polymer nanocomposites is an inability to predict their properties. The goal of this thesis was to develop quantitative methods for predicting the glass transition temperature in polymer nanocomposites. Two approaches to modifying matrix/filler interactions were investigated. The first used short molecules, to alter the enthalpic interactions, and the second long grafted polymers, to alter the entropic interactions.; Silica particles with surface-grafted short fluorinated chains and bare particles were dispersed in poly(methyl methacrylate) and polystyrene. The work of spreading per unit volume was calculated. This parameter includes the enthalpic interaction (through surface energies) and the interfacial area (through particle size and loading). It was found that both the increases and decreases in glass transition temperature could be predicted with this simple approach.; Long polystyrene chains were grown from the surfaces of silica nanoparticles to make spherical brushes. Spherical brushes in solution were investigated using dynamic light scattering. They consist of three regions, the particle, an inner shell where the height scales with N and r squared but is independent of sigma, and an outer shell where the height scales with N to the power 0.6 and sigma to the power 0.3. This suggests that the inner region is brush like and that the outer region behaves like a homopolymer in solution.; Interactions between spherical brushes and homopolymers were probed. A wettability map was produced and it was shown that spherical brushes are wettable over a wider range of parameters than flat brushes. The boundary between wetting and non-wetting regions was consistent using both glass transition temperatures and wetting measurements. Small angle neutron scattering on protonated homopolymer brushes in deuterated matrices was shown to be a valid method for measuring brush sizes in matrices. |
